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Silicosis in Metal Mining

SILICOSIS IN THE METAL MINING INDUSTRY A Revaluation • 1958-1961 U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE PUBLIC HEALTH SERVICE o° 1 Robert H. Flinn, M.D.; Hugh P. Brinton, Ph. D.; Henry N. Doyle, - •q Lewis J. Cralley, Ph. D.; Robert L. Harris, Jr. '9 1 U.S. DEPARTMENT OF THE INTERIOR 9 0 m I BUREAU OF MINES ~ ~ Yames Wesoeld; ,J. Howard Bird; Lawrence B. Berger

Study Coordinator, Bureau of Mines : James Westfield Study Coordinator, Public Health Service : Henry N. Doyle Director of Medical Studies : Robert H. Flinn, M.D. Director of Environmental Studies : J. Howard Bird INTERAGENCY TECHNICAL COMMITTEE Public Health Service Bureau of Mines LEWIs J. CRALLEY, PH. D. LAWRENCE B. BERGER W. CLARS COOPER, M.D. J. HOWARD BIRD HENRY N. DOYLE JoHN A. JOHNSON ROSERT H. FISxN, M.D. JAMES WESmFIELD RosERT L. HARRIS, JR., Secretary PANEL OF ROENTGENOLOGISTS BENJAMIN FEL6oN, M.D., University of Cincinnati, College of Medicine GEORGE JACOBsON, M.D., University of Southern California, School of Medicine EUGENE P. PENDERGRASS, M.D., Hospital of the University of Pennsylvania Public Health Service Publication No. 1076 U.$. GOVERNMENT PRINTING OFFICE WASHINGTON t 1963 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C., 20402 - Price $1.25 (Paper Cover) Foreword Throughout the history of mining, silicosis has been a major health problem. Efforts to control the disease did not begin in the United States until shortly after the turn of the 20th century, when the Pub- lic Health Service and the Bureau of Mines embarked on a series of joint investigations which contributed much basic knowledge on the etiology, pathology, and control of silicosis. However, it was not until about 1935 that the mining industries began major efforts to control the disease. Because of the long period involved in the devel- opment of silicosis, these efforts were not expected to lead to a de- monstrable reduction in the prevalence of silicosis until many years later. In 1956, a study of compensation and other records pointed up the disease as a continuing problem of industrial, social, and eco- nomic significance. The present study was an outgrowth of hear- ings on mine health and safety held by the Committee on Education and Labor, House of Representatives, 84th Congress. Because of the inadequacy of retrospective data on dust concen- trations in the mines and silicosis prevalence rates due to the dearth of mine studies during the period 1940-61, it was not possible to an- swer all of the questions proposed in the objectives of the study. The study, however, should form the basis for others which could mate- rially assist in ultimately eliminating silicosis as a serious threat to the health of metal miners. qa4v a-~ 011n^m MARLING J. ANKENY HARRY HEIMANN, M.D. Director, Bureau of Mines Chie f, Division of Occupational Department of the Interior Health Bureau of State Services Public Health Service Department of Health, Educa- tion, and Welfare V

Acknowledgments I Appreciation is expressed to the participating mining companies and labor unions for their excellent cooperation. Likewise, valuable assistance in organizing the study was given by the American Mining Congress and the various State mining associations. Without the assistance and cooperation of the State health departments and the State mining agencies it would have been impossible to carry out the study. In addition, the success of a comprehensive study of this type depends upon the specialized skills of many individuals. The au- thors wish especially to acknowledge the following contributions in the environmental and medical aspects of the study. Bureau o f[llines-Members of the Health and Safety Activity of the Bureau of Mines performed as an effective team in both field and laboratory activities. Field studies were accomplished as sched- uled, and laboratory production of analytical results kept pace with field operations. Particular acknowledgment is made of the contributions to this report by Floyd G. Anderson, who participated in preparation of the section on History of Dust Sampling and Comparison of Methods; by Arthur L. Franks, Jr., Leslie Johnson, and Paul Schapiro, who analyzed field data and prepared material for the report; and by Joseph B. Stepan, who prepared the section entitled "Review of Environmental and Historical Records." Leslie Johnson was in charge of field operations, and Arthur L. Franks, Jr., and Paul P. Schapiro served as team leaders. Others who took part in the field studies at various times were E. F. Allen, Walter Bank, R. C. Bates, C. J. Beecroft, R. L. Ber- nard, J. L. Brandt, W. B. Brogoitti, R. Capps, R. C. Derzay, A. M. Evans, R. L. Evans, G. B. Fritts, J. A. Fulmer, J. P. Harmon, T. Jolley, R. G. Peluso, H. G. Plimpton, E. J. Podgorski, H. E. Poland, R. O. Pynnonen, R. L. Rock, K. U. Russell, H. L. Schell, A. Schrader, D. K. Walker, M. L. Williams, and G. D. Winans. Laboratory operations were conducted at Bureau of Mines stations at Pittsburgh, Pa., and Denver, Colo. At Pittsburgh, Floyd G. Ander- son supervised particle-size determinations by optical microscopy, and i I t vn

Peter J. Colbassani supervised X-ray diffraction and spectrographic determinations. At Denver, Russell Faddis and Harrison Hudson participated in operations pertaining to assessment of airborne dust, and Albert Maxian supervised analyses of all samples of mine air collected during the study. Public Health Service=Staff members of the Division of Occupa- tional Health located both at the Occupational Health Research and Training Facility at Cincinnati, Ohio, and at the Occupational Health Field Station, Salt Lake City, Utah, participated in the medical studies. Special appreciation is due to the following medical officers who conducted the examinations of miners: Mike Hayes, M.D.; Thomas H. Milby, M.D.; George H. Franck, M.D.; Raymond T. Moore, M.D.; Rodger K. Farr, M.D.; Robert Collier, M.D.; Nicholas P. Sinaly, M.D.; Patrick J. Hennelly, M.D.; Neely E. Pardee, M.D.; Willard P. Johnson, M.D.; and L. Bruce Bachman, M.D.; in addi- tion, Victor E. Archer, M.D., conducted the medical examinations reported herein from the Uranium Miners' Survey of 1960. Likewise, appreciation is extended to Roy J. Hanna and Rickard D. Hutchison, who participated in the special engineering studies; to Darrell E. Anderson who participated` in both the medical and environmental studies; to Robert G. Keenan, Frances Hyslop, and David A. Fraser, Ph. D., for special analytical work on selected field samples; and to Louis Pecora, Ph. D., for his work on physiology. Mr. Nicholas E. Manos is responsible for the development of the methodology and analyses of the field data obtained from the tests of pulmonary ventilatory function described in Appendix A. Much credit goes to Duncan Holaday for his assistance in get- ting the field work underway; to James Mueller and Frances E. Brogan for their help in the administrative phases of the study; and to Norma L. Egnew, Pius Zimmer, Helen McCool, and Mary Gabriel for their assistance with the statistical analyses. Miss Victoria Trasko has rendered valuable service in the final editing and collating of the manuscript. The material presented as a retrospective study of a major sili- cosis control program was made possible by the enthusiastic coop- eration extended by Dr. George W. Wright and Mr. Robert Downs of the Saranac Laboratory, and officials of the cooperating mining companies in the Lake Superior district, especially those of the Oglebay Norton Mining Co. and its Montreal mine, located at Mon- treal, Wis. vIn Contents Page FOREWORD- - --- --------------- -- --- ------- -- V .. CKNOWLEDOMENTS------------------- ------------------- Vn CHAPTER I INTRODUCTION-------------------------------------------- Background----------------------------------------- Methodology---------------------------------------- References------------------------------------------ CHAPTER II 1 1 4 8 SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS------------ 11 Summary------------------------------------------- 11 EnvironmentalStudy---------------------------- 12 Medical Study---------------------------------- 15 C.onclusions----------------------------------------- 19 Recommendations------------------------------------ 21 General---------------------------------------- 21 The Working Environment----------------------- 22 Medical Services-------------------------------- 23 CHAPTER III REVIEW OF PAST STUDIES-------------------------------- 27 References----------- I ------------------------------ 30 CHAPTER IV THE ENVIRONMENTAL STUDY-------------------,.--------- 33 Part A-Field Investigation-------------------------- 33 Purpose and Scope----------------------------------- 33 Geography and Geology of Ore Deposits------------------ 35 Mining Methods------------------------------------- 36 Survey Methods------------------------------------- 36 Field Procedures-------------------------------- 39 Threshold Limit Values-------------------------- 42 ix

THE ENVTRONMENTAL STUDY-Continued Page CHAPTER V Results of Environmental Study------------------------ Particle Size------------------------------------ 45 45 ~ I MEDICAL STUDY----------------------------------------- Page 99 Free Silica Content of Dust---------------------- 47 General Procedures----------------------------------- 99 Dust Concentrations------------------------------ 48 Personnel and Facilities----.---------------------- 99 Mines Studied 100 Underground-General-------------------------- 53 ---------------------------------- Underground Operations------------------------- 53 , Examination Procedures------------------------- 100 The Population Sample Examined------ 101 Man Trips--------------------------------- 56 ----------- Procedure of Medical Examinations--------------------- 104 Slushing------------------------------------ 56 Medical History and Symptoms- ----------------- 104 Mucking----------------------------------- 56 Occupational History---------------------------- 105 Timbering---------------------------------- 56 Chest Roentgenograms--------------------------- 106 Drilling and Loading Holes------------------- 56 Pulmonary Ventilatory Function 7.'ests 107 Tramming ----------- - - ----- - - 58 I ------------ - Forced Expirogram -- 107 - - - - - -------- - Loading and Dumping Cars------------------ 58 I i ---- -----------.--------- Maximum Forced Expiratory Flow Rate------- 107 Skip Tenders------------------------------- Between Operations------------------------- 58 58 i i Conditions of Testing------------------------ Characteristics of Workers Examined------------------- 108 108 Age and Occupation 108 Eating Lunch------------------------------- 58 ~ ----------------------------- Years in Principal Occupation 112 Concrete and Gunite Crews------------------- 59 -------------------- Rock Bolting 59 r Years in Present Occupation -------------------- 112 ------------------------------- Analysis of Medical Findings-------------------------- 117 Mobile Equipment Operators----------------- 59 Analysis of Chest Roentgenograms---------------- 117 Barring Down------------------------------ 59 General Procedure--------------------------- 117 Breaking Boulders--------------------------- 59 Classification of Roentgenograms-------------- 117 Mills and Crushers------------------------------ 60 Roentgenograms Classified as Silicotic--------- 118 Mills-------------------------------------- 60 History of Past Illnesses------------------------- 126 Crushers----------------------------------- 60 ChestIllnesses------------------------------ 126 Assayers in Mills.--------------------------- 62 r Tuberculosis-------------------------------- 127 Shops and Other Surface Locations---------------- 62 Heart Trouble------------------------------ 132 Shops-------------------------------------- 64 Rheumatic Fever---------------------------- 132 Assay Laboratories-------------------------- 64 Rheumatism-------------------------------- 132 Dust on Lungs 133 Concentrate Loaders------------------------- 64 ------------------------------ History of Lead Poisoning 133 Concrete Plants----------------------------- 64 -------------------- History of Mercurial Poisoning - 134 Other Operations---------------------------- 64 --- ------------ Frequency of Present Symptoms------------------ 134 Dust Control----------------------------------- 70 ChestIllness-------------------------------- 134 VentiIation------------------------------------- 71 ~ Shortness of Breath-------------------------- 135 Composition of Mine Atmospheres-----,.---------- Conclusions on Dust Production and Control------- 72 76 Silicosis Related to Type and Duration of Exposure-- Years in Metal Mining----------------------- 140 140 i References------------------------------------------ 76 Age of Workers----------------------------- 141 Part B-History of Dust Sampling and Comparison of Methods----------------------------------------- References------------------------------------------ 77 94 Age and Years in Metal Mining--------------- Years in Metal Mining and Principal Occupa- tion------------------------------------- 144 144 I: Present Occupation-------------------------- 152 Present Occupation Compared With Principal Occupation------------------------------- 152 x xi

MEDICAL STUDY-COntmued APPENDIX Analysis of Medical Findings-Continued, Silicosis Related to Type and Duration of Exposure- Continued Geographical Location_______________________ Page 156 EFFECTS OF SILICOSIS AND OTHER FACTORS ON PULMONARY F_UNCTION---- ---------------------------------------- Page 231 Silicosis According to Commodity Produced_ ___ 156 Introduction---------------------------------------- 231 Workers With Experience at One Mine Only Effects of Silicosis on Pulmonary Function_____________ 232 and at Two or More Mines_________________ 159 Effects of Other Factor~ on Pulmonary Function-------- 236 Silicosis Among Workers Excluded Because of ~ Correlation Between Four Measurements of Pulmonary Other Dusty Work________________________ 162 Function------------------------------------------ 237 Silicosis by Periods of Work Experience Before ~ - and After 1935____________________________ Comparison of Present With Past Studies---------------- 162 164 TABLES Case Histories--------------------------------------- 169 Table IV.1.-Data on mines included in the dust study------ 33 Health Services-------------------------------------- 180 Table IV.2.-Host rock and alpha quartz correlation---_--_- 35 References------------------------------------------ 181 Table IV.3.-Distribution of 67 mines according to principal mining method ------------ - -- 36 CHAPTER VI A RETROSPECTIVE STUDY OF A SILICOSIS CONTROL PROORAM__ 185 ------------------------ - -- Table IV.4.-Number of midget impinger samples collected for determination of airborne dust concentrations____-_--_- 41 Background----------------------------------------- 185 Table IV.5.-Samples collected during the study------------ 41 The Study of Medical Records From One Mine _ _ _ _ _ _ _ _ _ _ _ Description of the Members of the Study Group____ 188 190 Table IV.6.-Comparison of 55 particle-size analyses by elec- tron and optical microscopy____________________________ 45 Workers With Silicosis___________________________ Work History, Subsequent to 1933, of Employees 192 Table IV.7.-Particle-size characteristics of 481 samples exam- ined by optical microscopy_____________________________ 46 With Silicosis--------------------------------- 194 Table IV.8.-Free silica content of settled dust at 67 mines_-_ 48 Presilicotic Changes_____________________________ The Review of Environmental and Historical Records------ 196 199 Table IV.9.-Distribution of weighted average exposures that exceeded threshold limit values-------------------------- 51 History of Operations and General Information___-_ 199 I Table IV.10. Occupational dust exposures, underground, Geology----------------------------------------- 200 weighted averages-------- .----------------------------- 56 Total and Free Silica Determination----------- 202 ~ Table IV.11.-Midget impinger samples collected at surface Mining Methods________________________________ 202 and underground mills and crushers_____________________ 60 History of Organized Safety Activity-------------- Ventilation------------------------------------- 204 206 Table IV.12.-Midget impinger samples collected at Surface locations---------------------------------------------- 62 Other Ventilation Improvements--------------- History of Dust Control__________________________ 210 210 Table IV.13.-Occupational dust exposures, surface and under- ground, ,.,rithmetic avelages____________________________ 65 Wet Drilling-------------------------------- 210 Table IV.14.-Dust concentrations in underground operations_ 66 Other Use of Water To Control Dust---------- Other Improvements or Dust Control Measures-_ 211 211 Table IV.15.-Occupational dust exposures, surface and under- ground-------- --------------------------------------- 67 Company Dust Counts___________________________ 213 Table IV.16.-Measures to reduce dust exposures----------- 70 Table IV.17.--Practices that caused dusty conditions-------- 71 CHAPTER VII Table IV.18.-Ventilation rates at 53 mines with mechanical ventilation------------------------------------------- 72 THE USE OF THE NEW INTERNATIONAL RADIOLO(31CAL CLAS- SIFICATION OF THE PNEUMOCONIOSES (GENEVA-1958) IN place.s------------------------------------------------- Table IV.19.-Methods of ventilation in underground working 72 THE STUDY OF SILICOSIS________________________________ 219 Table IV.20.-Composition of mine atmospheres------------ 74 References------------------------------------------ 230 Table IV.21.-Methods for determination of dust in air------ 79 xii i I ;F

Table IV.22.-Comparison of dust concentrations from midget impinger samples with concentrations from companion Page samples by other methods------------------------------ 89 Table IV.23.-Settled dust samples------------------------ 92 Table IV.24.-Comparison of free silica content of screened and air elutriated fractions of settled dust with that of com- panion electrostatic precipitator samples of airborne dust_- 93 Table V.1.-Workers at 36 metal mines eligible for a medical examination and those examined according to age and place where working---------------------------------------- Table V.2.-Principal occupation of workers at 50 metal mines 102 according to age--------------------------------------- 110 Table V.3.-Present occupation of workers at 50 metal mines according to age--------------------------------------- 111 Table V.4.-Principal occupations of workers at 50 metal mines according to years worked at metal mines---------------- 114 Table V.S.-Present occupation of workers at 50 metal mines according to years in present occupation----------------- 116 Table V.6.-Distribution of 50 metal mines according to prevalence of silicosis__________________________________ 122 Table V.7.-Percent of metal mine workers with X-ray evidence of silicosis according to size of mine and number of years worked at 50 metal mines and uranium mines------- 123 Table V.8.-Frequency distribution of metal mines by size showing percent of workers with silicosis----------------- 126 Table V.9.-Percent of workers at 50 metal mines with certain present symptoms and past illnesses for silicotic and non- silicotic workers by age and years worked at metal mines--_ 128 Table V.10.-Shortness of breath among workers at 50 metal mines according to lung field markings and years at metal mines------------------------------------------------ 137 Table V.11.-Shortness of breath among workers at 50 metal mines according to detailed lung field markings, age and years at metal mines_- -------------------------------- 139 Table V.12.-Shortness of breath among workers at 50 metal mines according to elevation of mine and age, workers with or without silicosis------------------------------------- 140 Table V.13.-Number and percent of metal mine workers with X-ray evidence of silicosis according to years at metal mines-- 142 Table V.14.-Number and percent of metal mine workers with X-ray evidence of silicosis according to age--------------- 142 Table V.15.-Number and percent of metal mine workers with X-ray evidence of silicosis according to age and years at metal mines------------------------------------------ 145 i t Table V.16.-Percent of workers with 'evidence of silicosis at 50 metal mines according to principal occupation and years Page at metal mines---------------------------------------- 147 Table V.17.-Silicosis among metal mine workers by principal occupation and years at metal mines__ __________________ 150 Table V.18.-Workers at 50 metal mines according to occupa- tion at time of medical examination_____------------------- _ 153 Table V.19.-Present occupation compared with principal occupation of workers at 50 metal mines according to percent with silicosis-------------------------------------------- 154 Table V.20.-Silicosis among metal mine workers according to commodity produced, by years at metal mines----------- 157 Table V.21.-Silicosis among metal mine workers with ex- perience of 10 years or more at one mine only and at two or more mines by principal occupation and years at metal mines- 160 Table V.22.-Silicosis among metal mine workers with exposure in other dusty trades of 5 years or over according to total years in all dusty work________________________________ 162 Table V.23.-Silicosis among workers at metal mines by period of work experience and total years worked at metal mines_ ___ 164 Table V.24:-Silicosis in western lead-zinc mine workers ex- mined in 1958-61 compared with Utah metal mine workers examined in 1939 according to years at metal mines--------- 167 Table V.25.-Weighted average dust concentrations (mppcf) at comparable occupations in 12 lead-zinc mines studied in 1958-61 compared with Utah metal mines studied in 1939____ 167 Table V.26.-Number of 50 metal mines having specified health services according to size of mine------------------- 180 Table VI.1.-X-ray film classification (Saranac) of employees working in iron mines with contracts with the Saranac Laboratory by period examined------------------------- 186 Table VI.2.-Distribution of workers in the study group ac- cording to number at work Jan. 1, 1933, and number who began working in subsequent periods by number of years on company payroll----------------------------------- 191 Table VI.3.-Metal mine workers with silicosis according to age and years in mining when employment with the company wasterminated---------------------------------------- -- 193 Table VI.4.-Mining experience previous to 1933 of workers who had silicosis in 1933 by years worked in one mine only andin twoormoremines------------------------------- 194 Table VI.5.-Mining experience after 1933 of workers who had silicosis in 1933 which did not progress, according to job status and years worked------------------------------- 195 I i i i xiv xv

Table VI.6.-X-ray film readings by the Saranac Laboratory poe of workers with experience before and since 1933 by years in metal mines________________________________________ 197 Table V1.7.-Presilicotic changes in X-ray interpretation of men with 10 years or more of employment who began work in 1933-42, and 1943-52-Montreal mine------------------ 198 Table VL8.-Statistical data on company operations in Mon- treal mine-------------------------------------------- Table VI.9.-Average company dust counts for operations in 201 orein Montreal mine---------------------------------- 214_ Table VI.10.-Average company dust counts for operations in rock in Montreal mine_________________________________ 215 Table VIL1.-I.L.O. radiological classification of silicotic chest films in study group of 14,076 metal mine workers--------- 227 Table VII.2.-I.L.O. categorization of lung field markings by years of work at 50 metal mines_________________________ 228 Table VII.3.-I.L.O. detailed classification of all 14,858 chest roentgenograms taken in metal mines study including 671 employees with exposure in other dusty trades------------ 229 Fiourm Figure I.1.-States in which mine studies were made-------- 7 Figure IV.1.-Acceptable counts for two cells from the same sample----------------------------------------------- 39 Figure IV.2.-Frequency distribption of geometric mean par- ticle sizes--------------------------------------------- 47 Figure IV.3.-Percentage distribution of midget impinger samples by range of free silica content___________________ 49 Figure IV.4. Distribution of weighted average exposure under- ground in respect to threshold limit values---------------- 50 Figure IV.5.-Average of midget impinger samples collected in each mine in respect to dust concentration and free silica content---------------------------------------------- 54 Figure IV.6.-Distribution of midget impinger samples col- lected in respect to dust concentration and free silica con- tent -------------------------------------------------- 55 Figure IV.7.-Ranges and percentages of dust concentrations underground------------------------------------------ 57 Figure IV.8.-Distribution of midget impinger samples col- lected in mill and crusher locations in respect to dust con- centration and free silica content________________________ 61 Figure IV.9.-Distribution of midget impinger samples col- lected in shops and surface locations in respect to dust con- . centration and free silica content________________________ 63 t i i I i r Page Figure V.1.-Medical examination form___------------------ 104 Figure V.2.-Occupational history form____________________ 106 Figure V.3.-International radiological classification of chest films modified for Public Health Service metal mines survey__ 119 Figure V.4.-Definition of terms used in Public. Health__Service modification of I.L.O. radiological classification of chest films for metal minessurvey---------------------------------- 120 Figure V.5.-Frequency distribution of 50 metal mines showing number of cases of simple and complicated silicosis-------- 125 Figure V.6.-Shortness of breath among workers with and without silicosis according to years worked in 50 metal . mines------------------------------------------------ Figure V.7.-Percent of all metal mine workers with silicosis 138 by age----------------------------------------------- 143 Figure V.8.-Percent of metal mine workers. with silicosis according to age and years worked in metal mines--------- 146 Figure V.9.-Percent of metal mine workers with silicosis according to principal occupation and years worked in metal mines--------------------------- --------------------- Figure V. 10..Percent of metal mine workers with silicosis 149 according to commodity produced----------------------- 158 Figure V:11.Dilicosis among metal mine workers with ex- posure of 10 years or more in one mine only, and in two or more mines------------------------------------------- Figure V.12.-Percent of metal mine. workers with silicosis according to period of experience and years worked in metal 161 mines------------------------------------------------ 165 Figure V.13.-Simple silicosis_____________________________ 170 Figure V.14.-Simple silicosis---------------------- -------- 171 Figure V.15.-Siznple silicosis_____________________________ 172 Figure V.16.-Simple silicosis_____________________________ 173 Figure V.17.-Simple silicosis----------------------------- 174 Figure V.18.-Complicated silicosis________________________ 175 Figure V.19.-Complicated silicosis------------------------ 176 Figure V.20.-Complicated silicosis. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ 177 Figure V.21.-Complicated silicosis------------------------ 178 Figure V.22.-Complicated silicosis________________________ 179 Figure VI.1.-Orders to Captains and Bosses-Use of Respira- tors Underground (prepared in 1935 for Montreal mine)__-_ 212 Figure VI.2.-The Montreal Mining Co. Rules for Dust Pre- vention (prepared in 1936)----------------------------- 213 Figure VII.1.-Radiological classification of chest films for Public Health Service metal mines survey_ _ _ _ ___ _ _ 222

PHOTOGRAPHS Page Frontispiece. View of Homestake Mining Co., Lead, S. Dak_ ii Richest Hill on Earth. Butte, Mont. Plumes are from surface fans------------------------------------------ 9 Bishop Mine-Union Carbide Nuclear Co., Bishop, Calif----_ 25 Two-stage 500-horsepower main surface fan-direct expulsion tyPe------------------------------------------------- 32 Sprinkler tank car for wetting haulageways. Rear view------ 37 i Miner operating electric tugger in slushing operation--------- 44 Miner wetting down muck pile and faces prior to mucking op- eration. Note overhead vent tubing and method of ground support----------------------------------------------- I 52 Compressed air and water mist spray used during blasting cycle in headings-------------------------------------- 73 Airlock door and fan on main adit------------------------- 75 Underground dust collector------------------------------- 78 The medical survey unit---------------------------------- 97 Physician interviewing a miner----------------------------- 103 A miner performing a pulmonary function test-------------- 109 The occupational history interview------------------------- 113 Taking the chest X-ray film------------------------------- 141 Smooth lining in airway to reduce frictional resistance and permit increased airflow--------------------------------- 184 Air shaft discharge stack with acoustical lining to reduce noise------------------------------------------------- 217 i xviu CHAPTER I Introduction IN 1956, THE Committee on Education and Labor, House of Rep- resentatives, held a series of hearings on bills introduced in the 84th Congress relating to inspections and investigations in metallic and nonmetallic mines and quarries for the purpose of obtaining infor- mation relating to health, safety conditions, accidents, and occupa- tional diseases therein. Testimony relating to the silicosis problem in the metal mining industry was presented at the December 1956 hearings by representatives of the Public Health Service and the Bureau of Mines. Although the committee did not recommend favorable action on the bills, as an outgrowth of the hearings, the Congress appropriated funds to the Public Health Service and the Bureau of Mines to revaluate the silicosis problem in the metal • --- = mmes. This report presents the major findings of the environmental and clinical studies conducted by the two agencies between March 1958 and September 1961 on the nature and scope of the silicosis problem in the metal mining industry. Also included is a retrospective study of a long-term silicosis control program and a discussion of the use of the International Radiological Classification of the Pneumoconioses in the study of silicosis. _ $ACKGRO.UND The classic studies of the Public Health Service and the Bureau of Mines relating to dust diseases conducted between 1913 and 1940 made several important contribut.ion_ s_ to our knowledge of silicosis. They served to confirm the findings of many independent investiga- tors and assisted in determining the etiology and pathology of the disease. The studies helped immeasurably in the assay of _ dust exposure and in defining the role of such factors as particle size, composition of the dust, and duration of exposure, and led ultimately to the adoption of 5 million particles per cu_bic foot-of air_ as a maxi- I I

ever, that with adequate environmental controls, silicosis might be prevented or its development delayed considerably beyond the 20-year exposure period. A third unexpected opportunity for further study presented itself in December 1956 when the Committee on Education and Labor, House of Representatives, held its major hearing on bills introduced in the 84th Congress relating to inspections and investigations in metallic and nonmetallic mines and quarries.8 A substantial part of the hearing was devoted to the silicosis problem and testimony was presented by the Public Health Service and the Bureau of Mines. As an outgrowth of the hearing, the Congress appropriated funds to the Public Health Service and the Bureau of Mines to revaluate the silicosis problem in the metal mining industry. METHODOLOGY Following the appropriation of funds by the Congress, an Inter- agency Technical Committee composed of three representatives and an alternate each from the Bureau of Mines and the •Public Health Service was appointed in September 1958 to organize and direct a joint study of silicosis in the metal mining industry. A major re- sponsibility of the Committee was to determine objectives, policies, and procedures to be used in the study. The objective of the study was defined as the determination of the prevalence of silicosis and assessment of the present day environmental conditions in the metal mining industry. The study was designed to answer three important questions. These were :(1) Are the cases presently occurring the result of pre-control exposure, in view of the long latent period for the development of silicosis? (2) Are they accounted for by the failure to apply controls universally? (3) Are the silicosis cases occurring because of the inadequacy of standards in use since 1935? The study was limited to active, underground • metal mines em- ploying more than 20 persons underground, but it was broad enough to include all major commodities in the various mining areas of the United States. The medical examinations consisted of a 14- by 17- inch chest roentgenogram, an occupational and medical history, and simple pulmonary function tests of employees of mines included in • the study. Through engineering studies, environmental conditions were eval- uated by determining dust concentrations and existing dust control measures. Dust evaluations included the determination of the con- centration, particle size, and composition of the dust. Airborne dust and dust-source material were analyzed by X-ray diffraction 4 I ) for free silica and by spectrographic methods for chemical com- position. Ventilation rates were measured. Weighted dust expo- sures _ were determined for each major underground occupation. Mine air samples were collected in sufficient numbers to permit the evaluation of exposures to carbon monoxide, carbon dioxide, and oxides of nitrogen. Because previous studies had utilized the impinger and the refer- ence standard was based on this instrument, the Committee agreed that it would be the basic sampling instrument in the environmen- tal study. However, it was felt that it would be well to supplement the impinger with the thermal precipitator, the electrostatic pre- cipitator, and a filter paper sampler. For various technical rea- sons, the thermal precipitator was used for only a portion of the routine study and use of the electrostatic precipitator was limited largely to a special supplemental investigation. The filter paper technique was continued throughout the study, but the sample was only used for particle sizing. For particle-size determination, both j the optical and the electron microscope were used. The Committee, recognizing the importance of exploring various dust quantitation techniques other than the impinger method, agreed that special dust sampling studies would be conducted in laboratories of the Public Health Service and the Bureau of Mines, and in selected mines. These studies were performed to compare the results yielded by a variety of dust sampling and quantitation techniques with those obtained by the standard impinger method as used in the routine surveys. Very early in its deliberations, the Committee concluded that the success of the study would depend upon keeping and presenting the data in such a manner that the identity of the mines and individ- uals would not be disclosed. Such procedures are also in accord- ance with the policies of the Department of the Interior and the De- partment of Health, Education, and Welfare. It was, therefore, decided that neither engineering nor medical data as they related to an individual or a rpining company would be revealed to State officials, management, labor, or others outside the Public Health Service or Bureau of Mines. However, following each mine sur- vey, the Bureau of Mines conferred with mine management to re- port general findings. The companies were also advised by letter of the free silica content of settled dust samples from its mine and the spectrographic analysis of a composited ore sample. For medical data, an exception was to be made only when the X- ray film revealed a condition that needed immediate medical at- tention, such as suspected cancer, tuberculosis, or heart disease. In such cases, the employee's personal physician was notified by the Public Health Service, if so authorized by the employee. 5

To assure high diagnostic standards, the roentgenographic films were first screened for quality and unusual pathology by physicians of the Division of Occupational Health, Public Health Service, and then read by a panel of outstanding radiologists in accordance with the International Classification of Radiographs of the Pneumoco- nioses (International Labour Office, Geneva, 1958). A major task of the Interagency Technical Committee was to in- form industry, labor unions, and o$icial agencies of the study plans. To assure acceptance at the national level, meetings were held with officials and representatives of the American Mining Congress and the major national labor unions involved. The labor unions readily agreed to the limitations which were placed on the dissemination of information. Through their communication channels, the na- tional labor unions advised their locals of the proposed investigation. Following these discussions, most of the States in which the studies were to be conducted were visited to discuss the proposal with safety and health officials as well as representatives of the State mining associations. Most of the State mining associations contacted in- dicated willingness to cooperate. Individual contacts were then made with mining companies by a representative of either the Public Health Service or the Bureau of Mines, and in many cases, by a joint approach. The cooperation of the operating companies was generally quite good, although it varied to some extent among the various mining districts. For instance, in the Western States, no company declined to participate in the study. In other parts of the country, a few companies would permit only the environmental investigation, being ~ apprehensive that the medical study might cause some concern among their employees and reopen the que$tion of compensation. i However, since the environmental data would be of limited value unless accompanied by the corresponding medical information, these mines were eliminated from the sample. A small group of mines objected to the conduct of either the medical or the environ- mental examinations. Figure 1.1 shows the States in which the survey was conducted. As an outgrowth of the study, a group of mines in the Lake Super- ~ ior district volunteered to make available to the Public Health Service and the Bureau of Mines the medical and engineering data i obtained in their silicosis control program, which began in 1933. Through the Saranac Laboratory, which conducted the medical pro- gram, serial films on about 5,000 miners were available for study, some covering a period of almost 30 years. These data permitted a detailed analysis of present day and past conditions and were in- valuable in relating the development and progression of silicosis to a dust control program. 6

Other companies volunteered their mines for more detailed en- I vironmental studies on particle size, effectiveness of various en- ~ gineering control methods, the relationship of airborne silica to the ~ silica content of the settled dust, and medical data which were needed to supplement the present study. The 67 underground mines in the environmental study included '; 14 iron mines with 4,231 employees, 11 copper miries with 7,260 em- i ployees, 22 lead-zinc-silver mines with 4,281 employees, a miscel- laneous group of 12 mines with 4,365 employees, and 8 uranium j mines with 373 employees. Since it was necessary to limit the mag- nitude of the study, open pit mines were not included. r REFERENCES.• 1. Cummings, D. E. Dusts in Atmosphere: Methods of Estimation and Si9nifi- cance. Second Saranac Symposium on Silicosis. B. E. Kuechle, ed. Wausau, Wis. : Employers Mutual Liability Insurance Co., 1935. 2. National Silicosis Conference. Summary Reports Submitted to the Secretary of Labor by Conference Committees, Feb. 3, 1937. U.S. Department of Labor Buli. No. 13. Washington: U.S. Government Printing Office, 1937. (Out of print. ) 3. Doyle, H. N., and others. Accomplishments in the Epidemiologic Study of Silicosis in the Unite$ States, A.M.A. Archives of Industrial Health 12: 48-55, July 1955. 4. Trasko, Victoria M. Some Facts on the Prevalence of Silicosis in the United States, A.M.A. Archives of Industrial Health 14 : 379-386, October 1956. 5. Russell, A. E., and others. The Health of Workers 'in Dusty Trades. 2. Exposure to Siliceous Dust (Granite Industry). Public Health Bull. No. 187. Washington: U.S. Government Printing Office, 1929. (Out of print. ) 6. Russell, A. E. The Health of Workers in Dusty Trades. 7. Restudy of a Group of Granite Workers. Public Health Bull. No. 269. Washington: U.S. Government Printing Office, 1941. (Out of print.) 7. Hosey, A. D., and others. Control of Silicosis in Vermont Granite Industry- Progress Report. Public Health Service Pub. No. 557. Washington : U.S. Government Printing Office, 1957. 8. Mine Safety (Metallic and Nonmetallic Mines) : Hearings (and Report) before the Committee on Education and Labor, Souse of Representatives, 84th Congress. Washington: U.S. Government Printing Office, 1956. 1 A u I 9 8

r CHAPTER II = Summary, Conclusions, and Recommendations SUMMARY A revaluation of the prevalence of silicosis in the metal mining industry of the United States was carried out by the Division of Occupational Health, Public Health Service, Department of Health, Education, and Welfare, and the Bureau of Mines, Department of the Interior, between March 1958 and September 1961. The study was an outgrowth of hearings before the Committee on Education and Labor, House of Representatives, 84th Congress, Washington, D.C., December 1956. - At the turn of the century there was a growing awareness of the problem of silicosis and frequently associated tuberculosis among workers in the dusty trades in this country. During subsequent years a series of studies was initiated to define the problem and institute control programs. Included in this series was a number of studies of silicosis in the metal mines. These metal mine stud- ies showed that massive dust exposures often were encountered and that scarcely any of the employees were free of harmful dust expo- sure. When the dust had a high free silica content, employees ex- posed to massive levels developed severe silicosis within a few years. It was common to find silicosis in 30 to 80 percent of the employees of specific mines studied. In these early studies, up to 60 percent of the employees with silicosis also had tuberculosis. In the mid-1930's a large part of the metal mining industry insti- tuted major dust control practices. World War II, however, im- posed major difficulties in the followup and development of these practices. The war also curtailed the attention given to research and studies on silicosis in metal mines. This and other postwar problems resulted in a dearth of information on the subject. In 1954 the Public Health Service began a revaluation of silico- sis as an occupational disease problem. This consisted first of a study of compensation and other records of official agencies to de- termine the magnitude of the silicosis problem. During a 5-year period, 1950-54, 10,362 cases of silicosis had been compensated or 11 11 I

reported in 22 States from all industries. The silicotic population was primarily an older group with 75 percent of the cases being 50 years and older. Of 3,455 persons for whom reasonably adequate employment histories were available, only 10 percent allegedly re- ceived their entire dust exposure after 1935. The total mining in- dustry contributed two-thirds of all the cases; metal mining accounted for 24.5 percent of these cases. A revaluation of the granite cutting industry in Vermont in 1.956 revealed that the dust concentrations at the time of the survey were well below 5 million particles per cubic foot of air, and that records revealed no cases of silicosis among the granite workers whose initial exposure fol- lowed the installation of dust controls in the mid-1930's. Consequently, at the start of this study (1958-61), it was not known whether the present prevalence of silicosis in the metal mines resulted from a reservoir of miners still working who had significant exposures before dust control practices were instituted, or was due to the lack of application of dust control practices or to inadequate standards. The medical phase of the study was conducted by the Division of Occupational Health of the Public Health Service and the environ- mental phase by the Bureau of Mines. The environmental study included 67 underground mines employing approximately 20,500 persons-14,000 of whom worked underground and 6,500 in surface occupations. At the time of the study this group represented more than 50 percent of the working population of underground metal mines in the United States. The medical study included employees from 50 of the above 67 metal mines and a large number of uranium mines. The mines included in the study represented virtually all metals mined in commer, cially significant quantities in the United States and represented all principal mining methods. Only under- ground mines employing 20 or more men were studied. The study was the most extensive thus far undertaken in the metal mining industry of the United States. ENVIRONMENTAL~,S.TUDY In the environmental study particular emphasis was placed on evaluation of airborne dust in mine working areas. Observations were made also of pertinent factors such as dust control methods, ventilation, methods of working, and air quality. Mine dust must have three characteristics to be capable of pro- ducing silicosis: (1) it must contain crystalline silicon dioxide, such as quartz, (2) it must be in the respirable particle-size range, and 12 (3) it must be present in sufficient concentration. Thus, in a mine program for prevention of silicosis, the variable which lends itself to control is (3) -the concentration of dust. Determination of the alpha-quartz content of the host rock in the various mining areas studied indicated a range from less than 1 per- cent to 95 percent. Dust exposures were evaluated for the mines studied on the basis of the quartz content of 234 samples of settled dust collected from mine working areas. Quartz in the settled dust ranged from less than 2 percent to 95 percent. In 55 percent of the mines the settled dust contained less than 20 percent quartz; 39 per- cent of the mines were in the range of 20-50 percent quartz; and 6 percent of the mines were above 50 percent quartz. Particle-size characteristics of 481 samples of airborne dust were determined by optical microscopy, using the oil immersion technique. Median particle diameter was 0.36 micron. Comparison of particle- size characteristics on split samples using both optical and electron microscopy indicated that there was not a preponderance of sub- micron particles below the range detectable by optical microscopy using the oil immersion technique. Little difference was found in size properties of airborne dust produced in the various mining op-~ erations. All determinations indicated ranges of size of particles capable of significant retention in the alveolar spaces of the lungs. The impinger was used as the principal instrument for sampling airborne dust throughout the environmental study. The threshold limit value for industrial dust currently recognized in the United States is based upon determination. of airborne dust by use of this instrument. Furthermore, the impinger has been employed as the dust-assessing instrument in previous studies, dating back more than 25 years, in which the health status of workers has been cor- related with their occupational exposure to dust. Thus, its use in this study permitted comparison of overall findings with results of previous studies. In discussing results of the study, the threshold limit value for siliceous dust adopted by the American Conference of Governmental Industrial Hygienists' as acceptable for occupational exposure was used as a guideline for evaluating the concentrations of airborne dust as determined in the study. The threshold limit values in effect during the period of the study, 1958-61, had been recognized since the mid-1940's. In 1962, however, the American Conference of Gov- ernmental Industrial Hygienists (ACGIH) adopted a new threshold limit value for dusts containing silica. Results of the study were considered in respect to both sets of threshold limit values. Neither of these sets of values were used, however, as sharp lines of dis- tinction between safe and unsafe conditions, but merely as base lines or reference points for comparison of observed conditions. 13 t

The threshold limit value is applicable to the interpretation of daylong integrated, or "weighted average," exposures. Although the threshold limit value is not applicable to single samples, it is convenient to have some means for their classification. Individual samples of airborne dust that could contribute significantly to weighted average exposures that would exceed 1962 ACGIH thresh- old limit values are considered as containing "excessive dust." It is emphasized that the working environment as assessed, repre- sented conditions existing only at the time of the sampling; the re- sults may not be interpreted as representative of past or future conditions. A total of 14,480 impinger samples was collected in underground working places. Of the samples, 75.6 percent were in the range of 0-5 million particles per cubic foot of air (mppcf) ; 19.3 percent in the 5-20 mppcf range; 3.9 percent in the 20-50 mppcf range; and 1.2 percent over 50 mppcf. An additional 357 samples were collected in intake and return airways not considered as occupied working places. Of the grand total 14,837 impinger samples collected under- ground, 1,440, or 9.7 percent, contained excessive concentrations of dust. During the study 789 full-shift weighted average exposures were determined to provide an evaluation of specific underground opera- tions. These determinations applied only to operations, as such, and were not intended to classify the total underground mining popu- lation into various degrees of dust exposure. Based upon the thresh- old limit value that was in effect during the study, 44, or 5.6 percent, of the weighted average exposures exceeded the limit; whereas, on the basis of the 1962 threshold limit value, 104, or 13.2 percent of the weighted averages, were above the threshold limit value. Distribu- tion of weighted averages that exceeded the threshold limit value was not uniform among the 67 mines studied. In relation to the threshold limit value in effect between 1958-61, none of the weighted averages determined in 46 mines exceeded the limit. In relation to the 1962 threshold limit value, 30 mines had no weighted averages above the limit. Among the other mines the number of weighted averages above the threshold limit value var- ied from one per mine to five or more per mine. It was notable that a few mines contributed a major portion of the weighted aver- age exposures that exceeded the limit, indicating need for more overall attention to the dust control programs at these mines. It is emphasized also that in every mine studied some individual im- pinger samples contained excessive dust, indicating need for im- proved dust control at these particular locations. A comparison of dust concentrations obtained at a group of lead- zinc mines in the Western States with dust concentrations obtained 14 in Utah lead-zinc mines in 1939, indicated very substantial improve- ment in dust control during the years intervening between the stud- ies. Dust concentrations for comparable occupations underground had been reduced at least 80 percent, and in some instances as much as 90 percent. Dust concentrations for comparable occupations on the surface had been reduced a minimum of 50 percent, and in some cases as much as 90 percent. MEDICAL STUDY Medical examinations, including medical histories and symptoms, occupational histories and chest roentgenograms were completed on a total of 14,076 currently employed metal mine workers. Two simple pulmonary function tests were performed by each partici- pant unless maximal respiratory exertion was thoughtt by the team physician to be contraindicated. Participation in the survey was on a voluntary basis, but every effort was made by the Public Health Service working with com- pany and union officials to examine all mine employees. The re- sponse varied widely from 50 percent to 100 percent, the overall average being 77 percent for the 50 nonuranium mines included in the study. In nine mines 90 percent or more of the employees participated and, of these, three small mines had 100-percent participation. - Of the 14,076 chest roentgenograms taken, 476 or 3.4 percent were classified as consistent with a diagnosis of silicosis. Of these, 305 were classified as simple silicosis and 171 were classified as com- plicated silicosis. Although the overall prevalence rate for the study was 3.4 percent, the prevalence varied greatly, ranging from 12.9 percent in one mine to zero in seven mines. Thirteen mines had a prevalence. rate of less than 1 precent silicosis while five mines had more than 7 percent. This overall silicosis prevalence rate of 3.4 percent was in marked contrast with rates revealed by earlier studies of silicosis among metal mine workers conducted in various areas of the country be- tween the years of 1914 and 1935. In some of these early studies more than 60 percent of the workers were found to have roentgen- ologic evidence of silicosis, and the prevalence rate seldom was less than 25 percent. Silicosis in the 1958-61 study, for the most part, was confined to the older miners with more than 15 years of metal mining experi- ence. Silicosis was not observed in the chest film of - any miner under 35 years of age, and only seven cases, or 0.4 percent, were found in the 35-39-year age group. Beginning with the 40-44-year 15 707-103 0-6 -3

age group with a prevalence rate of 2.4 percent, there was a mod- erate increase in the rate with each succeeding age group until it tended to level off at about 12 percent for men from 55 to 64 years of age. Of 63 men examined who were 65 years or older, about one-third were silicotic. In relating silicosis to years of work at the mines, no cases occurred with less than 5 years of exposure. Seven cases, or 0.2 percent, oc- curred in workers with 5-9 years of exposure. Thirty-five cases, or 1.4 percent, occurred with 10-14 years of exposure and 58 cases, or 3.0 percent, occurred with 15-19 years of exposure. After 20 years of exposure the prevalence rates rose rapidly in 5-year incre- ments from 7.6 and 12.1 percent up to an average rate of about 17 percent for the four exposure groups working 30, 35, 40 and 45 years and over. A past history of pulmonary tuberculosis was reported quite in- frequently by this employed mining population, being well under 1 percent in the large nonsilicotic population and reaching only 3.8 percent in the silicotic groupings. An evaluation of the case histories and a recheck of the related X-ray film interpretations, moreover, showed that some of these histories could not be proven, as rela- tively few showed definite evidence of past pulmonary infection. On the other hand, actual X-ray evidence of past tuberculous infection as shown by review of all the chest films was found in 0.6 percent of the total nonsilicotic and 5.3 percent of the silicotic population, a low rate as compared with earlier studies of silicosis and tuberculosis. Information on other illnesses was solicited in the medical history which was obtained from each worker examined. A history of pneu- monia was reported by about one-fifth to one-fourth of all employees, increasing slightly with age. Pleurisy was reported somewhat less frequently than pneumonia, especially among the nonsilicotic em- ployees. Bronchitis was reported in a small percentage of all em- ployees, increasing very slightly with age and showed only a small increase in prevalence among the silicotic workers. Asthma was reported in about 4 to 6 percent of all employees in both the silicotic and nonsilicotic groups. Shortness of breath was reported by less than 5 percent of the non- silicotic miners under 35 years of age, but gradually increased to 18.4 percent among miners 55 years of age and over; for the same age groups, shortness of breath was reported twice as often in the silicotic population. It was more prevalent among persons with complicated than those with simple silicosis. There were only slight differences in the prevalence of shortness of breath at the various elevations of the mines. 16 A history of lead poisoning and mercurial poisoning was reported very infrequently as compared with previous studies. If only men working at mines producing lead in the present study are considered, there were 26 workers or 0.7 percent who reported lead poisoning at any time in the past. In the entire study 23 cases of mercurial poisoning were reported by the miners interviewed. Among 309 employees at mercury mines, 7 said they had been affected at some time with mercurial poisoning. So far as possible, each employee was classified according to his principal occupation. This generally was the broad occupational group in which he had spent more than half of his working life in the metal mining industry, regardless of his present occupation which might have changed in recent years.* All men, however, who had spent 10 years or more at the working face of the mines were classified as "faceworkers." Over one-half of all silicosis cases occurred among men who were classified as faceworkers. With 10-19 years of mining employment they showed a silicosis prevalence of 3 percent which rose to 19 per- cent among men working 20 years or longer. Smaller, but signifi- cant silicosis rates were also found among employees with more than 20 years of employment in other underground operations, sur- face maintenance and construction work, and surface mill operations. Surface transportation and miscellaneous surface operations showed very few cases of silicosis. Silicosis was often found at the time of the survey among older surface workers who had previously spent many years underground, but had been transferred to surface opera- tions for various reasons. The mines were divided according to the size of their working population and the prevalence of silicosis in each mine was expressed as the percentage of employees so affected. There was little rela- tionship between the size of the mines and the prevalence of silicosis. Attention was also directed toward the question as to whether the silicosis found at a metal mine was attributable solely to employ- ment at that mine or to• a combination of work experience at several mines. A comparison of silicosis rates for groups of employees who had experience in one mine only, and for groups of employees with experience in two or more mines, showed little difference when similar occupations and periods of exposure were compared. The prevalence of silicosis was slightly greater among 'employees with experience in two or more mines. *This tabulation does not include uranium miners, many of whom could not be classified by principal occupation, and workers at seven iron and lead-zinc mines situated in low free silica limestone formation, who were found to have a negligible prevalence of silicosis in all occupations. 17

The prevalence of silicosis among workers in mines producing iron, lead-zinc, copper, uranium, and miscellaneous commodities was determined by each commodity. There was no great differ- ence in the pattern of silicosis prevalence which could be attributed to the difference in commodities. Men having had 5 or more years of exposure in other dusty trades in addition to the metal mining industry, were excluded from the study group because of the possibility that the prevalence of silico- sis in such a mixed exposure group would be unduly influenced by other dusty employment. Among this mixed exposure group it was noted that, when the total duration of employment in dusty trades was approximately the same, the silicosis prevalence rates were very similar to that of metal mine workers included in the study. It thus appears that the exclusion of 671 workers from the study group because of previous exposure in other dusty trades did not appreciably alter the results of the study. In general, great advances have been made by the metal mining industry in controlling the silicosis hazard, beginning about the mid- 1930's. The effects of these dust control measures would not have been evident until many years later, because of the reservoir of miners exposed to dust prior to this period. Fortunately the 1939 Study of Non-Ferrous Metal Mine Workers in Utah presented data which may be contrasted with data from a group of 12 western lead-zinc mines investigated during the present survey (1958-61). The overall prevalence of silicosis was found to be 40 percent lower than in the earlier study. Even more striking was the reduction of 80 percent in the silicosis rate among persons employed in the mines less than 10 years and 73 percent for the group employed 10-19 years. The environmental data of the 1958- 61 survey also showed a very favorable trend in reduction from the at- mospheric dust levels found in the 1939 Utah survey. An analysis was also made of comparative prevalence rates within the 1958-61 study for silicosis among metal mine workers who had worked in the industry only since 1935 or later, and those who had some portion of their employment before 1935 as well as later, excluding those at seven mines located in low free silica limestone formations. This permits some comparison of silicosis prevalence rates among workers within this study who had substantial expo- _ sure before dust control measures became widely used, and those employed only during the subsequent 25 years or so. Among the relatively small group of miners with some mining experience be- fore 1935, but who had worked in metal mines a total of only 10-14 years, the silicosis rate was 6.1 percent; a group of 1,818 miners who had worked the same number of years but only in 1935 or later had a rate of 1.5 percent. Figures for persons with 15-19 years in metal mines showed 8.3 percent with silicosis in the pre-1935 group and 3.3 percent with silicosis in the after-1935 group. After 20-24 years in metal mining, men with experience prior to 1935 had a silicosis prevalence of 12.7 percent compared with 7.2 percent for miners with experience during or after 1935. This is a trend similar to that shown in comparing the present study with the 1939 Utah study. A special study was made of the records of a group of metal mine workers from one iron mine which had a continuous silicosis con- trol program underway since 1933. Beginning with the records of that year it was possible to examine X-ray films of all workers then employed and others as they were hired and to follow the entire group year by year as serial X-ray films were taken throughout the 28-year period. Complete work records were also . available for analysis. Among the 1,293 men included in this study, 410 had worked be- fore 1933, and thus had been exposed before the improvement in the mine environment. Silicosis was found at the time of first X- ray examinations in 1933 in 83 men, and 16 men who were negative in 1933 developed silicosis later. Among the 883 men who were first employed after the control program began in 1933, there was not a single case of silicosis which developed even in a substantial group with more than 20 years of exposure. Only 6 percent of the men with silicosis showed any progressive change in the disease as they continued mining employment. CONCLUSIONS Prior to the beginning of this study it was known that in recent years substantial numbers of men who had been employed in the metal mining industry were awarded disability compensation for silicosis. With silicosis, thus known to occur in the industry the study was designed to determine the prevalence of silicosis among the work force of the industry, to define present day environmental conditions, and to seek answers to the questions : 1. Are the cases presently occurring the result of pre-control exposure, in view of the long latent period for the develop- ment of silicosis ? 2. Are they the result of failure to apply dust controls univer- sally 1 3. Are cases occurring because of inadequacy of standards for acceptable levels of dustiness in use since 1935 ? 18 1 19

THE WORKING ENVIRONMENT 1. Each mining company should maintain a dust monitoring program conducted or supervised by a person competent in the techniques of dust sampling and interpretation of results. a. For determining levels of exposure, dust samples should be taken in the breathing zones of workmen. b. The program should be conducted in such a manner that it will detect changes in environmental condi- tions and promptly locate conditions in need of correction. c. Accurate and complete records of dust conditions should be kept. These should be tabulated, analyzed, and reported to a responsible level of management at regular intervals. 2. Proper methods of dust control should be initiated promptly when the need is discovered. a. Adequate ventilation by mechanical means should be provided at all working places. b. Recirculation of air should be held to a minimum consistent with good mining practice. c. All ore and broken rock should be thoroughly wetted to reduce dust during subsequent handling operations. d. All dust control devices and materials handling equipment, both underground and on surface, should be frequently inspected and maintained in proper working condition to limit to the lowest prac- ticable level the generation or dispersion of dust. e. Men should not be permitted to reenter a workplace after blasting until sufficient time has elapsed' for dust and gases to be reduced to a safe level. 3. Workers should be informed of the dust hazards associated with their job, the methods employed for the control of dust exposure, and instructed in good work procedures to minimize dust dispersion and in the proper use of equip- ment. All employees should give their full cooperation in helping to maintain an effective dust control program. 4. Mining companies should request, whenever necessary, the assistance of the Bureau of Mines or other qualified agen- cies in instituting and evaluating dust monitoring and dust control programs. MEDICAL SERVICES 1. Medical examinations a. All men entering the metal mining industry should have a preplacement physical examination includ- ing a technically satisfactory X-ray film of the chest, b. Periodic physical examinations including an X-ray chest film should be performed annually on under- ground workers, and biennially on surface workers in order to detect early silicotic changes, evidence of active pulmonary tuberculosis, or other pulmo- nary disorders. c. No worker should be denied employment for which he is trained because of simple silicosis but rather he should be permitted to work in an environment with effective dust control that would be safe both for him and his fellow workers. d. Any employee found to have active pulmonary tuber- culosis should be placed under treatment and should not be permitted to resume employment at a dusty occupation: Workers with minimal, arrested, or healed reinfection tuberculosis should be allowed to continue to work, but should observe the same precautions as the man with simple silicosis. Healed primary tuberculosis does not seem to be a con- traindication for employment in a dusty trade. 2. Health supervision and practices : Although the following recommendations were not developed directly as a result of the 1958-61 silicosis study, they represent standards of good practice and for the most part result from previous studies of the Public ublic Health Service and the Bureau of Mines. a. Close medical supervision is desirable for all em- ployees in order to prevent or control ordinary res- piratory infections, and other common illnesses. During the course of medical examinations and day- to-day visits to the hospital or clinic, employees should be advised on various aspects of hygiene and preventive medicine. b. Employees returning to work after an absence due to an injury or illness should be cleared through the medical service to insure their being physi- cally fit for their jobs, thereby protecting their own and their coworkers' health and safety. 23

c. The mine physician, whether full or part time, should be familiar with the various mining operations and their potential health hazards and should make pe- riodic sanitary inspections. The official health de- partment should be informed of any conditions requiring technical or specialized assistance. Also, the physician should be in close communication with plant safety and dust control personnel. d. All mines should provide conveniently located change houses with facilities for hot and cold shower baths, and lockers and drying rooms for work and street clothing. e. Records of all absenteeism due to illness or injury should be kept by the mine medical department indi- cating the course, nature, duration, and outcome of such disability. These records should be tabulated and analyzed in a monthly report to serve as a basis for study and corrective measures to promote em- ployee health and minimize such absenteeism. I 24 1 25

CHAPTER III Review of Past Studies A review of past studies reveals the scope and severity of the sili- cosis problem in the metal mines of this country during the first four decades of this century and of the efforts through environmen- tal and medical measures to control the problem. A general aware= ness of the severity of silicosis and tuberculosis among workers in the dusty trades became apparent at the turn of the century. The equally apparent high prevalence of "miner's consumption" and tuberculosis among metal miners drew attention to the need for studies in the mines and the institution of control measures. The first major investigation of silicosis in the metal mines in the United States was made in the Joplin, Mo., mining district in 1914- 15 through a cooperative study by the Bureau of Mines and the Public Health Service.l * Of a total of 93 miners examined, 64, or 68.8 percent showed definite evidence of pulmonary disease. Of these 64 miners, 39 had the classical symptoms of pulmonary tuber- culosis. Environmental studies showed that the miners were ex- posed to massive dust concentrations arising from such operations as blowing of dry holes, squibbing, boulder popping, dry drilling, and dry handling of the ore. Atmospheric dust concentrations as high as 6 to 7 milligrams per 1001iters of air were common. To further define the silicosis problem among miners in this dis- trict, a more comprehensive study was made in 1915? Of 720 miners examined, 472 or 65.5 percent had silicosis. Of the 472 miners with silicosis, 21.8 percent also had pulmonary tuberculosis. The en- vironmental study bore out the extreme dustiness of the various operations found during the previous study and further revealed that the chert in the mines contained free silica ranging from 70 to over 95 percent. During 1916-19, the Bureau of Miness and the Public Health Serv- ice conducted a cooperative study of the prevalence and cause of miner's consumption in the Butte, Mont., district 8 Of 1,018 miners examined, 432 or 42.4 percent showed definite signs of dust injury to the lungs. Of the 432 miners with silicosis, 14.6 percent also had pulmonary tuberculosis. The environmental data revealed that *Numbers refer to the reference list at the end of the chapter. I 1 a i 27

the Butte mines in general were more dusty than the Joplin dis- trict mines but that, in contrast, the dust of the Butte mines con- tained only 50 to 60 percent free silica compared to the over 90 percent free silica of the dust in the Joplin mines. An examination of 303 gold miners in Nevada in 1921' showed that 80 percent had silicosis. During the same year an examination of 181 gold miners in California showed that 25 percent had silicosis. In 1923 6 the mining companies of the Tri-State District of Okla- homa, Kansas, and Missouri, in cooperation with the Bureau of Mines and the Public Health Service, conducted a study of the mines in the district to determine whether the measures in use for the prevention of silicosis were adequate, and, if not, to recommend improvements. Of 309 miners examined, 94, or 30.4 percent, had definite silicosis, and an additional 114 were classed as doubtful. The investigation showed the mines of the Picher, Okla., district to be less dusty than those of the Joplin district. It was pointed out that the practices in the Picher mines had improved as a result of the Joplin study and recommendations. Recommendations to the mining companies in- cluded yearly medical examinations of all miners. This study led to the establishment of a clinic in Picher, cooperatively operated by the Bureau of Mines, the Public Health Service, Metropolitan Life Insurance Co., and the Tri-State Zinc and Lead Ore Producers Association.6 Of the 27,553 individuals examined during the period 1927-32, 5,366 or 19.4 percent, had silicosis. Of the 5,366 with silicosis, 742 or 13.9 percent also had pulmonary tuberculosis. On April 14, 1936, the Secretary of Labor, recognizing the con- fusion which existed at the time regarding silicosis, called the First National Silicosis Conference.7 After a general discussion, the con- ference agreed to organize four committees to do at least three things: (1) study specific phases of the silicosis problem; (2) as- semble -in a series of reports the essential facts about silicosis; and (3) present specific suggestions for silicosis prevention and for straightening out other difficulties that silicosis had created. The reports of the committees served to clarify many aspects of the problem by defining the etiology of the disease, its relationship to tuberculosis, and the medical and engineering control methods. The conference was doubtlessly a motivating factor for silicosis control in the mining industry as well as other dusty trades. During the period 1935-37, many of the larger mining companies in the Coeur D'Alene Mining District of Idaho started routine pre- employment and periodic physical examinations of miners. Of 6,243 miners exposed to silica dust,8 2,328 miners or 37.3 percent had sil- icosis; 1,967 or 31.5 percent were classed as doubtful or presilicosis; 145 or 2.3 percent had both silicosis and pulmonary tuberculosis. Average dust levels encountered during rock drilling, crushing, i , mucking, drawing chutes, and in airways ranged from 3.7 to 36.0 with an overall mine average (278 samples) of 16.7 million parti- cles per cubic foot of air. In 1939 the Utah State Board of Health collaborated with the Pub- lic Health Service and the Utah State Industrial Commission in a study of nonferrous metal mine workers.® Of 727 miners examined, 66, or 9.1 percent, had silicosis and 42, or 5.8 percent, had border- line silicosis. Nine, or almost 14 percent, of the workers with sili- cosis also had pulmonary tuberculosis. Environmental data from the Utah survey showed that the under- ground worker was exposed to weighted average dust levels rang- ing from 3.8 million particles per cubic foot of air for station tender and carmen to 23.1 for miner, driller, and mucker, and 37.5 for bin tender, carloader, and chute gate tender. The median parti- cle size as determined by impinger samples was 0.94 micron. Less than 1 percent of the metal miners were exposed to average dust concentrations higher than 30 million particles per cubic foot of air. Around 86 percent were exposed to dust concentrations between 6 and 30 million particles per cubic foot of air and around 12 percent were exposed to less than 6 million particles per cubic foot of air. It appeared that the average underground worker was exposed to atmospheric dusts containing 20-40 percent free silica. A num- ber of methods had been instituted for minimizing the silica dust hazard including wet drilling, wetting of the muck piles, good under- ground ventilation, local exhaust ventilation, and good operational practices. It was observed that good practices in the proper use of the above methods to minimize dust reduced the dust levels 5-fold to 50-fold under levels existing during poor practices. Data relating to 727 metal mine workers in the 1939 Utah study were grouped according to weighted average dust concentration in arbitrary intervals of 6 million particles per cubic foot of air. Each of these five dust concentration groups was subdivided into three dura- tions of employment in metall mines, namely, less than 10 years, 10-19 years, and 20 years and over. There were no cases of silicosis in 39 miners who had worked at average dust levels under 6.0 million particles per cubic foot of air. Workers exposed to dust concentra- tions of 6.0-11.9 million particles showed no case of silicosis for the 44 men who worked less than 10 years, 1 case among the 36 men with 10-19 years, and 2 cases among the 18 men with service of 20 years and over. A study of employee work histories in this group indicated that dust exposures were likely very much higher for varying pe- riods than the ranges shown here. Among persons exposed to 12.0- 17.9 million particles the percentages with silicosis were 0, 7.0 and 19.0, respectively. With dust exposure of 18.0-23.9 million parti- cles, silicosis increased markedly and was found in all duration 28 29

groups, progressing from 0.5 percent for those with less than 10 years, to 19.6 percent for 10-19 years, and 37.0 percent for 20 years and over. The highest exposure group, 24.0 and over million particles, showed silicosis prevalence of 3.4 percent, 18.4 percent, and 68.2 percent. In following up the recommendations of studies made in the Tri- State Mining District of Oklahoma, Kansas, and Missouri during the period 1917-32, the Tri-State Zinc and Lead Ore Producers Associa- tion in 1936 employed an air hygiene engineer to conduct routine dust counting surveys in companies desiring this service. Included in dust control measures in the mines were : wet drilling, wetting the muck and workfaces before shoveling and drilling, wetting of haulageways, blasting at the end of workshift, and ventilation.~ During the first 4-year period, the air hygiene engineer took over 4,000 air samples for dust.10 Seventy-six percent of the dust samples collected during the first year were under 5.0 million particles per cubic foot of air. During the fourth year 88 percent of the samples were under 5.0 million particles. Since not all the companies were using the services of the air hygiene engineer, a survey was made during the fourth year to determine whether there was a difference in the degree of mine dustiness based upon whether or not routine dust sampling was done in the mine. Drillers, shovelers, and drag operators had respective average dust levels of 1.6, 2.2, and 2.4 mil- lion particles per cubic foot of air in mines conducting routine dust sampling compared to respective averages of 6.6, 4.3, and 7.4 for mines without routine dust sampling services. This clearly points out the usefulness of routine monitoring of dust levels in the mines since it offers a check on proper and efficient use of dust control measures. The onset of World War II greatly curtailed the attention given to research concerning the problem of silicosis among metal mine workers. This resulted in a dearth of published information on this subject between that period and the start of the current study. REFERENCES 1. Lanza, A. J., and Edwin Higgins. Pulmonary Disease Among Miners of the Joplin District, Mo., and Its Relation to Rock Dust in the Mines. Bureau of Mines Tech. Paper 105,47 pp., 1915. ( Out of print. ) 2. Higgins, E., A. J. Lanza, F. B. Laney, and G. S. Rice. Siliceous Dust In Relation to Pulmonary Disease Among Miners in the Joplin District, Mo. Bureau of Mines Bull. 132, 116 pp., Washington: U.S. Government Printing Office, 1917. (Out of print. ) 3. Harrington, Daniel, and A. J. Lanza. Miners Consumption in the Mines of Butte, Mont. Bureau of Mines Tech. Paper 260, 19 pp., 1921. (Out of print. ) 4. National Silicosis Conference : Final Report of the Cominittee on the Pre- vention of Silicosis Through Medical Control. U.S. Dept, of Labor Bull. No. 21, Pt. I, Washington: U.S. Government Printing Office, 1938. (Out of print. ) 5. Sayers, R. R., F. V. Meriwether, A. J. Lanza, and W. W. Adams. Sili- cosis and Tuberculosis Among Miners of the Tri-State District of Okla- homa, Kansas, and Missouri. I. For the Year Ended June 30, 1928. Bureau of Mines Tech. Paper 545, 30 pp.,1933. (Out of print.) 6. Merlwether, F. V., R. R. Sayers, and A. J. Lanza. Silicosis and Tuber- culosis Among Miners of the Tri-State District of Oklahoma, Kansas, and Missouri. II. For the Year Ended June 30, 1929. Bureau of Mines Tech. Paper 552, 28 pp.,1933. ( Out of print. ) 7. National Silicosis Conference. Summary Reports Submitted to the Secre- tary of Labor by Conference Committees, Feb. 3, 1937. U.S. Depart- ment of Labor Bull. No. 13, Washington : U.S. Government Printing Office, 1937. (Out of print.) 8. Ellis, P. M., M. T. Smith, H. E. Bonebrake, and L. B. Hunter. Silicosis. General Considerations and Survey in the Coeur D'Alene Mining Dis- trict of Idaho. North We8t Medicine, Vol. 41, p.,406, December 1942. 9. Dreessen, W. C., R. T. Page, J. W. Hough, V. M. Trasko, J. L. Jones, and R. W. Franks. Health and Working Environment of Non-Ferrous Metal Mine Workers. Public Health Bull. No. 277. Washington: U.S. Government Printing Office, 1942. 10. Dills, C. C. Study of Dust Conditions In the Tri-State Mining District of Oklahoma, Kansas, and Missouri, American Journai of Publio Health 31: 619-626, June 1941. t 30 31 707-103 07,64-4

CHAPTER IV T'he Enviromental Study Part A-Field Investigation PURPOSE AND SCOPE The purpose of the engineering phase of the study was to assess the working environment in a representative segment of the Nation's un- derground metal mines, with particular attention to airborne dust. - When the study was started in the spring of 1958, approximately 85,000 men were employed at 2,000 underground metal mines in the i,Tnited States. About 25,000 men were employed underground, and 10,000 were employed in associated surface areas such as shops, crushers, mills, and other locations. The environmental study, which was completed in the fall of 1961 included 67 mines chosen on the basis of characterizing factors such as commodity, geology, mining district, mining method, and size. These mines were operated by 46 different companies and represented em- ployment of approximately 14,000 underground and 6,500 surface workers. Thus, although the number of mines included in the study was only a small fraction of the n}ines operating at the time, the number of men employed at these mines represented almost 60 per- cent of the nationwide employment at underground metal mines. Table IV.1 presents data on the mines included in the study.' TABLE IV.1.-Data on mines included in the dust study-_ - Commodity group Mines Underground employees surfaae employees Total employees Totai-------------------- 67 14,010 6,500 20,510 Iron--------------------------- 14 3,267 964 4,231 Copper------------------------- 11 5,072 2,188 7,260 Lead-zinc•silver------------------ 22 3,260 1,021 4,281 Uranium----------------------- 8 325 48 373 Misceiianeous------------------- 12 2,086 2,279 4,365 i

Data collected in the underground study included determination of concentrations of airborne dust, particle-size distribution anal- yses, and determination of free silica in samples of airborne and settled dust and dust-source materials. Semiquantitative spectro- graphic examination of these materials was made as a matter of record in the event the data would be needed to explain other find- ings of this or future studies. I)ata were obtained also on dust control methods, ventilation, and composition of mine atmospheres. Measurements of barometric pressure, temperature, and humidity were made as a matter of record, but results are not included in this report. Measurements were made of natural underground ionizing radiation, but since no levels of consequence were observed in any working place, results are not reported. The sampling method was designed basically to indicate the time- weighted average dust exposures of underground employees in the conduct of specific and typical operations. The weighted average exposure represented the average dust concentration, expressed in millions of particles per cubic foot of air (mppcf), to which an employee was exposed over an entire working shift. To make this determination, the workman being observed was followed during the complete shift and samples of airborne dust were collected in his breathing zone at 30-minute intervals. The time-weighted average concentration of all samples was then calculated, taking into account the different activities involved throughout the shift in conducting the observed operation. The procedure may be represented by the' equation- in which Dwa=(d'Xti)-I-(d2Xtz)-I- . . . +(dn.Xtn) T Dwa=full-shift weighted average dust exposure, mppcf d4dZ,da=average dust exposures during each activity comprising the full shift, mppcf t,tZ,t„=time spent in each activity comprising the full shift, hours T=total time of shift, hours =t1-I-ta-}- . . . +t, The underground sampling procedure was designed to obtain enough weighted averages to insure that the study was representa- tive of conditions and operations at each mine. The minimum num- ber of places and operations to be sampled in a mine was based upon the following criteria : 1. At least 20 percent of all locations at which ore or waste was produced. 2. At least two of each type of working place. For example, if four drifts were working, at least two (50 percent) would 34 be sampled. If three raises were working, at least two (66.7 percent) would be sampled. If only two stopes were operating, both would be sampled. As a result, the small- er mines usually would yield a larger number of samples in proportion to number of employees than would the larger mines. In several of the smaller mines every ore-produc• ing place (usually only two or three) was sampled. 3. Any other location in which sampling was necessary to ob- tain representative data. In addition to these observations underground, samples of air- porne dust representative of the working environment were col- lected in the surface installations that were considered to be parts of the mine properties. The effects of surface weather conditions were not evaluated because each mine was surveyed but once even though studies were conducted in all seasons of the year. GEOGRAPHY AND GEOLOGY OF ORE DEPOSITS Locations of the mines' included most mining areas of the con- tinental United States. Surface elevations ranged from approxi- mately 500 feet to 11,000 feet above sea level. Most metals mined in the United States were represented in the study. Geologic in- formation was based principally on data received from the mine operators. Table IV.2 relates the host rock with alpha quartz anal- yses. These analyses were used to determine the members of each group in the table. TABLE IV.2.-Host rock and alPha quartz correlation Group Host rock ^ Commodity Alpbaquartz, bulk sample", percent" 1 Andesite, calcite gangue____ Gold, silver_________________ 95 2 Quartzite, quartz monzonite_ Gold, silver, copper, lead, zinc, 21-75 cobalt, molybdenum, mer- cury. 3 Schist, slates, shales------- Gold, silver, copper, lead----- " 4-54 4 High silica limestone, dolo- Gold, silver, copper, lead, zinc, _. 9-67 mite. molybdenum, mercury, iron, . tungsten. 5 Rhyolite, granite---------- Molybdenum, manganese, ,_ 9-6Q mercury. 6 Chert, opalite_____________ Mercury, iron--------------- 2-10 7 Basalt, peridotite---------- Copper, chromium___________ C1-12 8 Low silica limestone__-____ Copper, lead, zinc, iron_______ <1-9 9 Predominately sandstone_ _ _ Uranium, vanadium--------- 42-95 ..

The study included mines producing virtually every metal mined in significant commercial quantities in the United States. No ap- parent relationship was found between dust concentrations and the commodity being mined. MINING METHODS Two or more mining methods, or modifications of methods, fre- quently were used at the same mine; however, one principal stoping method usually was characteristic of each mine. Various mining methods are described in detail by Jackson and Hedges,' * Jackson and Gardner; Peele,g and Bucky.4 Underground operations other than stoping included exploration, development, material handling, transportation, and maintenance. Distribution of mines by principal mining method is shown in table IV.3. TABLE IV.3. Dfstribution of 67 minea according to principal mining method Mining method: Number of minea Block caving------------------------------------------------- 9 Open stopes------------------------------------------------ 6 Sublevel stopes ----------------------------------------------- 9 Room and pillar--------------------------------------------- 16 Shrinkage stopes---------------------------------------------- 3 Cut-and-fill--------------------------------------------------- 10 Square set--------------------------------------------------- 11 Top slicing--------------------------------------------------- 1 Development only-------------------------------------------- 1 Pumping only--------------------------------------------•---- 1 SURVEY METHODS The midget impinger 6 e was the standard instrument used for sam- pling airborne dust. This instrument was used for several reasons: (a) The impinger has been used as the dust-assessing instru- ment in most major studies in the United States in which prevalence of silicosis has been correlated with concen- trations of airborne dust to which workers have been exposed. As these studies date back more than 25 years, and have served in large part as the basis for pro- mulgation of threshold limit values for dust in occupa- tional environments, adherence to use of the impinger in the current study would permit a comparison of results with the findings of past investigations. *Numbers refer to reference list at the end of the chapter. 36 % m M A t a 37 I M aw

While some members of the field party set up a temporary lab- oratory at each mine, others obtained information of a general na- ture, including size of mine, number of employees, production, and other necessary data. After surface and underground working places were observed, sampling locations were selected to represent all routine working conditions. At least 20 percent of each type of underground operation was sampled; in smaller mines a larger per- centage of working places was sampled. All sampling locations were chosen by Bureau of Mines personnel. Midget impinger samples of airborne aust in underground work- ing places were collected either in the workmen's breathing zones or as close as practicable to their breathing zones. These samples were taken generally at 30-minute intervals during the entire shift, and included all activities comprising the operation that the work- man was performing. Results of these samples provided the basis for calculating a time-weighted full-shift average dust exposure re- lating to each operation studied. Three or four midget impinger samples were collected at each surface location where men were employed, and in underground locations such as skip pockets, dumping points, and repair shops. Experience indicated that dust concentrations in these locations did not fluctuate sufficiently to warrant full-shift sampling. At the start of the study approximately 1,300 midget impinger samples were counted in the field laboratory within 24 hours of col- lection, and recounted in the Bureau of Mines Denver laboratory 1 to 3 weeks after collection. Comparisons between field laboratory counts and Denver laboratory counts indicated that the average variation was less than 4 percent. Throughout the study approximately 25 percent of the midget im- pinger samples collected at each location were counted in the field laboratory within 24 hours of collection. At the completion of the survey at each mine, dust concentrations determined from these samples were used as a basis for verbal discussions with mine offi- cials. The remaining samples were counted in the Denver laboratory. A total of 18,079 midget impinger samples of airborne dust was collected; 14,837 underground and 3,242 on the surface. Table IV.4. shows the distribution of the samples in respect to location or operation. In addition to the midget impinger samples, numerous samples were taken for free silica analyses, particle sizing, air quality analyses, and other special data. Table IV.5 lists all samples collected during the study. 40 TABLE IV.4.-Number of midget imginger samples collected for determination of airborne dust concentrations Location or op eration Samples Number Percent TotaL--------------- ----------- ------------ 18, 079 100.0 Stopes-------------- ------- ----------- ------------ 6,701 37.1 Drifts--------------- ------ ----------- ------------ 2,171 12.0 Raises---------------------- ----------- ------------ 899 5.0 Grizzlies----------- ------ ----------- ------------ 120 .7 Underground hoists__________ ___________ ____________ 202 1. 1 Skip and chutes---- -_______ ___________ ___-___--_-- 546 3.0 Motor crews ---------------- ----------- ------------ 1,430 7.9 Exploration drilling__________ ___________ ____________ 205 1. 1 Timbermen---------------- ----------- ------------ 1,149 6.4 Trackmen------------------ ----------- ------------'' 126 .7 Repairmen underground__-_____ __________ ____________ 229 1.3 Gunite and concrete crews unde rground___ ____________ 200 1. 1 Miscellaneous mobile equipmen t undergrou nd__________ 285 1.6 Miscellaneous employees under ground_____ ____________ 114 .6 Maintenance and repair (surfac e)_________ ____________ 1,114 6.2 Crushers (underground and surf ace)_______ ____________ 459 2. 5 Mills (underground and surface )__________ ____________ 1,145 6.3 Assayers------------------- ---------- ------------ 196 1. 1 Hoistmen (surface)___________ __________ ____________ 159 .9 Topmen--------------------- ---------- ------------ 94 .5 Operating miscellaneous equipm ent (surface ) _ _ _ _ _ _ _ _ _ _ _ 23 .1 General air (intake and return a irways) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 368 2.0 General air (surface)__________ __________ ____________ 144 .8 TABLE IV.5.-Samples collected during the atudy Type Number Purpose Total----------------- 19,974 Midgetimpinger_____________ 18,079 Dust concentration _ - Airborne dust________________ 82 Free silica Settled dust__________________ 234 Free silica Bulk (ore)___________________ 82 Free silica Cellulosic filter_______________ 481 Particle size Cellulosic filter_______________ 307 Radiation Vacuum bottle- _____________ 614 Air quality Thermal precipitator__________ 95 Comparison with midget impinger 41-

THRESHOLD LIMIT VALUES Through the years those concerned with the health of workers in industry have endeavored to develop information on concentrations of atmospheric contaminants that may exist in industrial working environments without producing ill effects upon workers as a re- sult of their occupational exposures. Such information has been developed through laboratory research and through studies in vari- ous industries where medical examinations of workers have been used to correlate their health status with the extent of contamination of the atmospheres in which they have worked. Such information has been made available, through various means, to those respon- sible for maintaining suitable working conditions in industry to provide them with guidelines to follow in establishing effective control measures. At the first annual Conference of Governmental Industrial Hy- gienists (now the American Conference of Governmental Industrial Hygienists) in 1938, it was decided that "one of the important ob- jectives of the conference would be to collect and make accessible to all industrial hygiene workers such information and data as might be of assistance to them in proper fulfillment of their duties.716 The first list of maximum allowable concentrations compiled by the conference was presented in 1942, and consisted merely of an assembly of information available at the time. This first list was presented without comment as to the validity of the data. A more formalized list of maximum allowable concentrations or "threshold limit values" was issued by the American Conference of Governmental Industrial Hygienists in 1946?e This list was issued with the definite understanding that it be sub- ject to annual revision, a policy which has been continued by the conference. This list contained the following suggested threshold limit values for mineral dusts : High silica (above 50 percent particles per cubic foot of air. Medium silica (5-50 percent particles per cubic foot of air. Low silica (below 5 percent particles per cubic foot of air. free silica, SiO2)-5 million free silica, SiOz)-20 million free silica, SiO2) -50 million When the study of dust conditions in metal mines was started by the Bureau of Mines in 1958 these threshold limit values were still in effect 17 and were the guidelines suggested to mine managements during the field study. At the 1962 meeting of the American Con- ference of Governmental Industrial Hygienists new threshold limit values were adopted 18 Reasons for the change in threshold limit values are to be publislked by the .A,merican Conference of Govern- mental Industrial Hygienists. These new values were based upon the formula : TLV, mppcf=- 250 %SiOZ+S to express threshold limit values in terms of millions of particles per cubic foot of air. In this formula free silica content refers to airborne dust. The American Conference of Governmental In- dustrial Hygienists emphasizes that the values "should be used as.guides in the control of health hazards and should not be regarded as fine lines between safe and dangerous concentrations. 'They represent conditions under which it is believed that nearly all work- ers may be repeatedly exposed, day after day, without adverse effect. The values refer to time-weighted average concentrations for a normal workday." 18 Both the 1958 and 1962 threshold limit values are' used in this re- port merely as bases or guidelines for subsequent discussions, and are not intended to represent inflexible boundaries or lines of division between conditions found in the mines studied, nor does their use in this report necessarily represent endorsement by the Public Health Service or the Bureau of Mines. The threshold limit values for siliceous dusts suggested by the American Conference of Governmental Industrial Hygienists re- late to time-weighted average concentrations that represent expo- _._ sure throughout a normal workday. The weighted average exposure is derived from the results of multiple samples collected through- out the workday, each sample being weighted according to the pro- portion of the workday that it represents. The sum of these weighted values is the time-weighted average exposure. An indi-, cidual dust concentration determined in such a group of samples cannot be considered, of itself, as being above or below the thresh- old limit value. However, the threshold limit value provides the only logical baseline, or point of reference, for considering the po- tential of each sample in contributing to the weighted average expo- sure. For this reason individual samples that could contribute significantly to weighted average exposures exceeding the 1962 American Conference of GovernmentaI Industrial Hygienist thresh-' old limit value are designated in this report as representing "exces- sive dust." - -- - - In areas where experience demonstrated that dust concentration did not vary significantly throughout the workday, the arithmetic average dust concentration was determined by multiple sampling during the workday. Such arithmetic averages are considered in this report in the same sense as time-weighted averages. 42 ~ _- _- 43 ~ _

I RESULTS OF ENVIRONMENTAL STUDY PARTICLE SIZE Particle-size determinations by optical microscopy were made from 481 cellulosic membrane filter samples, usually collected in the breathing zone of surface and underground workers perform- ing routine operations. Fifty-five of these samples were divided each into two sections, one section being evaluated by the optical microscope, the other section being evaluated by the electron mi- croscope. A microprojector with ruled screen and a 1/12a, 1.32 N.A., oil-immersion objective afforded a total magnification of 10; 000 for optical microscope determinations, with a resolution of about one-fourth micron. Comparative determinations of particle-size distribution were obtained by use of the electron microscope with magnification of 9,000 to 10,000 diameters with a resolution of about 0.005 micron. Table IV.6 shows a comparison of results obtained by optical_and electron microscopy. Statistical correlation between companion geometric mean diameters determined on the same samples by elea- tron and optical microscopy was inconclusive, and the standard deviations yielded by the two methods were seldom in agreement. Nevertheless, the median geometric mean diameter determined for each group of samples by electron microscopy, with a resolu- tion of 0.005 micron, is very near in value to the corresponding me- dian determined by optical microscopy. Thus, even though good statistical correlation between results by the two methods was not found, it can be concluded from the comparison of medians that there was not a preponderance of submicron particles too small to be detected by optical microscopy in the samples examined. - TABLE IV.6.-Comparison of 55 particle-size analyses by electron and optical microscopy Number of Operation Median of geometric means, microg Samples Optical microscope Electron microscope 19 Drilling---------------------------- 0.37 0.33 8 Slushing---•------------------------ .36 .42 7 Mucking--------------------------- .38 .33 4 Air cleaner intake___________________ .39 .64 3 Air cleaner exhaust__________________ ,40 .38 3 Crushing___________________________ .29 . 34 11 Miscellaneous__..____________________ .35 25 45

Table IV.7 shows the frequency of occurrence of ranges of geo- metric mean particle diameters for the 481 samples sized by optical microscopy. Figure IV.2 shows the same data in graphic form. The median geometric mean diameter for the 481 samples was 0.36 micron. Almost 80 percent of the samples yielded geometric mean diameters within the range of 0.26 to 0.45 micron, that is, within ±0.10 micron of the median value; and almost 95 percent of the samples had geometric mean diameters of 0.50 micron or smaller. It is of interest to note that the medians of geometric means determined by optical microscopy for various operations as shown in table IV.6 are, with one exception, within -0.05 micron of the median value for all 481 samples. Standard geometric deviation was quite variable within each range of geometric mean particle diameter as shown in table IV.7. In general, the range of standard geometric deviation decreased with increasing geometric mean particle diameter. The variability from one sample to another of both geometric mean diameter and standard deviation made impractical any effort to predict the con- centration of submicron particles for any operation or group of samples on the basis of particle-size results and impinger counts. In gerieral, examination of the samples collected indicated ranges of particle sizes that included appreciable portions of all sizes that would be retained in the alveolar spaces of the lungs. TABLE IV.7.-Particle-size characteristics of 481 samples examined by optical microscopy Number of samples Frequency of occurrence, percent Rangeotgeometricmeans,mioron Range of standard geometric deviations 40 8.31 0.25 and smaller--------------------- 1. 87-4. 49 61 12. 68 0. 26-0. 30-------------------------- 1. 65-3. 93 130 27. 03 0.31-0.35-------------------------- 1.60-4.25 122 25.36 0.36-0.40-------------------------- 1.50-3.59 68 14. 14 0. 41-0. 45---------------------- ---- 1. 52-3. 26 35 7.28 0.46-0.50-------------------------- 1.74-3.33 10 2.08 0.51-0.55-------------------------- 2.19-3.24 7 1. 45 0. 56-0. 60-------------------------- 2. 32-3. 14 5 1.04 0. 61-0. 65------------------ ------- - 2. 36-2. 76 2 .42 0. 66-0. 70--------------- ----- ----- - 2. 51-2. 60 1 .21 0. 71-0. 75-------------------------- 2.82 30 r 20 10 0 < 0.25 0.30 0.35 0.40 0,45 0.50 0.55 0.60 0.65 0.70 0.75 RANGES OF GEOMETRIC MEAN PARTICLE SIZES, micron FIGURE IV.2.-Frequency distribution of geometric mean particle sizes. FREE SILICA CONTENT OF DUST Eighty-two samples of airborne dust, 234 samples of settled dust, and 82 bulk (ore) samples were collected and analyzed for free silica (alpha quartz) content during the study. The samples of airborne dust were collected with a high-volume sampler which was operated by a 110-volt motor and therefore could be used only at locations where a suitable power supply was available. Conse- quently, most of the samples of airborne dust were collected either in mill and crusher buildings on the surface, or at underground locations such as shaft stations and dumping points. These samples were of necessity collected during rather short intervals and may not have been representative of continuing conditions. In some 46 ~ = 47 _

mines it was not possible to collect enough airborne dust for analysis within a reasonable time, even with the high-volume sampler. The samples of settled dust were collected more generally throughout the working areas of all the mines studied, and repre- sented dust generated by the mining operations over extended pe- riods of time. Only the portions of these samples that passed a 325- mesh screen were analyzed for free silica. The bulk samples were, in most instances, composites of ore assay samples and pos- sibly contained inordinate proportions of materials that would not become airborne. Of the samples of airborne dust that were ana- lyzed for free silica content, about half the results were in close agreement (exact or within plus or minus 2 percent) with the analyses of settled dust from the same mines. The results of the analyses of the 234 settled dust samples which were taken in the 67 mines were used to classify the mines in re- spect to free silica and as the bases for determining the threshold limit values applicable at each mine. Table IV.8 shows the number of mines in the various free silica ranges, and the distribution of employment among these groups of mines. TABLE IV.8.-Free silica content of settled dust at 67 mines Ranges of free silica, percent Number of mines---____-__ Percent of mines____ Number of inen_____ Percent of inen_____ o-5 9 13.4 1,972 9.6 5-10 11 16. 4 2, 536 12.4 10-20 16 23 9 4, 606 22.4 20-30 12 17. 9 4, 354 21.3 30-40 10 14.9 6,624 32.3 40-50 5 7.5 201 1.0 Over 50 4 6.0 217 1.0 Total 67 100.0 *20, 510 100,0 'More than 60 percent of nationwide empbyment at underground metal mines in underground and surface operations at time of study. Figure IV.3 indicates the percentage of the midget impinger sam- ples in the various free silica ranges. DUST CONCENTRATIONS During the study 789 full-shift weighted average exposures in un- derground operations were determined, involving collection of 14,480 midget impinger samples. These determinations were based upon full-shift sampling of the environment of individual workmen engaged in various mining operations, taking into account the dif- ferent activities involved in each such operation, and time-weight- ing each activity in respect to the overall operation. The full-shift 48 ~ 25 a 20 ~ W a_ 15 Q Cn z 10 ~ 0 0: O 5 M W . 0 z 0 ~ 25 r _ U N 20 vi w 15 a g Q N 0 w U Q h .. rr 5 ~ ~ 0 M --V777777 0-5 5-10 10-20 20-3o an-an an_an rn,o. ~~ 0-5 5-10 10-20 20-30 30-40 40-50 FREE SILICA RANGE, percent Over 50 FIGURE IV.3.-Percentage distribution of midget impinger samples by range of free silica content. sampling provided a representative evaluation of dust exposures re- lated to specific operations, but it is emphasized that results pf the full-shift determinations apply only to operations, as such,-and are not meant to classify the total underground mining' population into various degrees of dust exposure. It may not be assumed that dis- tribution of men among the various operations has been or will con- tinue to remain constant throughout the industry. Moreover, eval- uations on the full-shift basis represented conditions existing only at the time of sampling and may not be considered indicative of past or future conditions.= Figure IV.4- shows the 789 weighted average exposures in the 67 mines studied, plotted to indicate weighted average dust concentra- tion and free silica content in relation to both the threshold limit values in effect in 1958-61, when the study was conducted, and those adopted by the American Conference of Governmental Industrial Hygienists in 1962. Based upon the 1958-61 threshold limits, 44, or 5.6 percent, of the weighted average' exposures exceeded the lim- 49 ON"

UNDERGROUND-GENERAL Although the average concentration of dust in all samples collected at an underground mine has little or no bearing on the exposure of an individual miner, this "mine average" may be useful as a measure of the effectiveness of dust control. Figure IV.5 shows the averages of all midget impinger samples collected underground at each mine in respect to dust concentration '0 ~ and free silica content. ~ o" Figure IV.6 shows the distribution of all midget impinger samples collected underground in respect to dust concentration and free silica content. No marked differences were evident in the distribution of airborne dust concentrations in the mines in the different free silica ranges. This indicates, in general, that the same degree of attention was being given to dust control in low silica mines as in high silica mines. UNDERGROUND OPERATIONS The type of mining method employed usually has an important effect on production of dust, and therefore has a bearing on dust control procedures required. Selective mining usually requires smaller equipment and results in a lower tonnage per employee than full scale mining, such as in block caving. Table IV.10 is a summary of underground occupations for which 8-hour weighted average exposures were calculated. This summary included miners in stopes, raises, and drifts. Transportation em- ployees included haulage crews, diesel truck drivers, shuttle car op- erators, and hand trammers. Maintenance and construction employ- ees included concrete crews, gunite crews, and motor grader operators. Other employees included were exploration drillers, rock bolters, and shaft, station, winze and sump miners. Table IV.15 gives additional data on individual sample groups. Figure IV.7 shows the percentage of midget impinger samples in the various ranges of dust concentration for each principal under- ground operation, as well as for some miscellaneous mining opera- tions not readily classified in respect to mining method. Of the 14,837 results of impinger samples shown in figure IV.6, 1,440 samples, or slightly less than 10 percent, are considered to represent excessive concentrations of dust. Discussion of these 1,440 samples, and conditions contributing to the excessive concentrations, is essential in order that proper recommendations may be made for cor- rection of these conditions. 53 I

0 Each circle.~Epresents one mine 0 O O O 0 0 0 0000000000000 0 0 0 0 0 0 0 0 000 n c0 0 0 00 O 00 O O v 0 0 0 0 0 10 20 30 40 50 60 V 100 FREE SILICA, percent FIGURE IV.S.-®verage of midget impinger samples collected in each mine in respect to dust concentration and free silicaa content. +50 50 m a x ~ ~ 45 ~ a d .t, 40 Y E ~ ~ 30 0 z 0 25 m ~ a 0 20 z 0 a 15 ~ ~ ~.Zi. Z 10 0 U 5 U 10 20 30 40 50 60 r 100 FREE SILICA, percent FIGURE IV.6: Distribntion of midget impinger samples collected in respect to dust concentration and free silicaa content. 111, JIIII 90 34 12 49 2 1 12 14 3 2 2 Total samples, 14,837 Samples containing 23 9 5 10 excessive dust, 1,440 Percent containing excessive dust 9 7 37 16 11 9 1 , . 42 17 4 21 1 1 65 20 17 25 3 1 1 95 65 25 25 3 3 140 111 60 35 9 2 300 190 78 95 20 15 6 660 425 415 240 75 35 3 3,071 2,690 2,320 2,410 410 225 21 JI ~ i, 1 ,' til I, 'jI e', + I r1II' I1I I

TABLE IV.10.-Occupational dust ezposures, underground, weighted averages Occupation Number of places Number of samples Weighted aver- ages mppof Sublevel cave miners_______________ 111 1,746 8.5 Block cave miners__________________ 113 1,725 7.5 Room and pillar miners_____________ 103 1,592 7.1 Shrinkage stope miners _ _ _ _ _ _ _ _ _ ___ _ 15 227 5.4 Open stope miners__________________ 42 651 4.4 Square set miners__________________ 138 2,102 3.3 Cut and fill miners_________________ 87 1,322 312 Top slice miners___________________ :_ 6 97 2.8 Transportation_____________________ 123 1,767 5.2 Maintenance and construction _ _ _ _ _ _ _ 20 305 13.8 Other----------------------------- 31 392 4.0 Man Trips.-Four percent of the midget impinger samples col- lected during operation of man trips contained excessive concentra- tions of dust. These high concentrations were caused by recircula- tion of air, dusty equipment, and dry roadways. Slushing.-Eighteen percent of all samples collected during slush- ing operations contained excessive concentrations of dust. This was due principally to inadequate ventilation, recirculation of air, and lack of sufficient water before and during slushing operations. This is one of the principal sources of dust in mining, and rigid con- trol methods are essential if the general levels of dust concentra- tions throughout the mine are to be reduced to any appreciable extent. Mucking.-Fourteen percent of all midget impinger samples col- lected during machine and hand mucking contained excessive con- centrations of dust. These high concentrations were usually the result of inadequate ventilation, recirculation of air, lack of sufficient water before and during mucking operations, and excessive use of blowpipes. Timbering.-Only 3 percent of the samples collected during tim- bering contained excessive concentrations of dust, and in most cases contaminated air from other sources was a contributing factor. During removal of old timbers, dislodgment of settled dust sometimes created a problem. I Drilling and Loading Holes.-Approximately 11 percent of the samples collected during these operations contained excessive concen- trations of dust. In addition to improper ventilation, collaring of holes dry, inadequate use of water, and defective equipment were the principal deficiencies noted. One sample, collected while a drill was operated 'dry for 3 minutes, contained 460 mppcf. - Use of blowpipes, coupled with substandard ventilation, created excessive OPERATIONS Timbering, rustle material, cleanup Man trips, lunch Tramming Machine, hand mucking Barring down Between operations Drilling, loading holes Concreting and guniting Loading, dumping cars Slushing, breaking boulders . Total operations Million particles per cubic foot • ® ® 0-5 5-20 ~ 20-50 ® 50+ I I I I I 1 1 I I 1 1 0 20 40 60 80 100 SAMPLES, percent FIGURE IV-7.-Ranges and percentages of dust concentrations underground. 56 1 57

concentrations of dust while blowing out holes, which usually was an operation of short duration performed on the average of once each shift. Tramming.-Nine percent of the samples collected during tram- ming operations contained excessive concentrations of dust. This was due to improper ventilation, including recirculation of air, in- adequate maintenance of roadways, and inadequate maintenance of equipment. Loading and Dumping Cars.-In these operations 15 percent of the samples contained excessive concentrations of dust. Improper ventilation, lack of sufficient water to wet the muck thoroughly, and excessive use of blowpipes, both to free muck in the chutes and to loosen the ore in the cars at the dumping points, were the principal factors involved. Skip Tenders.-Skip tenders were exposed about 19 percent of the time to excessive dust concentrations. These concentrations were due usually to the same factors t~at were influencing the load- ing and dumping operations. In addition, the muck was often much drier, due to increased exposure to the ventilating currents. Between Operations.-Approximately 1,450 of the midget imping- er samples collected underground were taken during waiting peri- ods. Men would be waiting for smoke to clear after blasting, for supplies, repairs to equipment, or in many cases, for another train of empty cars before resuming slushing or mucking operations. Seven percent of these samples contained excessive concentrations of dust. In most instances, the dust was created by other opera- tions and was carried to the men by the ventilating current. Men were inclined to wait near the scene of operations, rather than re- treat to a relatively dust-free area. This was especially noticeable where men were waiting for fumes and dust to clear following a blast. In some cases, where several stopes were ventilated by one continuous current of air, dust from one stope would be carried con- siderable distances to men who were waiting downwind. Eating Lunch.-Approximately 5 percent of the midget impinger samples collected while men were eating lunch contained excessive concentrations of dust. In some instances men ate in or close to the working area and were subjected to residual dust in the air, or to dust being carried in the ventilating current from another source. Men frequently entered heated lunchrooms, and when their damp clothing began to dry, considerable dust would be liberated in the lunchroom in which there was no positive circulation of air. Loose plank flooring in lunchrooms was another source of dust. When this condition was pointed out to one company, the plank floors were replaced with floors consisting of 2 by 4's placed on edge, and spaced about one-half inch apart. These floors were then washed twice daily. Concrete and Gunite Crews.-About 15 percent of the dust concen- trations determined in connection with concreting and guniting op- • erations were excessive. Concentrations in excess of 100 mppcf while concreting and in excess of 500 mppcf while guniting, were ebtained. Handling of dry materials, and such practices as loosen- ing sand and cement by beating on the sides of metal mine cars with hammers, contributed to these high concentrations. Approximately_ 25 percent of the employees engaged in this work wore approved respirators. = : Rock Bolting. About 12 percent of the samples collected during _ rock-bolting operations contained excessive concentrations, and in most cases, these were the result of inadequate ventilation. Water was used throughout all drilling operations for rock bolting. Mobile Equipment Operators.-These operators were exposed to excessive concentrations of dust in 15 percent of the cases. Most _ of this was the result of crawler-mounted equipment slipping on hard bottom, poorly maintained roadw. ays, and inadequate ventilation. = Barring Down.-Seven percent of the samples collected during barring down operations contained high concentrations. Much of - this was due to a buildup of dust due to inadequate ventila- tion. Often the ventilating current was insufficient to remove dust from previous operations, such as blasting, especially_.whe_n.the work- men returned to the area very shortly after blasting. Breaking Boulders.-Fifteen percent of the midget impinger sam- ples collected while breaking boulders contained excessive concen- trations of dust. These boulders were broken usually by one of two . methods: secondary blasting, which required the drilling of short holes, or by use of sledgehammers. Many of these short holes were drilled dry, and excessive concentrations of dust were generated. Boulders being broken with sledges were often coated with dry dust which was dispersed as the boulders were broken. On several occasions, recirculated air from another operation added to the dust load. When excessive dust concentrations were present, improper ven- tilation was often a contributing factor. Lack of sufficient air move- ment would result in a buildup in dust concentrations, even in such locations as lunchrooms. Air that was recirculated from another dust-producing operation often added to the general dust load. Some examples follow: (a) Employees walking along a haulageway were exposed to concentrations of 24 mppcf. This was due to dust from other operations being carried along the haulways by the ventilating current. (b) Men barring down in a raise were exposed to air containing 40 mppcf. There was no perceptible movement of air, and a buildup of dust was evident. (c) During slushing op- erations in a drift in which there was no perceptible movement of 58 1 59

dust. Crushing is inherently a dusty operation, and extreme care is essential to prevent the dust from becoming airborne. Improper maintenance of equipment, resulting in leakage around joints, and poor cleanup practices, were evident in many cases. Lack of dust collecting systems and lack of effective ventilation in the buildings were contributing factors. Assayers in 1l1i77•s.-Assayers, when collecting samples, were fre- quently subjected to the same concentrations of dust as other em- ployees working in the mills and around crusher operations. In many instances, the assay laboratory was located in the mill. Lab- oratory procedures included the pulverizing of ore samples, and high concentrations of dust resulted when exhaust ventilation systems were inadequate or nonexistent. The use of airhose by the assayer when cleaning up equipment also was a contributing factor. The pulverizing operations usually were of short duration, and in 25 per- cent of the cases, the '~ssayer wore a Bureau of Mines approved respirator. Sixteen percent of the midget impinger samples col- lected while assayers were working around mills, and in laborato- ries located in mill buildings, contained excessive concentrations of dust. SHOPS AND OTHER SURFACE LOCATIONS A total of 1,660 midget impinger samples was collected in the shops, hoistrooms, and other surface locations. Of this number, only 6.7 percent contained excessive concentrations of dust: Table IV.12 is a summary of the samples, and figure IV.9 shows the distribution in the various ranges of concentration and free silica content. TABLE IV.12.-Midget impinger samples collected at surface locations Location or operation Number of samples 8amples containing excessive concentrattons of dust Number Percent Totad----------------------- 1,660 112 6.7 Shops------------------------------ 1,032 73 7.1 Toplanders and hoistmen_____-______ 231 0 0 Assay laboratories__________________ 117 22 18. 8 D umpmen------------ ------------- 75 0 0 Bullgangs and pumpers____-________ 62 0 0 Concentrateloaders________________ 50 14 28. 0 Shovel, compressor, crane, and truck operators------------------------ 66 0 0 Concrete plants_____________________ 18 3 16.7 Sand blasters______________________ 9 0 0 I t ,D m~ m~ .0 n $v' ~v e Q - E ~ u ~ ~ N !~- tS~ 'VS O, . 'OS N Oti ..y tn N M R) V N .r N N .r n en N fn N In 00 N O d (y (r1 l0 N ~ m ~ m i[) tn a V' M 1rQ) N N .~-~ + O . to 0 4 na rad saloped uo1lllw '1S(10 3N2108211V 30 NOIltl2llN30N00 8 a 0 62 63 707-193 0-64-6

Slaops.-In the shops, 7 percent of the 1,032 midget impinger sam- ples collected contained high concentrations of dust. Lack of ex- haust ventilation was apparent in many locations. Sweeping up dry materials was another factor. The practice of cleaning off ma- chinery by use of compressed air often contributed to the dustiness of the atmosphere. Assay Laboratories.-Assayers sampled in this category included only those working in laboratories which were not located in the mills. About 19 percent of the samples collected in these labora- tories contained excessive concentrations of dust. Pulverizing of ore for assaying created considerable dust, and the use of airhose to clean up equipment tended to keep the dust suspended for some time. In 25 percent of the cases, the assayer wore a Bureau of Mines approved respirator while operating the pulverizing equipmen•t.h' Concentrate Loaders.-These employees were engaged in loading the concentrates for shipment, either by truck or by rail. The con- centrate was usually dry, and caution was required to prevent dissemination of dust into the atmosphere. Of the 50 midget im- pinger samples collected, 28 percent contained excessive concen- trations of dust. As this usually was a part-time operation, the use of approved respirators might offer at least a partial solution. Concret,e PZants•-Few men were employed in concrete plants. Their function was to premix concrete for underground use. Of the 18 midget impinger samples collected in concrete plants, 3 con- tained excessive concentrations of dust. Oth.er Operations.-A total of 443 midget impinger samples was collected at various surface locations and during various operations. There was some question as to the efficiency of air-supplied helmets during sandblasting operations. Nine samples collected inside the helmets contained very low concentrations of dust. Two hundred and thirty-one midget impinger samples were collected in hoistrooms and around the shaft collars while toplanders were performing their normal duties. None of these samples contained excessive concen- trations of dust. None of the 75 midget impinger samples collected while dumpmen were working on the surface contained excessive concentrations of dust. One hundred and twenty-eight midget impinger samples were col- lected where equipment operators, pumpers, and general laborers were working. None of these samples contained excessive concentrations of dust. Table IV.13 is a summary of occupationall classifications for which arithmetic averages, rather than weighted averages, were calculated, as dust concentrations in operations of this type remained fairly constant over a full shift. $ ~ 0 M .4 .n Co o 0 rio.rcrSo'di o 10 OVD N O N 0 01 00 tD M O YJ .-iOcC'W ~d LV -0, ~ 0 oooMwrow 0 wacooea O~O~OCO~•OD~[i 00 W M Ot- nXO 0 un O go r.o~acnOO, ~-g o~~j d ~co~ ooo~an eooo ~ "44 '4 o"oU.~10mo°o =R 0 to ~ N- t` c0 O O Q~ o M ~ Co er Un 00 ~ rn -n a~ uM 00 rn r ho 'occ 14 O N Nc0 MO~ON M M M ~0 CO+n •G M -_j M ~ M N N !r .-I N CD +-~ M ~ ~ G 00 Oc0 OtOMM.0 N M ~ M n O N 000'W cON 0 0 ~ uN7m 'W Co M-+ -~~-~ M ~ N W M N.+ti N ~ ~ ~ ~ 2 ro d U ' tko ! ' ~ 03 O 0 .U U p+a a °iq LIJ 00Nto c3n: N Q~ t0 1r r +-i00C ., c» a~D ~O 00 O N tOOt- ~ M M O n O ~ ~D opu0» O N 64

N MM ~flO VIO~tDO~MOOO.-ilrhd/ g ~ +-i • • .-i r-i ,..i N G`7 a a s ~ ~M,-IO1rhWe0 W ~M u'JOeD ~ ~~ ~ ° ~ ; ~ Iz ~ q O~ Q~eD lrNdlM.yr-i'~~000,--iN0 ~~ ~ I g C+9 O+-7CV CqCV eMCq +t$tG1:cCCi a ;g •~ 00 ONOM u0 MtDOI- N W c00+-idlu~ N +c»r+N Un oMM I z ! M t0 00 M 00 1~ tD a, 00 M 00 O O ti O 00 I~ g g Oi oGOiCI tiGeGeG t0t.: .-i CV CV c+j i`..y 6y' *-1NN NNNMM a ~ 00 C~ O~M~M V/ ot- oe~ o0Nt0 NO~ W Cq cD1~tD oo.-i N cOU7 o~ilrh ,i z N I q ~O NM~O O~cD1~ u0 L~Mr+uJONMH Lr oair`eccp oioSoiodi`ci..:ai~ oSec o> 00 a0 00 00 1' L ir h A. 1- t~. t0 CO M u~ ~ N m N O N CO L` dI tD ,--i O N m~J o'.T ~n o ° ' ° ° `~ M + , -1 oo n . = m nwLO ~VoaCO~a. _ ~ z 'e~ w O 00 T 00 0~ N O eD OD N 1r eD O~ dIMW OOO~cOeHMMM tDt-i~1t~.N+-1 '~ °' dl ,~ M M c0 O~ cO tD 00 u~ M N 'W M N t~ ~ 1 1 1 1 1 1 1 1 1 1 1 I I 1 1 1 1 1 1 ~ 1 I I 1 1 ~ I 1 I 1 ~ 1 ~ 1 1 1 1 1 1 1 1 1 1 I ~ 1 I 1 ~ 1 1 1 1 1 ~ 1 1 1 1 1 ~ 1 ~ ~ i ~ 1 1 1 1 1 ~ ~ 1 1 I 1 ~ 1 ~ 1 1 1 1 I 1 1 ~ 1 1 1 1 1 1 I 1 ~ 1 1 1 1 ~ 1 1 ~ 11 ~ 1 1 I ~ 1 ~ 1 1 I 1 I 1 1 ~ 1 1 ~ 1 1 1 1 ~ i ~ ~ 1 1 1 1 1 ~ 1 1 1 I 1 1 i 1 1 ~ 1 1 1 I 1 1 1 1 I 1 I ~ 1 ~ i ~ ~ 1 ~ 1 1 1 1 1 ~ 1 ~ 1 1 1 1 i ~ 1 ~ ~ t I 1 1 1 I 1 ~ 1 1 1 1 1 1 1 ~ 1 1 1 1 1 i 1 1 1 1 ~ ijg 1 1 1 1 ~ 1 1 I I 1 1 "• ~ 1 1 1 1 1 1 I 1 1 1 1 I O ~ i~ 1 1 1 I 1 1 I t I y / I I 1 1 1 1 1 I 1 I I 1 I I 1 Oj to I I 1 1 I 1 ° ~y'~I~ ' ~~p!y l 1 1 W 1 1 1 ; 6~ a^~q ~ ~ 1 ~ ^ '' I C 1 t 1 (~ Q 0 U I~~ ~p I 1 ~ o U RJ ~ i d4 U o v ,17 'N bD d i W 1 1 Q~ tw m q OA GD q 60 p tD o FsxU~/- 7Eixi~~'2 AA Aa4aim Table IV.14 is a summary of all midget impinger samples used to determine full shift weighted average exposures of underground em- ployees performing various operations. The total number of midget impinger samples listed in this table exceeds the number actually col- lected for this purpose by approximately 10 percent, as numerous samples were used to determine exposures during two or more opera- tions. For example, during the period in which a sample was collected, a haulage crew might load, tram, and dump cars. This sample would be used to indicate exposures during each operation, and thus would be recorded three times in table IV.14. The number of places sampled, number of samples taken, and the high sample and average dust, concentrations are shown in groupings as to locations both surface and underground in table IV.15. In all locations, the lowest concentration sampled contained less than 1 million particles of dust per cubic foot of air. - TABLE IV.15.-Occupational dust exposures, surface and underground Locations Number of places Number of samples High sample (mppc0 Average (mppc) SURFACE Shops: Machinist-mechanic _ _ _ _ _ _ 74 269 20 2 Blacksmith_______________ 42 176 50 3 Welder------------------- 43 152 390 18 Bitsharpener_____________ 14 60 130 7 Drill doctor_______________ 16 57 10 2 Electrician________________ 34 108 20 2 Carpenter________________ 35 127 25 1 Sandblaster_______________ 3 9 4 2 Concrete batch plant oper- ator------------------- 6 18 40 10 Sweeper------------------ 3 6 30 5 Garage------------------- 15 50 5 1 Tinsmith_________________ 6 17 6 2 Saw filer__________________i 6 16 5 1 Surface mine service: Toplander____________ 22 65 3 1 Hoistman-________________ 54 166 3 1 Power shovel operator______ 3 10 2 1 Truck driver______________ 3 10 6 3 Crane operator____________ 5 20 60 5 Compressor operator _ _ _ _ _ _ _ 9 26 5 1 Crusher (surface and under- ground): Dumpman________________ 20 75 26 3 Primary crusher operator_ _ _ 48 175 60 9 Secondary crusher operator__ 21 75 110 10 Conveyor belt operator_-___ 57 192 530 11 Woodpicker_______________ 15 52 55 6 66 i 67

TABLE IV.15. Occupational dust exposures, surface and underground-Continued TABLE IV.15.-Occupational dust exposures, surface and underground-Continued Locations Number of places Number of samples High sam~ple (mppcf) A verage (mPPcQ Locations Number of places Number Of samples High sample (mPPcO Average (mppet) BURFACE-Continued U NDE ROROU ND-continued Crusher (surface and under- ground)-Continued Open stopes:* Stope miner_______________ 16 244 45 3 Fine ore storage___________ 38 122 70 6 Drift miner_______________ 3 42 20 3 Shaker screen or grizzly Raise miner_______________ 2 28 130 10 operator________________ 24 79 45 8 Driller-------------------- 14 225 40 4 Sweeper or cleanup man_ _ _ _ 3 13 270 30 Tracklessloader operator___ 5 79 12 3 Mill (surface and underground): Grinding_________________ 47 179 13 2 Draw-point mucker oper- ator-------------------- 2 33 370 17 Flotation operator_________ 32 117 12 2 Room-and-pillar stopes * Shaker table operator______ 10 38 8 2 Stope miner_______________ 25 393 145 3 Thickener and filter oper- Drift miner_______________ 8 129 170 8 ator-------------------- 17 65 125 4 Stope driller-_____________ ------------ 40 602 520 8 Kiln operator_____________ 11 36 15 2 Traoperator___ 15 236 90 9 Concentrateloader_-_______. 16 50 340 14 Slusher_•___- _____________ 12 182 190 12 Pumpman________________' 13 42 6 2 Powderman-______--_ _ _ _ _ _ 3 50 25 7 Bull gang----------------- 4 12 20 3 Shrinkage stopes:* Reagent mixing_________-_ 14 52 450 25 Stope miner_______________ 11 168 70 6 Assay office_______________ 47 196 120 13 Drift miner_______________ 2 32 40 6 Hoisting (surface and under- Scram drift slusher operator_ 2 27 7 4 ground): Underground hoistman_____ 31 94 40 2 Cut-and-fill stopes:* Stope miner_______________ 50 763 180 3 Skiptender________________ 47 310 100 9 Drift miner_______________ 20 297 90 3 Cager-------------------- 19 76 11 2 Raise miner_______________ 7 106 120 5 Stope filler________________ 10 156 90 3 UNDERGROUND Square set stopes:* Stope miner_______________ 87 1,337 100 3 Haulage and dumps: Drift miner_______________ 22 340 50 3 Conveyor belt operator_ _ _ _ _ 5 43 20 5 Raise minerr___-_-_______ 17 241 40 4 Grizzlyman_______________ 27 140 170 9 Slusher operator________-__ 4 58 40 2 Chute puller______________ 13 106 130 11 Stope filler________________ 8 126 570 10 Dispatcher________________ 6 18 20 4 Block cave stopes:* Mine maintenance: Stope miner (chute tapper) _ 56 852 700 8 Bulldozer operator__ _ _ _ _ _ _ _ 3 17 60 14 Undercut miner___________ 5 76 60 4 Timber repairman _ _ _-_ _ _ _ _ 43 385 170 6 Drift miner_______________ 35 538 50 3 Ventilation crew___________ 3 30 12 2 Raise miner_______________ 17 259 370 10 Track crew_______________ 22 101 70 3 Sublevel cave stopes:* Mechanic_________________ 58 224 50 4 Stope miner-_____________ 49 770 175 6 Electrician________________ 13 44 30 4 Drift miner_______________ 29 455 200 6 Drill doctor_______________ 8 24 12 2 Raise miner_______________ 6 101 170 6 Pumpman________________ 13 55 7 1 Longhole driller___________ 6 94 320 30 Nipper------------------- 10 67 11 . 2 Slusher operator___________ 20 311 120 11 Exploration : Stope filler________________ 1 15 20 10 Sampler------------------ 7 29 55 16 Top-slice stopes:* Diamond driller___________ 20 118 25 2 Stope miner____________-___ 6 97 24 3 See footnote at end of table.

TABLE IV.15. Occupational dust exposures, surface and underground-Continued Locations Number of places Number of samples High sample (mppeQ Average (mppcf) U NDE RanoU Nn-contin ued Transportation:* Locomotive crew---------- 102 1, 509 340 5 Truckdriver--------------- 3 66 45 4 Shuttle car operator-------- 15 170 20 5 Hand trammer------------ 3 22 12 3 Maintenance and construction:* Concrete crew------------- 15 229 170 7 Gunite crew--------------- 2 30 670 80 Motor grader operator------ 3 46 16 3 Miscellaneous:* Shaft, station, winze, and sump miner------------- 26 317 55 3 Rock bolter--------------- 5 75 100 9 The averages shown for these occupational groups are weighted averages. All others are arithmetic averages. DUST CONTROL Dust control and dust evaluation programs were in effect at 40 mines. The ventilation, safety, or industrial hygiene departments were usually responsible for these programs. Continuous dust mon- itoring was routine at many of these mines, and a spot-sampling method was used at the remaining mines in this group. These pro- grams permit detection of sources of high dust concentrations and institution of proper control measures. Most of the usual dust con- trol measures, such as application of water, adequate ventilation, and use of dust collecting devices, were well known to the industry. In most cases, when substandard conditions were found by person- nel conducting this study, they had resulted from failure to recog- nize or apply these well known principles. Table IV.16 lists some of the effective measures used to reduce dust exposures. TABLE IV.16. dfeasures to reduce dust exposures Underground: 1. Sufficient primary ventilation. 2. Auxiliary fans and tubing for secondary ventilation. 3. Wet drilling. 4. Wetting down of muck piles, before and during slushing. 5. Air-water blasts. 6. Water sprays at grizzlies, loading, transfer and dumping points, In In- take and return airways, and along haulageways. TABLE IV.16.-Measures to reduce dust exposure&-Continued Underground-Continued 7. Wetting down of surface areas around air Intakes. 8. Off-shift or end-of-shift blasting. 9. Hydraulic Slling in preference to dry filling. 10. Location of employee with respect to dust generating operation. Surface : 1. Exhaust fans and hoods. 2. Dust collectors. 3. Water sprays and hoses. -- 4. Enclosed or enclosed and pressurized cabs and booths. 5. Filtered air systems. 6. Supplied-air helmets.* 7. Roof ventilators. TJnderground and surface : - - - 1. Air conditioning. 2. Dust collectors. 3. Good housekeeping practices. 4. Application of calcium chloride or oil on haulageways. 5. Dust respirators.* _ . *Not recommended for long intervals; to be used only when dust control measures are not practical.3° Some of the more common practices that produced high dust con- centrations in working places are listed in table IV.17. TABLE IV.17. Pract-lces that oaused dusty conditdona 1. Failure to make proper use of primary or secondary ventilation. In some cases recirculation of air resulted in blasting fumes and dust generated at one location being carried to employees working downwind. 2. Collaring of holes dry, or drilling with an insufficient volume of water. 3. Use of blowpipe to clean roadways, pockets, and to clear holes drilled for blasting. - 4. Use of airhammer without dust control. 5. Poor housekeeping and cleanup piacticea„ - VENTILATION Ventilation is needed for the comfort and efficiency of mine- workers. Well directed ventilation is desirable in every underground working place to replenish oxygen and to remove or dilute harmful gases and dusts2e 21 To insure proper ventilation in each working place, it is essential that a sufficient volume of air be introduced into the mine, preferably by means of electrically operated fans. The air must be properly circulated so that fresh air is delivered to each working section. Some mechanical means of secondary ven- tilation is then usually necessary to assure that sufficient air of good quality is coursed to the individual working places. -

The total volume of air entering each of 53 mechanically venti- lated mines was measured. Data could not be obtained on five other mechanically ventilated mines because of numerous openings to the surface. Nine mines included in the study relied on natural draft for ventilation. Table IV.18 is a summary of ventilation rates at the 53 mines. TABLE IV.18.-Ventilation rates at 68 mines with mechanical ventilation Ventilation Up to 20,000- 50,000- 100,000- Over rates, cfm 20,000. 50,000 100,000 250,000 250,000 Number of mines. 8 15 11 13 6 Table IV.19 lists methods of ventilation in working places in which midget impinger samples of airborne dust were collected. TABLE IV.19.-Methods of ventilation in underground working places Mining method Number of places In-line flow Fan with or without tubing Com- pressed air• Convection or natural draft su®cient to measure Air velocities insufficient to measure Total------ 588 136 178 21 42 211 Percent of total---- 100 23 30 4 7 36 Topslice--------- 9 0 4 0 0 5 Development_____ 10 4 6 0 0 0 Shrinkage-------- 12 5 2 0 0 5 Open stopes------ 39 5 2 5 8 19 Cut and fill stopes_ 58 14 29 0 2 13 Sublevelcave----- 104 14 33 3 14 40 Block cave------- 116 23 27 9 7 50 Room and pillar-_ 56 9 17 0 6 24 Squareset------- 184 62 58 4 5 55 •Air operated fans, and compressed air used only for ventilation. Does not include exhaust air frorq drills and other air-operated equipment. COMPOSITION OF MINE ATMOSPHERES Samples of mine atmosphere were collected at each mine for de- termination of air quality. Such samples were collected only in sit- uations where the quality of the air might be suspect, and did not reflect average conditions in the mine. For example, samples were collected in locations where men returned to the working place Compressed air and water mist spray used during blasting cycle in headings. (Courtesy of_The Anaconda Co., 1963.) shortly after blasting. Samples were collected in all mines where diesel equipment was operating, and in the main returns at each mine. Management was notified in all instances when analyses indicated contaminants in the mine atmosphere in excess of sug- gested limits. Table IV.20 is a summary of all air samples collected under these conditions. Mine air is considered to be of good quality when it contains at least 19.5 percent oxygen, and not more than 0.5 percent carbon di- 73

oxide, 0.01 percent carbon monoxide, or 5 parts per million of nitro- gen dioxide. As field instruments specific for detection of nitrogen dioxide were not available when the study began, the air samples were analyzed for total oxides of nitrogen (except nitrous oxide), for which the suggested limit was 25 parts per million?a As showdin table IV.20, 2 percent of the air samples collected con- tained carbon dioxide in excess of the suggested limit, 5 percent ex- ceeded the suggested limit for carbon monoxide, and 4 percent exceeded the suggested limit for oxides of nitrogen. All samples col- lected contained at least 20 percent oxygen. TABLE IV.20.-Composi.tion of mine atmospheres Constituent Range of concentration Number of samples Percent of total Cumulative percent Percent by volume Carbon dioxide__ Total________________ 307 0.03-0.10--------- 153 50 50 0.11-0.20--------- 91 30 80 0.21-0.30 -------- 28 9 89 0.31-0.40--------- 23 7 96 0.41-0.50--------- 6 2 98 Over 0.50--------- 6 2 100 Percent by volume Carbon monox- Total________________ 300 ide . None detectable__- 203 68 68 Less than 0.0025 __ 21 7 75 Not over 0.005---- 26 9 84 0.005-0.01-------- 33 11 95 Over 0.01--------- 17 5 100 Parts per million Oxides of nitro- Total________________ 276 gen * . 0---------------- 158 57 57 0-5 -------------- 39 14 71 6-10------------- 36 13 84 11-15------------ 19 7 91 16-20------------ 9 3 94 21-25------------ 5 2 96 Over 25---------- 10 4 100 Percent by volume Oxygen--------- None under 20. •Total oxides of nitrogen, except nitrous oxide, NsO. Portable instruments specific for determination of nitrogen dioxide not available for field use at time of study. 0 U z d b o p 0 0 74 1 75

CONCLUSIONS ON DUST PRODUCTION AND CONTROL The foregoing discussion of observed conditions in underground and surface operations leads to the following conclusions : 1. The effective use of the ventilating currents in the working areas was indicated as a problem which needed immediate attention. 2. Water applied to the muck piles will assist materially in re- ducing dust concentrations during subsequent operations. 3. Drilling, slushing, and crusher operations were the most prolific dust-producing operations to which men were directly exposed. 4. Dust concentrations in shops, except during cleanup opera- tions, presented no particular problems. 5. Better maintenance, cleanup procedures, and dust control measures were indicated around crusher installations and concentrate loading. 6. It was noted, incidentally, that ventilation often was inade- quate during welding operations. REFERENCES 1. Jackson, C. F., and J. H. Hedges. Metal Mining Practice. Bureau of Mines Bull. 419, Vpashington : U.S. Government Printing Office, 1939. (Out of print. ) 2. Jackson, C. F., and E. D. Gardner. Stoping Methods and Costs. Bureau of Mines Bull. 390, Washington : U.S. Government Printing Office, 1936. (Out of print. ) 3. Peele, Robert. Mining Engineer's Handbook. New York: John Wiley and Sons, Inc., 1952. Sec.10 : 1-640. 4. Bucky, P. B. Mining by Block Caving. Wilmington, Del.: Hercules Powder Co., 104 pp., 1945. 5. Brown, Carlton E., and H. H. Schrenk. A Technique for Use of the Im- pinger Method. Bureau of Mines Information Circular 7026,1938. 6. Schrenk, H. H., and Florence L. Feicht. Bureau of Mines Midget Im- pinger. Bureau of Mines Information Circular 7076, 1939. (Out of print.) 7. Brown, Carlton E. Midget Microprojector for Dust Determinations. Bureau of Mines Report of Investigation 3780, 1944. 8. Anderson, F. G. A Technique for Counting and Sizing Dust Samples with the Microprojeetor, American Industrial Hygiene Association Journal 23: 330-336, July-August 1962. 9. Ballard, James W., H. I. Oshry, and H. H. Schrenk. Quantitative Analysis by X-ra.y Diffraction. I. Determination of Quartz. Bureau of Mines Re port of Investigation 3785,1944. ( Out of print. ) 10. American Society for Testing Materials. Committee E-E, Methods for Emission Spectrochemicai Analysis. Philadeiphia : American Society for Testing Materials, 685 pp. 1960. 11. Bureau of Mines. Sampling and Analysis of Mine Atmospheres. Bu- reau of Mines Miners' Circular 34, 1948 rev. 12. Berger, L. B., and H. H. Schrenk. Bureau of Mines Haldane Gas-Anal- ysis Apparatus. Bureau of Mines Information Circular 7017, 1938. 13. Polis, B. D., L. B. Berger, and H. H. Schrenk. Colorimetric Determina- tions of Low Concentrations of Carbon Monoxide by Use of a Palladi- um Chloride-Phosphomolybdic Acid-Acetone Reagent. Bureau of Mines Report of Investigation 3785,1944. ( Out of print. ) 14. Beatty, Robert L., L. B. Berger, and H. H. Schrenk. Determination of the Oxides of Nitrogen by the Phenoidisulfonic Acid Method. Bureau of Mines Report of Investigation 3687, 1943. 15. American Medical Association. The Development of Threshold Limit Values, A.M.A. 9.rchives of Industrial Health 12: 685-687, December 1955. . . . ; _ 16. Proceedings of the Eighth Annual Meeting of the American. Conference of Governmental Industrial Hygienists, Chicago, Ill., Apr. 7-13, 1946. 17. American Conference of Governmental Industrial Hygienists. Thresh- old Limit Values for 1958, Archives of Environmental Health 18: 178-182, August 1958. 18. American Conference of Governmental Industrial Hygienists. Thresh- old Limit Values for 1962, American Industrial Hygiene Association Journal 23 : 419-i23,1962. 19. Pearce, S. J. Use and Abuse of Reaparatory Protective Devices. Trans. National Safety Council, Industrial Safety Section, 1952. pp. 32-37. - 20. Bureau of Mines. Fires, Gases, and Ventilation in Metal and Nonmetal- lic Mines. Bureau of Mines Miners' Circular 55, 1955 rev. 21. McElroy, G. E. Engineering Factors in the Ventilation of Metal Mines. Bureau of Mines Bull. 385, Washington: U.S. Government Printing Office, 1935. 22. American Standards Association. American Standard Allowable Concen- tration of Omides of Nitrogen. Jan. 19, 1944. Part B-History of Dust Sampling and Comparison_of Methods : Since the development in 1886 of the sugar tube for the collection of airborne bacteria and its subsequent application in the collection of airborne dust, various methods for the evaluation of man's ex- posures in dusty industrial environments have been suggested, and improvements in methods of collection and measurement of par- ticulate matter have been made. During this period several meth- ods of evaluation developed in the United States, Great Britain, Germany, and other parts of the world have gained some measure of acceptance and use. Table IV.21 lists in chronological order some of these major developments. Although research in the United States has continued on other methods of evaluation, since the early 1920's investigators in this country have almost exclusively utilized standard or midget im- pingers for sample collection, and light-field microscopy for counting, in the measurement of exposures to pneumoconiosis-producing min- 76 1 77

v co Bureau of Mtnes APPROXIMATE CHRONOLOGICAL RECORD OF DEVELOPMENT OF SOME OF THE METHODS USED FOR DETERMINING DUST IN AIR Approx- imate dates Before 1870 1986 1888 1902- 1903 1905- 1907 TABLE iV.21: Methods for determination of dust in air U.S. Public Health Service Amount of dust in air usually estimated visually. ------------------------ Otlners Sugar tube used in determining dust in .air of subways of New York City.5 V II IrII I^1'XIIII II B9l,li1ll U011V. I P., II „j I ll p 1I" I'Il ;I II ; England Sugar tube described by Frankland for use in sampling bacteria in air i Aitken described his dust counter later much used for determining par- ticulate matter in ordinary air.z Dust collected from air of Cornish mines by filtration through cotton wool and deter- mined by weighing! ---------------- Sauth Africa Dust collected from air of mines by filtration through sugar tube and determined by weighing! -------------------- IC°1'1li16il!IIIiLiw , ill l' I 4 0111 11111 I I'± 1,14 04

---.- ---« --- 0 TABLE IV.21: Methods for determination of du8t in air-Continued APPROXIMATE CHRONOLOGICAL RECORD OF DEVELOPMENT OF SOME OF THE METHODS USED FOR DETERMINING DUST IN A1R--cOntlnued Approx- imate dates Bureau of Mines U.S. Public Health Service Others England South Africa 1908 ------------------------ ---------------------- Use ofthe method -------------------- -------------------- for counting orga- nisms in water for counting dust in the liquid from sugar- tube samples de- scribed." 1909 ------------------------ ---------------------- The American Public -------------------- -------------------- Health Association recommended use of sugar tube for collecting samples of dust from air "heavily laden with dust" and deter- mination of collected dust by weight or count of number of particles.7 1911 ------------------------ ---------------------- Use of paper thimble -------------------- Extensive use of for collecting dust sugar tube method from blast-furnace for determining - - - gas described.8 dust in air of mines began. Dust weiRhed! 1912 1913 1914 1915 1916 1917 --------------- Determined dust in air of mines of the Joplin District by collecting dust, from air by sugar tube and weighing collected dust.10 ------------=-----------I ---------------------- Method for determin- ing dust in air by causing dust to im- pinge against an ad- hesive surface in a Petri dish and count- ing dust described by Graham Rogers. This method accepted by American Public Health Association? ---------------------- Palmer apparatus de- scribed. Dust to be weighed or counted." Palmer apparatus method recommended by American Public Health Association. Dust to be counted.tg Sugar tube adopted by Miners' Phthisis Prevention Com- mittee.4 Largest dust particles in ash of silicotic " lungs were found to be about 12 microns in diam- eter.4 Liquid suspension from sugar-tube samples filtered through 300-mesh ' screen to remove large particles.4 Kotze konimeter de- sern'bed. Dust count- ed.4 -------------------- dh ' b fll IIUG~r

TABLE IV.21. Methods for determination of dust in air-Continued APPROXIMATE CHRONOLOGICAL RECORD OF DEVELOPMENT OF SOME OF THE METHODS USED FOB DETERMINING DUST IN dIH-continued Bureau of Mines Method of counting and weighing dust above and below 10 microns in sugar-tube samples described.1b U.S. Public Health Service Palmer apparavus used in studies in potteries. Dust counted and weighed.f4 ---------------------- Others Small electric precipita- tor described by Bill.ia Comparative study of the sugar tube, Palmer apparatus, Kotze konimeter, paper thimble, and Anderson-Armspach dust determinator was made at the Bureau of Mines, Pittsburgh Station, by the Bureau of Mines, Bureau of Chemistry, American Society of Heating and Ventilating Engi- neers' Research Laboratory, and the Public Health Service 17 Green- burg-Smith impinger was developed during this study and included in the later part of the study.19 Siliceous dust in water over 24 hours found to be somewhat solu- ble. Use of alcohol instead of water sug- gested for such dusts?0 South Africa Acid vapor treat- ment of konimeter, slides started. Dark-field counts of konimeter sam- ples started.'j Flugge-de-Smidt- Zeiss konimeter described.2' The practice of separat- ing dust into -F 10 micron fractions and of weighing dust in impinger samples- discontinued.u ------------------------ Midget impinger de- scribed.29 Microprojection method for counting dust in impinger samples de- scribed.ao ------------------------ Impinger method used in studies of health of workers in dusty trades. Dust count- ed and weighed. Cells allowed to settle 30 minutes. Konimeter also used in low-dust concen- trations?I Impinger method as used by Public Health Service de- scribed.25 ---------------------- ---------------------- ---------------------- Alternating-current precipitator de- scribed." Modified form of the Greenburg-Smith impinger described by Hatch et al?a Hatch cell described.28 Barnes-Penney elec- trostatic precipitator described?I -Prepared sedimentation specimens for use with electron micro- scope (German)?2 Dust-counting meth- ods in which cells 0.1 mm. deep used described u 3+ II 1' 'I bl ;.tl f° II1'Ip England Owens jet dust counter described. Dust counted.1® Thermal precipita- tor described.27 II d i I 1 11 ,,; I11I1,i~

V bi) , w W ~~ f.G. ~ U 1 a o O~•N 0 b~ A ' ~ A , 8 V A , I 1 , , . , , i p a~ ti b ffi ~ 1 1 o V ~ U O ; w .21 a a R V {~ cd ~ao~c 1 1 °~.~~a w eq eral dust. Threshold limit values used in this country for interpret- ing the hygienic significance of exposures to such dusts are based upon these techniques. As a consequence it is necessary, in studies of dust exposures, to obtain data by these methods to permit com- parison with past experience and with the accepted standards. Although the impinger sampling, light-field counting method as applied in the United States has in the past, and continues now, to serve well as a general index of exposure upon which dust control may be designed or assessed, it does not define all of the factors believed to be of physiological importance in exposures to pneumo- coniosis producing dusts. No other method, or combination of meth- ods, however, has been shown to define the long sought dust exposure-physiologic response relationship; nor is there complete agreement among investigators regarding the measurable parameters which will define this relationship. Knowledge regarding the ex- posure-response relationship can be furthered, however, by con- tinued study and application of a variety of environmental assessment techniques both in the laboratory and the field. Throughout the course of the 1958-61 dust exposure study the standard methods of impinger dust sampling and light-field micro- scopic counting were applied for the determination of atmospheric dust concentrations. Cellulose ester membrane filters were used for the collection of atmospheric dust samples for the determina- tion of particle-size distributions by optical and electron micros- copy. Dust samples obtained underground for free silica analysis were, for the most part, settled dust samples, although a limited number of high volume filter• and electrostatic precipitator samples were obtained in mines where electric power was available in suit- able locations for operation of the sampling equipment. At surface operations settled dust samples, and high volume filter and electro- static precipitator samples of airborne dust, were obtained for free silica analysis. Free silica analyses were performed on the portions of settled dust which passed a 325-mesh screen. The application of special sampling techniques in the routine dust exposure study was limited. Special studies were, however, con- ducted in' laboratories of the Public Health Service and the Bureau of Mines, and in selected mines, to compare the results obtained with several additional dust sampling and quantitation techniques to those obtained by the standard methods used in the routine sur- veys. These were comparative studies and were not directed to determining occupational exposures per se. Comparative data were obtained for the following situations or combinations of sampling or quantitation techniques : 1. Standard light field and phase contrast microscopic counts of midget impinger samples. 87 ., i

2. Various combinations of simultaneous or companion sam- ples with midget impingers, cellulose ester membrane fil- ters, thermal precipitators, and a light scattering aerosol photometer in mines and laboratories for particle count and size distribution. 3. Settled dust and companion airborne dust samples for free silica analyses of various fractions separated according to particle size. Eighty-four midget impinger samples obtained at various min- ing operations were counted both by the standard light-field micro- projector method as used throughout the dust exposure study and by phase contrast microscopy using a 16-mm. (10 power) 0.25-N.A. objective. Since dust particles are detected in light-field mi- croscopic observation by their interference images and in phase contrast microscopy by images resulting from phase shift between diffracted and. undiffracted light, which enhances contrast for cer- tain particles, a difference in concentration resulting from counts of the same sample by the two methods may be expected. Never- theless, the data show a strong relationship between the two meth- ods; the phase contrast count was ordinarily about 1.2 times higher than the companion light field count. Dust concentrations as determined by light-field and phase con- trast counts of midget impinger samples were compared with the concentrations calculated for companion samples obtained by vari- ous other methods. Companion samples were obtained with mem- ;brane filters, thermal precipitators, and a,light scattering aerosol photometer. They were obtained both at mines. under normal work- ing conditions and from a laboratory dust chamber under controlled conditions. The coefficients of correlation and ratios of dust con- centrations yielded by midget impinger sampling and companion samples by these other methods are shown in table IV.22. In general, the correlation between impinger results and results by other methods ranged from nominal to, good . for. individual field or laboratory situations in which factors such as particle-size dis- tributions and states of agglomeration would be expected to be rea- sonably constant. ' Combinations of data representing a variety of situations in which factors such as size distributions and states of agglomeration could be different resulted generally in lower values for the coefficient of correlation. Even in cases of good correlation between results by two different methods, the ratio of concentra- tions determined by the two methods might differ substantially from unity. This is to be expected since the methods used may• involve such differences as observation of different portions of size distri- bution curves or the results by the methods being compared may be affected differently by the state of agglomeration of the airborne sample. oQ U$ a ~ ~ . ~ ~ ~ 0 a`3 ~ ~ .~ ~ .~ b ~ . W a ~ H ~ o ~ ~ ~ w ~ ~ c°Oi ,~- .4 .- .4 N c3 .-i .- . ~ ~ ~ M - ti ~ ~ ~. ~ ~ o . . . . . . ~ ~. c°~, ~O :° ~- 00 ~- = . ~ a a a a ~ 0 VJ U Got ~ M Fo F Fp Fp Fo ...•••flffp~ ~> Ca V GI V V t,J V V Cl a d d a~ a~ ~ od $ doa O " .a .a 0 0 c~ o~ o w a a a, a ~~ •~ ~'" "b F7 U O 'FU~ U CFJ .~I O.oo ~~ ~ ~~ ~ ~ *' ~ i' •~ ~ 4 > "' - +a ~ ~ ~ . ~ ~ F f° ~ > ~> 'sa,Z ~ n° o ~° ~~.~~ ~ i.~ Fl F ~ Fo ~ ~ q v~ ~ ~ F a~a3aa°p °~°q aan~o~"NaFaoa~ a3 W ~ O al A aJ o~ O "^' ~ ° a~ ~4) w a~i E'7 a~i ~0 0 a~i ~EQI) E~ a~i m' o N N F ~,. G. ~ y _ y a a a o ~ o C b O+' ~ q o P. O ° •R U~+ t~ ao w O'O v J FQ 8' V ~ U,p (/~ F +~ Fo~ Fp N FO V Fp'~ Fe V pp N 2 o ~ o~o'o~'ov;amR F ~ o aoiao aQ'a,o F 0 ~2 °~."~.~~~.2 'L~ fi1 p ul ro y'b F ro y ro F ro'U 'C~ VJ ~a a aw ~w ~w ~w aw tiva a : E 0 ~ ~ cd ~ m,~ Qa x cd m cd ~C A 4 .q x 4 ~ .ti .~ cd ~ cd 00 W~y w•00 V C~1CJ 210 t~ bA C~ bo F_h9 w a" a a" a a a" "M3ia 88 1 89

TABLE IV.22.-Comparison of dust concentrations from midget impinger samples with concentrations from companion samples by other methods-Continued Midget impinger samples Light-field microprojector count, labora- tory chamber samples, molybdenum ore dust. Light-field microprojector count, all labo- ratory chamber samples. Light-field microprojector count, surface operation samples. Light-field microprojector count, mine samples. Phase contrast microscope count, mine samples. Light-field microprojector count, labora- tory chamber samples, silica dust. Light-field microprojector count, labora- tory chamber samples,lead-zinc ore dust. Light-field microprojector count, labora- tory chamber samples, mercury ore dust. Companion samples Number of pairs of samples Ccefficient of oorrelation' Ratio-mean companion sample concentration; mean midget impinger concentration Thermal precipitator, light-field m~cro- 20 0.72 1.93 projector count, 16 mm. objective. t Thermal precipitator, light~eld micro- 76 .59 projector count, 16 mm. objective. Thermal precipitator, light-field micro- 5 .95 1.54 projector count, 16 mm. objective. Thermal precipitator, phase contrast mi- 6 .86 3.7 croscope count only ef particles more than 0.8 micron, 4 mm. objective. Thermal precipitator phase contrast mi- 6 .98 3.3 croscope count only cf particles more than 0.8 micron, 4 mm. objective. Thermal precipitator, light-field micro- 20 .91 6.7 projector count, 2 mm. oil immersion objective. Thermal precipitator, light-field micro- 16 .85 2.7 projector count, 2 mm. oil immersion objective. Thermal precipitator, light-field micro- 20 .93 3.1 projector count, 2 mm. oil immersion objective. Light-field microprojector count,laboratory Thermal precipitator, light-field micro- 20 .97 5.3 chamber samples, molybdenum ore dust. Light-field microprojector count, all labo- projector count, 2 mm. oil immersion objective. Thermal precipitator, light-field micropro- 76 .69 ratory chamber samples. Light-field microprojector count, mine sam- jector count, 2 mm. oil immersion ob- jective. Thermal precipitator, phase contrast 6 .84 39.0 ples. Light-field microprojector count, surface microscope counts, 1.8 mm. oil immer- sion objective. Thermal precipitator, phase contrast mi- 4 .98 5.0 operation samples. Light-field microprojector count, routine croscope counts, 1.8 mm. oil immersion objective. Thermal precipitator, light-field micro- 25 .36 9.7 mines survey samples. Light-field microprojector count, mine sam- projector counts, 1.8 mm. oil immer- sion objective. Aerosol photometer count, particles more 21 .89 .97 ples. Phase contrast microprojector count, mine than 0.8 micron. Aerosol photometer count, particles more 22 .71 .70 samples. than 0.8 micron. *r= nEXY-EXEY -~[nEXa- ( EX )'] [nBYs- ( EY )']

As stated earlier, free silica determinations have customarily been made on those portions of settled dµst samples which pass through a 325-mesh screen. Because airborne particles of different particle sizes do not penetrate and are not retained in the alveoli and noncilliated lung passages in equal proportions, the free silica content of dust in various size ranges is of interest. Relatively few dust particles of the density of quartz and of size greater than about 4.5 microns equiva- lent diameter penetrate and are retained in the alveolar spaces. Settled dust samples obtained from various locations in mines and at surface operations were screened through a 325-mesh screen. A portion of each screened sample was air elutriated to obtain a frac- tion containing only the particles less than 5 microns in diameter. Chemical analysis of these smaller than 5 micron fractions invari- ably yielded lower free silica contents than did analysis of the unelu- triated portion ,of the samples wIiich passed the 325-mesh screen. In the 56 samples from 271ocations examined in this manner the free silica content of the smaller than 5 microns fraction averaged 48 percent of that of the smaller than 325 mesh fraction. The analytic results for free and total silica content of the samples from these locations are shown in table IV.23. TABLE IV.23.-Settled dust samples: free and total silica content of screened fracti-ns and free silica content of air elutriated fractions Percent free silica Percent total silica Location -326meshfraction Less than b -326 mesh fraction micron fraction 1--------------------------- 63 35 71 2--------------------------- 52 28 58 3--------------------------- 34 21 40 4--------------------------- 31 17 32 b--------------------------- 29 9 46 6--------------------------- 27 18 28 7--------------------------- 27 9 36 8--------------------------- 26 9 43 9--------------------------- 24 11 47 10-------------------------- 24 10 44 11-------------------------- 21 13 40 12-------------------------- 21 6 49 13-------------------------- 19 14 32 14-------------------------- 19 12 26 15-------------------------- 18 7 31 16-------------------------- 17 14 43 17-------------------------- 14 6 27 18-------------------------- 13 8 15 19-------- ----- ----- - 13 5 23 20-------------------------- 12 4 23 21-------------------------- 10 1 21 22-------------------------- 7 2 15 23-27----------------------- Lessthan 1___ Less than 1_-_ 4-21 I t It is recognized that size classification will occur as particles set- tle out from the air, so settled material does not necessarily repre- sent airborne material either in size distribution or composition. Although the data obtained on these settled dust samples are strong evidence that the free silica content of respirable dust is unlikely to be the same as that of settled dust, they do indicate that some de- finable relationship between the two may exist. Samples of the respirable fraction of airborne dust, as such, were not obtained. Electrostatic precipitator samples of total airborne dust were, how- ever, obtained in nine underground working places from which settled dust was taken. The average percent free silica for these samples for each location was usually near that of the less than 5 microns fraction of the companion settled dust samples. The air- borne dust samples averaged 53 percent of the free silica content of the smaller than 325 mesh fractions of the settled dust while the less than 5 micron fractions averaged 54 percent. Data for these samples are.shown in table IV.24. It should be pointed out that the composition of either settled dust or airborne dust is expected to vary from one location to another in a mine, and that airborne dust is expected to vary more in composition than is settled dust. TABLE M24.-Compartison of free silica content of screened and air elutriated fractions of settled dust with that of companion electrostatic precipitator ramples of airborne dust. Percent free silica . Location A-------------------------- B-------------------------- c-------------------------- D-------------------------- E-------------------------- F ----------r -------------- G-------------------------- H-------------------------- I--------------------------- Bettled dust samples (18 samples) Electrostatio pr l p ee ator -325 mesh fraction Less than 5 micron fraction s 1 Pl ~ (27 samples) 63 35 10 52 28 23 34 21 17 31 17 18 29 9 14 27 18 16 26 9 10 21 13 14 19 12 18 Data from the supplemental studies, which have been summarized here, are of no value at this time for assessing the severity of expo- sure for interpretation by current standards. They may, however, be of value for reference by investigators in the future who may use instruments similar to those which have been used and may wish some indication of the relationships between these methods, as 92 93

applied at this time, and the midget impinger light-field counting method as used in the present study. REFERENCES 1. Frankland, P. F. A New Method for the Quantitative Estimation of the Microorganisms Present in the Atmosphere. London : Phil. Trans. Roy. Soc. 178: 113-152, Dec. 9, 1886. 2. Aitken, J. Trans. Roy. Soc., Edin., Vol. 35, 1888. (In Gibbs, W. E. Clouds and Smokes. Philadelphia : P. Blakiston's Son & Co., 1924. 240 pp. See pp. 113-115 and 128.) 3. Haldane, J. S., J. S. Martin, and R. A. Thomas. Health of Cornish Miners. Report to the Secretary of State for the Home Department. London: H. b1'. Stationery Office, 1904. 4. Union of South Africa. The Prevention of Silicosis on the Mines of the Witwatersrand. Pretoria, South Africa : Government Printer, 1937. See pp. 273. 5. Soper, G. A. The Air and Ventilation of Subways. New York: John Wiley & Sons, 1908. pp. 244. 6. Winslow, C. E. A. A Method for Determining the Number of Dust Par- ticles in Air, Engineering News 60 : 748, Dee. 31, 1908. 7. American Public Health Association. Report of the Committee on Stand- ard Methods for the Examination of Air, American Journal of Hygiene 6: 349-351, 1910. 8. Brady, W., and L. A. Tousalin. The Determination of Dust in Blast- Furnace Gas, Journal of Industrial and Engineering Chemistry 3: 662- 670, September 1911. 9. American Public Health Association. Progress Report on the Committee on Standard Methods for the Examination of_ the Air, American Journal of Public Health 3: 78-86, 1913. 10. Lanza, A. J. and E. Higgins. Pulmonary Disease Among Miners in the Joplin District, Missouri, and Its Relation to Rock Dust in the Mines. Bureau of Mines Tech. Paper 105, 1915. 11. Palmer, G. T. A New Sampling Apparatus for the Determination of Aerial Dust, American Journal of Public Health 6: 54-55, 1916. 12. American Public Health Association. Final Report of the Committee on Standard Methods for the Examination of Air, American Journal of Public Health 7: 54-72, 1917. 13. Bureau of Mines records. 14. Newman, B. J., W. J. McConnell, O. M. Spencer, and F. M. Phillips. Lead Poisoning in the Pottery Trades. Public Health Bull. 116, Washington : U.S. Government Printing Office, 1921. (Out of print.) 15. Bill, J. P. The Electrostatic Method of Dust Collection as Applied to the Sanitary Analysis of Air. Journal of Industrial Hygiene 1: 323-342, 1919. 16. Selvig, W. A., F. D. Osgood, and A. C. Fieldner, Collection and Examina- tion of Rock Dust in Mine Air. Bureau of Mines Report of Investigation 2122,1920. (Out of print.) 17. Bureau of Mines • Bureau of Chemistry ; American Society of Heating and Ventilating Engineers, Research Laboratory ; and Public Health Service. Comparative Tests of Instruments for Determining Atmospheric Dusts. Public Health Bull. 144, Washington • U.S. Government Printing Office, 1925. (Out of print. ) 1 i t r I 18. Owens, J. S. Jet Dust-Counting Apparatus, Journal Industrial Hygiene 4 : 522-534, 1923. _ 19. Greenburg, L. and G. W. Smith. A New Instrument for Sampling Aerial Dust. Bureau of Mines Report of Investigation 2392, 1922. (Out of print. ) 20. Meyers, W. M. Solubility of Finely Divided Rock Dusts in Water, Kerosene, and Alcohol. Bureau of Mines Report of Investigation 2548, 1923. 21. Thompson, L. R., D. K. Brundage, A. E. Russell, and J. J. Bloomfield. The Health of Workers in Dusty Trades. I. Health of Workers in a Portland Cement Plant. Public Health Bull. 176, Washington: U.S. Government Printing Office, 1928. See pp. 24-28. ( Out of print. ) 22. Drinker, P., R. D1. Thomson, and S. 11i:. Fitchet. Atmospheric Particu- late Matter. II. The Use of Electric Precipitation for Quantitative Determinations and Microscopy, Journal of Industrial Ilygiene 5: 162-185, 1923-24. 23. Green, H. L. Some Accurate Methods of Determining the Number and Size-Frequency of Particles in Dust, Journal of Industrial Hygiene 16: 29-39, 1934. 24. Lowe, F., Z. Instrumentenkde, Vol. 49, 1929. (In Heymann, B., Methods for the Quantitative Determination of Dust in Air, Zentralblatt flu die gesamte Hygiene 24: 1-38, 1932.) • A 25. Greenburg, L. and J. J. Bloomfield. The Impinger Dust Sampling Ap- paratus as Used by the United States Public Health Service, Public Health Reports 47: 654-75, 1932. 26. Hatch, T., Ii. Warren, and P. Drinker. A Modified Form of the Greenburg-Smith Impinger for Field Use, With a Study of its Operating Characteristics, Journal of Industrial Hygiene 14: 301-311, 1932. 27. Whytlaw-Gray, R. and H. S. Patterson. Smoke. London: Edward Arnold and Co., 1932. pp. 25-41. 28. Hatch, T. and 0. L. Pool. Quantitation of Impinger Samples by Dark Field Microscopy, Journal of Industrial Hygiene 16: 177-191,1934. 29. Littlefield, J. B., F. L. Feicht, and H. H. Schrenk. The Bureau of Mines Midget Impinger for Dust Sampling. Bureau of Mines Report of Inves- tigation 3360, 1937. (Out of print.) - 30. Brown, C. K., L. A. H. Baum, W. P. Yant, and H. H. Schrenk. Micro- projection Method for Counting Impinger Dust Samples. Bureau of Mines Report of Investigation 3373, 1938. (Out of print.) 31. Barnes, E. C. and G. W. Penny. An Electrostatic Dust Weight Sampler, Journal of Industrial Hygiene 20: 259-265, 1938. 32. Friess, H- and H. O. Muller. Die Gasmaske 11: 1-9, 1989. 33. Williams, C. R. and L. Silverman. A Method of Counting Samples Taken With the Impinger, Journal of Industrial Hygiene and Tomicolopy 21: 226- 230,1939: ; 34, Olheiser, H. R. and L. B. Lawrence. Dust Counting-A Simplified Tech- nique, Journal of Industrial Hygiene and Tomicology 22: 472-476, 1940. 35. Bedford, T. and 0. G. Warner. Chronic Pulmonary Disease in South Wales Coal liiners. II. Environmental Studies, B. Physical _ Studies of the Dust Hazard and of the Thermal Environment in Certain Coal Mines. Med. Research Council (Brit.) Spec. Report. Ser. No. 244, 1943. pp. 1-79. 36. Riedel, G. ILolloidzschar. 103: 228-232, 1943. 37. LaMer, V. K. and D. Sinclair. Verification of the Mie Theory-Calcula- tions and Measurements of Light Scattering by Dielectric Spherical Particles. OS RD Report 1857, U.S. Department of Commerce, Report 944, 1943. 94 , 95 707-103'0-64-8

38. Brown, C. E. Midget Microprojector for Dust Determinations. Bureau µ of Mines Report of Investigation 3780, 1944. "39. Brown, C. E. Filter-paper Method for Obtaining Dust-Concentration Re- t sults Comparable to Impinger Results. Bureau of Mines Report of Investigation 3788,1944. (Out of print.) 40. McCartney, J. T. Determination of Size Distribution of Fine Coal' Par- ticies by the Electron Microscope. Bureau of Mines Report of Inves- tigation 3827, 1945. (Out of print. ) 41. 11iay', K. R. The Cascade Impactor, an Instrument for Sampling Coarse Aerosols, Journal of Scientific Instrumenta 22: 187-195, 1945. 42. Silverman, L. and C. R. Williams. An Apparatus for Rapid Sampling of Large Air Volumes for Industrial Air Analysis, Journal of Induatrial Hygiene and Toxicology 28: 21-25, 1946. 43. Gucker, F. T., Jr., H. B. Pickard, and C. T. O'Konsi. A Photoelectric Instrument for Comparing Concentrations of a Very Dilute Aerosol and Measuring Low Light Intensities, Journal of the American Chemical Society 69 : 429-438, 1947. 44. Walton, W. H., R. C. Faust, and W. J. Harris. A Modified Thermal Precipitator for the Quantitative Sampling of Aerosols for the Eleetron Microscope. Porton Tech. Paper No. 1, Ser. 83, 1947. Chemical De- fense Experimental Establishment, England. 45. Walton, W. H. The Application of Electron Microscopy to Particle Size Measurement. Symposium on Particle Size Analysis 1947. pp. 1-13. 46. Hatch, T., and W. C. L. Hemeon. Influence of Particle Size in Dust Exposure, Journal of Industrial Hygiene and Toxicology 30: 172-180, 1948. 47. Clark, H. F., E. E. Geldrick, H. L. Jeter, and P. W. Kabler. The Mem- brane Filter in Sanitary Bacteriology. Public Health Reports 66: 951-977, 1951. 48. Reznik, I. B. Gravi-Micrometric Determination of Dust in Air by Membrane Filter Methods, C#igiena i Sanitariia pp. 28-38, 1951. 49. Fraser, D. A. Absolute Method of Sampling and Measurement of Solid Airborne Particulates. A.M.A. Arck%vea Industrial Hygiene and Occu- pational pational Health 8: 412-419, 1953. 50. Walton, W. H. Theory of Size Classification of Airborne Dust Clouds by Elutriation, Sritiah Journal of Applied Physics, Supplement No. 3, 1954, S29-S39. 51. Dawes, J. G. and B. A. Maguire. Calculation of the Relationship Be- tween Particle Number, Area, and Weight Concentration of Coal Mine Dust Cloud. Safety in Mines Research Establishment, Ministry of Power, Research Rept. No. 150, U.D.C. 622.411.51: 539.215, 1958. 52. Connor, P., W. H. Hardwick, and B. J. Laundry. Determination of Particle Size by Beta-Back Scattering, Journal of Applied Chemistry, London, 9: 525-531, 1959. 53. Hyatt, E. C., H. F. Schulte, C. R. Jensen, R. N. Mitchell, and G. H. Ferran. A Study of Two Stage Air Samples Designed to Simulate the Upper and Lower Respiratory Tract. Proceedings: 13th Interna-, tional Congress on Occupational Health. New York: Bookcraftsman Associates; Inc., pp. 486-503,1961. 54. Bugden, A. R. and R. J. Hamilton. Field Trials with the L.R.T.P. Densitometer. Mining Research Establishment, National Coal Board, Report No. 2209, 1960 Research Programme Reference No. 2.5, 1962. 55. Anderson, F. G. A Technique for Counting and Sizing Dust Samples - With a Microprojector, Americun Industrial Hygiene Aa_sociation Journal, Vol. 23: 330-336,1962. I 4 96 1 -= 97

CHAPTER V Medical Study GENERAL PROCEDURES THE MEDICAL sTODY was undertaken to determine the prevalence and severity of silicosis in employees of underground metal mines. The study was based primarily upon standard size roentgenograms of the chest, supplemented by medical and occupational histories, and selected tests of pulmonary function. In an attempt to sample a large segment of the metal mining population within a limited time, it was decided not to undertake complete physical examinations or clinical laboratory studies. As medical data other than the brief medical histories were not obtained prior to or after the time of examination at the mine site, there was no study of the development or progression of the disease. _ PERSONNEL AND FACILITIES Medical examinations were made at each mining location by a field - team using mobile equipment. The team consisted of a physician who completed the medical and occupational_ history and screened, the X-ray films as to quality, an X-ray technician for taking and process- ing the chest roentgenograms, a technician for the pulmonary function testing, and an administrative assistant for general administrative and clerical functions. During the 3 years the team was in the field there was occasional turnover and replacement of personnel, but every effort was made to insure a continuity of upiform procedures. The mobile equipment consisted of a self-contained X-ray truck and generator with equipment for developing, washing, and drying the exposed films. A viewbox was used to screen the films for satis- factory quality, so that workers with unsatisfactory films could be brought back for reexamination.- The second vehicle was a house- type trailer fitted with an office for the physician and a laboratory for pulmonary function testing. Logbooks and printed forms were available for recording all phases of the medical examination. 99

MINES STUDIED In general, it was planned to conduct medical examinations at each mine where an environmental study was made. However, this was not possible in all instances. An environmental study was com- pleted at 59 underground metal mines (nonuranium) and 8 uranium mines representing a total of 67 mines. Medical examinations were made at 50 metal mines. Nine metal mines'were not included for the following reasons : two mines were closed before the medical team arrived; one mine was at a site inaccessible to the X-ray truck; one mine declined to particiapte in the medical survey after the environ- mental study was made; the mining operations of one corporation were considered as four separate mines for the environmental study and as two mines for the medical survey; and three mines where the environmental study was conducted had no medical examinations although a separate study of past X-ray readings and work histories was made at one of these mines. The 8 uranium mines included in the engineering study, although not identical with the more than 150 uranium mines which had some workers examined ir} the medical study, were thought to show the type of conditions which might be encountered. EXAMINATION PROCEDURES Those employees who volunteered to participate in the study were asked to present themselves according to a prearranged schedule to avoid crowding and undue waiting. In most instances, examinations were limited to off-duty periods, although in some cases, employees were allowed to visit the unit during workiing hours. The entire examining procedure took about 20 minutes per mail. Each participant was advised at the outset that the medical findings on individuals would be held in the strictest confidence and would not be divulged to the employee, the employer, the union or others outside the Public Health Service. It was explained, however, that should the chest roentgenogram reveal a condition which was thought to need immediate medical attention, the employee's personal physician wouldd be notified if the Public Health Service was so authorized by the employee. Following the explanation of survey policy, each participant was asked for certiin basic information. A brief medical history was then obtained. Although no physical examination was performed, height and weight were measured. A complete occupational history was recorded and the prescribed pulmonary function tests and chest roentgenograms were completed. THE POPULATION SAMPLE EXAMINED The final decision as to whether a worker would present himself for examination was a matter for individual choice. The benefits to be derived from entering the examination program were carefully ex- plained to all the men, but no coercion was applied. Rosters including the names of all workers were supplied to the examining team. These lists were kept up to date as the status of individual workers changed. At the 50 metal mines studied there were 17,208 workers eligible for examination. Of this number, 13,181 or 76.6 percent presented them- selves for examination. The proportion of the total eligible workers who came for examina- tion was 90 percent or over at 8 mines, from 80-89 percent at 19 mines, 7 0-79 percent at 12 mines, and less than 70 percent at 11 mines. One way to learn if the workers who came for examination had dif- ferent characteristics from those who did not come in was to study the age distribution of the two groups. This type of analysis was pos- sible using the available records from 36.mines which included 71 percent of all workers. Table V.1 shows the percent according to age of all eligible workers who were examined. It will be observed that from 25 through 59 years of age three-fourths of the workers were examined. A smaller percentage of the younger men were included. Men 60 years of age and over were very slightly under-represented compared with the middle age group. Among underground workers 72.1 percent were examined as com- pared with 78.4 percent for surface workers. The difference was con- centrated in the groups under 50 years of age, while for workers above this age the percent of underground and surface workers examined was nearly the same. - - There was a tendency for men to transfer from underground to sur- face work as they become older and less fit for hard labor, but if any large group of potentially silicotic older men failed to appear for examination this table does not indicate it. Apparently a wide variety of factors influenced the decision of the workers to take or not take the physical examination. A major reason for nonparticipation was absence from work at the time of the survey because'of vacation, temporary ill.ness or other reasons. Failure to come for examination was frequently attributed to the use of carpools for commuting workers. In many instances, one man would not wish to delay the other members of his carpool. Sometimes men refused to come when they learned it was to be on their own time. Other men had a dislike and suspicion of any medical examination. A determined effort was made by the medical team to get all workers to come for examination. Management and union help was solicited and various publicity methods were used. i - _ 100 , - 101

TABLE V.1.-Workers at 86 metal mines who were eligible jor a medical examination and those examined according to age and place working Allworkers Underground workers Surface workers Age in years Total eligible Examined Total eligible Examined Total eligible Examined for ezamina- for examine- for eaamina- tion Number Percent tion Number Percent tion Number Percent Total_____________ 11,666 8,586 73.6 8,881 6,403 72.1 2,785 2,183 78.4 Less than 20_____________ 161 79 49.1 122 53 43.4 39 26 66.7 20-24 __________________ 951 593 62.4 793 477 60.2 158 116 73.4 25-29 __________________ 1,307 944 72.2 1,103 772 70.0 204 172 84.3 30-34 __________________ 1,690 1,306 77.3 1,408 1,069 75.9 282 237 84.0 35-39 __________________ 1,574 1,187 75.4 1,266 942 74.4 308 245 79.5 40-44 __________________ 1,670 1,280 76.6 1,277 955 74.8 393 325 82.7 45-49 __________________ 1,585 1,189 75.0 1,137 832 73.2 448 357 79.7 50-54 __________________ 1,338 996 74.4 933 692 74.2 405 304 75.1 55-59 __________________ 822 619 75.3 529 397 75.0 293 222 75.8 60 and over______________ 568 393 69.2 313 214 68.4 255 179 70.2 NI~1"N~N''~l!"II~'tilq4~!1f MqArf ~II P~'yIIPI .,, I¢'~ pll,u~ p I',dl"' Aql. I I ', I Iq~ I I u , I ~i , 11 ', :q i~ i, !II' , Q~, I"I~JI/li,l'~y III

PROCEDURE OF MEDICAL EXAMINATIONS MEDICAL HISTORY AND SYMPTOMS Each participant was questioned as to present or past history of the following disease conditions : tuberculosis, ' pneumonia, pleurisy, bronchitis, asthma, heart trouble, rheumatic fever, rheumatism, lead poisoning, "dust on your lungs," and mercurial poisoning. It was felt that the answers to these questions would be helpful in evaluating the chest roentgenographic findings. In addition, each worker was asked whether he ever noted wheezy or whistling sounds in his chest and, if so, whether these sounds occurred only with colds or at other times as well. Frequency of chest colds attended by sputum produc- tion was also recorded. Finally, a complete history of severity and duration of each chest illness necessitating absence from work during the previous 3 years was elicited (see figure V.1). The symptom of breathlessness was evaluated in each case through obtaining answers to a series of questions similar to those designed by British investigators,l * for the purpose of quantitating this sub- jective complaint. FIGURE V.1.-Medical examination form Medical hdatory and aymptoma Have you ever had, or been told you had: -~ (If YES, check and give year or years) a. Tuberculosis g. Rheumatic fever b. Pneumonia h. Rheumatism . c. Pleurisy i. Lead poisoning _ d. Bronchitis j. Dust on your lungs _ e. Asthma k. Mercurial poisoning f. Heart trouble Remarks Does your chest ever sound wheezy or whistling? YES NO If YES, only with colds? Or at other times? If you get a cold, does it usually go to your chest? YES NO (NOTE to esaminer: Only record YES it more than half of colds are followed by cough and sputum. For those who never get colds, record NO ; for those who only have chest colds, record YES.) During the past 3 years, have you had a chest illness YES NO which has kept you in bed, off work, or indoors at home? If NO, check, not even flu? *Numbers refer to list of references at the end of the chapter. 104 If YES, give : Doctor's diagnosis, if known Duration in days Year Queattons on breathlesaneaa Are you troubled by shortness of breath? YES NO Check: Not even on hurrying on level or walking up a slight hill? If YES : Do you have to walk more slowly than men of your YES NO own age when climbing hills or stairs? Do you have to walk more slowly than people of your own age YES NO on the level? Do you have to stop for breath after walking 100 yards or . YES NO after walking a few minutes on the level? Do you get short of breath while talking or undressing, or YES NO are you ever too short of breath to leave the house? -- -- - - GRADING OF SHORTNESS OF BREATH (after obtaining above answers) CIRCLE ONE a. Is breath as good as other men of his own age and build 1 at work, on walking, and on climbing hills or stairs? b. Is patient able to walk with normal men of own age and 2 build on the level but unable to keep up on hills or stairs? c. Is patient unable to keep up with normal men on the level, but able to walk a mile or more at his own speed? d. Is patient unable to walk more than about 100 yards on the level without a rest? e. Is patient short of breath on talking or undressing, or or unable to leave his house because of shortness of breath? OCCUPATIONAL HISTORY Starting with his present job, each worker was asked to recall to the best of his ability, the type, geographical location, duration, dust control measures, and environmental conditions of each previous job. Within the limitations of this method of personal interview, it was hoped to obtain a reasonably valid and complete work history from every participant. This information was recorded as seen in figure V.2.- - 105 I

FIGURE V.2.-Occupational history form Present job: Dates : From : 1954 to 1958. Name of mine or company : Acme Mining Co. Town and State : Tall Pine, Idaho. Kind of mine or industry : Lead-zinc. I. Your job : hfiner-S,quare 8et stope. II. Actual work done : All mining ta8k8. III. Special conditions : Wet drilling--rcechanical ventilation. Previous jobs: Dates ; From : 1946 to 1954. Name of mine or company : A3am Mining Co. Town and State: Centralia, Ariz. Kind of mine or industry : Copper. I. Your job: Motorman. II. Actual work done : Chute pulling. III. Special conditions : Muck dry, natural ventilation. Dates ; From : 1940 to 1946. Name of mine or company : Town and State: Various locations-Colorado. Kind of mine or industry : Ranch land. I. Your job : II. Actual work done : III. Special conditions : CHEST ROENTGENOGRAMS A 14- by 17-inch chest roentgenogram was taken of*each partici- pating worker. These films were taken using a 200-milliampere mo- bile unit fitted with a 1.5-mm. aluminum filter. Each film was taken at 72 inches with the worker in a posterior-anterior position. Ex- posed films were developed in the unit, usually at the mine site, and immediately screened by the team physician. In cases where the film was thought to be technically unsatisfactory, the worker was con- tacted when possible, and asked to return for a repeat roentgenogram. If preliminary screening revealed a condition which was thought to be of such a nature as to require immediate medical attention, such as suspect cancer or active tuberculosis, the participant was advised to see his personal physician. All films were then sent to the Occupa- tional Health Research and Training Facility at Cincinnati for recording and distribution to the panel of radiological consultants. PULMONARY VENTILATORY FUNCTION TESTS Two simple pulmonary function tests were performed by eachh par- ticipant unless maximal respiratory exertion was thought by the team physician to be contraindicated. These tests were obtained by a tech- nician who had been trained to urge the maximum effort for each subject. His work was frequently observed by the team physician in an effort to assure a high standard of performance. Test results which were thought to be technically unsatisfactory were so labeled. The two tests that were performed were the forced expirogram and the maximum forced expiratory fiow rate. The forced expirogram was obtained with the use of a 6-liter Collins recording vitalometer. Forced vital capacity and 1 second forced expiratory volume were measured using this method. In addition, the ratio of 1.0 sec. FEV/ FVC was calculated. The maximum forced expiratory flow rate was measured by means of the peak-flow meter described by Wright and Mc$errow.' Forced Expirogram Following an explanation and demonstration of the test by the technician, the subject was asked to take a maximum inspiration, place the mouthpiece of the recording vitalometer well into his mouth and blow out as hard and as fast and as long as possible. The sub- ject was repeatedly urged to obtain his maximum effort. The test was repeated several times in order to obtain three satisfactory re- cordings. From the resulting kymograph tracing, the forced vital ) capacity (FVC) and first second forced expiratory volume (FEV:L were calculated. Of the several tracings obtained, the one curve demonstrating the best FVC was used in calculating FVC, 1 second FEV, and FEVl/FVC. Maximum Forced Expiratory Flow Rate This test of maximum flow rate or peak expiratory flow (PEF) was accomplished by asking the subject to take a deep_ breath,as for the- forced spirogram, place the mouthpiece * of the' instrument into his mouth, and then to blow into the instrument as hard as he could. The results of the test were read directly from the dial as liters per minute and recorded. The test was repeated several times and the best effort taken as the subj ect's final score. iT_he disposable mouthpieces provided for the Collins vitalometer were also used for this test with the peak-flow meter: The internal diameter of the mouthpiece was three-fourths inch. 106 ~' 107

Conditions of Testing It is emphasized that these tests were made under field working conditions in a house-type trailer, and at the various mine sites in different parts of the country as previously described. Ample time for careful training and testing of the metal mine workers was avail- able during some working schedules, while others were necessarily somewhat hurried owing to uncontrollable circumstances. All workers were repeatedly urged to make their best effort. The ambient temperatures within the trailer were not utilized in the calculations of the pulmonary function measurments, but they were usually about 25° C. Since temperature corrections were not made, the values ob- tained included some degree of error. However, since this error was introduced in all measurements, the comparisons between groups of subjects were not affected. Temperature control was facilitated by scheduling the visits to mines in northern states 'in the summer months, and to the southern states during the winter. Workers were tested at all times of the day with relation to the working shifts but principally before or after the daily work shift. Analyses of the pulmonary function data could not be completed satisfactorily in time for the preparation of this publication, but certain preliminary analyses and interpretations based upon a simple multiple regression calculation technique are presented in appendix A. CHARACTERISTICS OF WORKERS EXAMINED AGE AND OCCUPATION Tables V.2 and V.3 show the age of metal mine workers according to principal occupation and present occupation. The principal occupa- tion was the type of work performed during more than half the time a man was engaged in metal mining with the additional provision that all persons who worked 10 years or more at the mine face were classified as face miners. The present occupation represented the kind of work a man was doing at the time he was interviewed for the medical examination. Excluding persons who had not worked steadily at any'one job, the principal occupation for almost three- fourths of the workers was located underground. Workers according to principal occupation were distributed as follows : Underground face, 47.1 percent; underground transportation, 11.2 percent; under- ground maintenance and construction, 10.4 percent; other under- ground work, 5.9 percent; surface transportation, 2.7 percent; surface maintenance and construction, 9.5 percent; surface mill, 6.9 percent; and other surface workers, 6.3 percent. I a s I 108 ~ 199

. TABLE V.2.-Principal occupation of workers at 50 metal mines* according to age TABLE V.3. Present occupation of workers at 50 metal mines* according to age -9 Principal occupation Total Age in years -i Age in years . Under 35 36 44 41Fb4 55 and over Present occupation Total Under 35 I 3b44 I 45-54 b5and over Number Number Total------------------ 12 487 4 136 3 627 3 184 1 540 , , , , , Total------------------ 12,487 4,136 3,627 3,184 1,540 Underground total_______ 8,435 2,792 2,659 2,127 957 Underground total_______ 8,838 3,179 2,672 2,116 871 Face------------------------- 330 5 728 1 1 678 332 1 592 , , , , Face------------------------- 4,474 1,788 1 474 943 269 Transportation________________ 1,265 473 359 307 126 Transportation________________ 1 468 564 , 413 350 141 Maintenance and construction_ - 1,171 381 321 312 157 Maintenance and construction__ , 1,818 505 468 518 327 Other underground work_______ 669 210 201 176 82 Other underground work_______ 1,078 322 317 305 134 Surface total__ ______ __ 2 870 755 790 833 492 _ _ , Surface total____________ 3,649 957 955 1,068 669 Transportation________________ 307 85 106 82 34 Transportation________________ 424 108 143 113 60 Maintenance and construction _ - 1,074 242 280 347 205 Maintenance and construction _ - 1 404 340 350 456 258 Mill------------------------- 777 249 190 224 114 , Mill------------------------- 898 300 207 245 146 Other surface work ____ ___ _ 712 179 214 180 139 __ _ _ Other surface work____________ 923 209 255 254 205 No principal occupation________ 1,182 589 278 224 91 ~ Percent ~ Percent Total------------------ 100.0 33.1 29.1 25.5 12.3 Total------------------ 100.0 33.1 29.1 26.5 12.3 Underground total___-___ 100.0 36.0 30.2 24.0 9.8 Underground total_____-_ 100.0 33.1 30,3 25.2 11.4 Face------------------------- 100.0 40.0 33.0 21.0 6.0 ' Transportation________________ 100.0 38 4 28 1 23 9 9 6 Face------------------------- 100.0 32.4 31. 5 25. 0 11. 1 . . . . Maintenance and construction__ 100.0 27 8 25 7 28 5 18 0 Transportation________________ 100.0 37.4 28. 4 24.2 10.0 Other underground work____ 100 0 . 29 9 . 29 4 . 28 3 . 12 4 Maintenance and construetion_ - 100.0 32.5 27.4 26.7 13.4 ___ . . . . . Other underground work_-____- 100.0 31.4 30,0 26.3 12.3 Surface total__________-_ 100.0 26.2 26.2 29.3 18.3 Surface total_.--_---____ 100.0 26.3 27 5 29.0 17 2 , . Transportation_______-________ 100.0 25.5 33.7 26.7 14. 1 Maintenance and construction 100 0 24 2 219 32 5 18 4 Transportation________________ 100.0 27.7 $4. 5 26.7 11 1 _ - . . . . . Mill------------------- 100 0 33 4 23 1 27 3 16 2 Maintenance and construction _ - 100.0 22.5 26.1 32.3 19 1 ------ . . . . . , Other surface work-___________ 100.0 22 7 27 6 27 5 22 2 Mill------------------------- 100.0 32.0 24.5 28.8 14.7 . . . . Other surface work____________ 100.0 25.1 30.1 25.3 19.5 'Excludes uranium mine workers No principal occupation________ 100.0 49.8 23.61 18.9 7.7 . I •Excludes uranium mine workers. 110 Age distribution by principal occupation shows that surface workers were older than underground workers : 17.2 percent as compared with 11.4 percent were 55 years of age and over. Faceworkers, and under- ground and surface transportation workers, had a small proportion in the oldest age group. Maintenance and construction workers, both underground and on the surface, milIworkers, and miscellaneous sur- face workers showed a relatively large percentage 55 years of age 111 707-103 0;fi4-9

and over. Similar age trends were observed when these workers were classified by present occupation. • The most marked difference was the greater percent of young men currently employed as faceworkers. This was due in part to the fact that all men with 10 years or more at the working face were classified as faceworkers in regard to their principal occupation. YEARS IN PRINCIPAL OCCUPATION Table V.4 shows the number of years that men had worked at each of eight principal metal mine occupations. Workers with the longest metal mining experience were found in surface occupations which showed 11.1 percent of the total with 30 years or more, compared with 8.3 percent for the same duration group among underground workers. The percent of employees with 30 years or more of experience was 13.8 for surface maintenance and construction workers, 13.4 percent for miscellaneous surface workers, 12.6 percent for miscellaneous un- derground workers, 9.2 percent for surface transportation workers, 8.6 percent for underground faceworkers, and less than 7 percent for un- derground transportation and maintenance and construction workers and surface millworkers. Approximately one-fourth of the underground transportation, maintenance and construction, and miscellaneous workers had less than 5 years of metal mine experience. Among surface workers only those in the mill had a similarly short experience. Otber surface occu- pations each had less than 18 percent in the under-5-year group. YEARS IN PRESENT OCCUPATION Table V.5 shows that nearly half (47 percent) of all underground workers had been at their present job for less than 5 years. A smaller proportion of surface workers (38.7 percent) had been in their job less than 5 years. Persons on the surface had been at the same job longer than those underground. Except for millworkers more than one-fifth of the workers in surface occupational groups had held their present job for 15 years or longer. From 10.7 to 14.9 percent of the groups of underground workers had 15 years or longer in the same occupation. 112 1 113

TABLE V.4.-Principal occupations of workers at 50 metal mines* according to years worked at metal mines Years at msta1 mines Principal occupation Total I -5 I 5-9 1 10-14 1 1 9 r19 1 20-24 I 25-29 39-34 I 35~ Number Total------------------------------- 12,487 2,838 2,573 22169 1,814 1,350 666 555 522 Underground total____________________ 8,435 1,730 1,817 1, 557 1,245 937 444 390 315 Face-------------------------------------- 5,330 909 12180 1,101 773 612 292 259 204 Transportation----------------------------- 1,265 336 276 198 196 119 57 42 41 Maintenance and construction_______________ 1,171 319 250 166 182 125 48 41 40 Miscellaneous______________________________ 669 166 111 92 94 81 47 48 30 Surface total_________________________ 2,870 542 606 463 452 314 174 135 184 Transportation----------------------------- 307 47 69 58 55 33 17 10 18 Maintenance and construction_______________ 1,074 175 217 181 161 119 73 62 86 Mill-------------------------------------- 777 199 171 113 140 70 36 21 27 Miscellaneous______________________________ 712 121 149 111 96 92 48 42 53 No principal occupation_____________________ 1,182 566 150 149 117 99 48 30 23 Face------------------------------------ Transportation----------------------------- Maintenance and construction--------------- Miscellaneous------------------------------ Surfacetotal------------------------- Transportation----------------------------- Maintenance and construction_______________ Mill-------------------------------- l' ---- Miscellaneous------------------------------ No principal occupation--------------------- °'Ezcludes uranium mine workers. ~I~'ll'u ~IN I'fl,plll~1 I I I I~i~;fl ~,;4II I14~'' I i'~"p I ~ll"i,lt ,I'I'9 IaIC {l~lll MP61~' 'I i~ ~II' Ik"~~ ' FA~IIlN~b~r~~lurl li~ Percent 100.0 22.7 20.6 17.4 14.5 10.8 5.3 4.5 4.2 100. 0 20.5 21.5 18.5 14.8 11. 1 5.3 4.6 3.7 100.0 17.1 22.1 20.7 14.5 11.5 5.5 4.8 3.8 100.0 26.5 21.8 15.7 15.5 9.4 4.5 3.4 3.2 100.0 27.2 21.3 14.2 15.5 10.7 4.2 3.5 3.4 100.0 24.8 16.6 13.8 14.1 12.1 7.0 7.1 4.5 100.0 18.9 21.1 16.1 15.8 10.9 6.1 4.7 6.4 100.0 15.3 22.5 18.9 17.9 10.7 5.5 3.3 5. 9 100.0 16.3 20.2 16.9 15.0 11.0 6.8 5.8 8. 0 100.0 25.6 22.0 14.6 18. 0 9.0 4.6 2.7 3. 5 100.0 17.0 20.9 15.6 13.5 12.9 6.7 5.9 7.5 100.0 480 12.6 12.6 9.9 8.4 4.0 2.5 2.0

116 UJ r.; 0 116 0 10 Ntr u6 -.41 n ec N ~4 wNi.o 06 C6 16 ~ ~ . 9i M w ONUJN ccornw b Od Z4 Od ~6 Cd Od +-iCOiC ti ti N ~ O to 00 ko M ~ O t- ..cc -44 .~ i ~ ~ eO1""~" s ~ ~ ~ ~ ~ ~ a w i b 0 ~ 0 N cooocmM 1.: °ic3.ri N * N N 00 N 00 00 wo V cV N GM N ~ ~ 0 0 n o c~ o n d rn ~/ c~ N i 1~ t1: C4 0i 0; m V In w w Od CM 6 q ~d ~ M C9 10 CM ~ 0 o oooo 0 0000 ~ ~ ~ ~ 9 °o ~ ~ °ol Sgg°o b ~ o °o °o g ~...,~.1 ~ ~ ~ a M r 'W t0 O M co u~o Ow M 00 cD N "tl ~ ~ 0 c ~ ~ N O M t- I I~ i 3 F 00 ~ o~rnoo u'J ee w ', 00 ac m ,-+ t" O h W N w<no.-~ o~0 con 1_ .1 N - to 1c`r~ OcDM 0 GV N ~ N N I .--1 ~ ~ ~ aot~c»c» o~co~ cl -0 Cw - 00 88 00 %4 00 00 00 hCO+-ih W d 00 O -i .-i °'w w o°'o ~ 00 .-~ 00 O M c0 O d+ - O 00 +^'i M GVN t~ wo11 ~ w w m S cq d " coco W d~ W ONi .-i ~ 1 1 1 ~ 1 ~ 1 ~ 1 1 ~ 1 ~ ~ 1 ~ 1 1 1 ~ 01 0 0 i V I V y I N 1 ~ 1 y 1Ut 1 ~ i ;~ ~ V 1 1 f7 ~ , 1 a a C1 1 ~ a d v 8 ANALYSIS OF MEDICAL FINDINGS- ANALYSIS OF CHEST .ROENTGENOGRAMS General Procedure The chest roentgenogram is the most important diagnostic tool for determining the prevalence of silicosis or most other types of pneumo- coniosis in a study of an industrial population. It was recognized that a careful and complete clinical study is necessary to appraise the nature and degree of pulmonary disease and associated disability in a given individual and should be made in hospitals and clinics where such medical evaluations could be made. Nevertheless, esperience over the past several decades has shown that an X-ray survey in an industry with a pneumoconiosis-producing dust hazard 'can give_ an accurate cross-section index of workers with the characteristic X-ray film changes associated with the disease. In view of the importance of obtaining impartial and highly ez- perienced physicians to read and interpret the chest roentgenograms obtained in this study and to insure a minimum of error in film inter- pretations, a panel of three highly qualified radiologists was selected for the purpose. It was agreed that each would read and classify each chest film independently without any knowledge of-the miner or his occupational history and submit their individual findings for collation and analysis. Quarterly meetings of the panel were held to discuss and resolve any areas of disagreement resulting from the in- dividual readings. Finally a group reading or consensus was entered on the records for each film. If any disagreement persisted, a majority reading was entered. Classification of Roentgenograms In earlier studies of silicosis and other types of pneumoconiosis made by the Public Health Service, several X-ray classifications of pneumoconiotic chest films had been developed or adapted for the purpose. These classifications were described in some detail in Public Health Service bulletins reporting studies of granite cutters published in 1929,9 pottery workers in 1939,4 of metal mine workers in 1942,6 of anthracite miners in 1936,8 of soft coal miners in 1941,° and workers in the diatomite mining and processing industry in 1958.8 In the present study, the panel of radiological consultants agreed to classify pneumoconiotic changes appearing in the chest films accord- ing to the newly revised "International Classification of Persistent Radiological Opacities in the Lung Fields Provoked by the Inhalation of Mineral Dusts." This revised international classification was 117

adopted at a meeting of experts in 1958, and was published and pro- mulgated by the International Labour Office early in 1959.9 Sets of I.L.O. standard reference chest films illustrating the various cate- gories of pneumoconiotic changes were distributed for use when they became available. The use of this descriptive classification permits a comparison of the nature and degree of pneumoconiotic changes between employees, industries and also between countries, thereby facilitating epidemio- logical studies of pneumoconiosis problems and the evaluation of pub- lic health programs for prevention of these dust-induced pulmonary diseases. The I.L.O. classification is not intended to define pathologi- cal entities, or to take into account the question of working capacity. It has no relation to the legal definition of stages of pneumoconiosis for compensation purposes. (See ch. VIL) A slightly modified schematic representation of the 1958 I.L.O. classification is shown in figures V.3 and V.4. All the films in this study were classified according to this detailed scheme. In presenting the data for the purpose of this report, the film readings were presented in four broad groupings according to their relative degree of medical significance. These groupings were as follows : Negative films or no pneumoconiosis-healthy or normal chest. Suspect films-"suspect,D7 "doubtful," or "borderline" silicosis.* Small opacities including categories 1, 2, and 3-simple silicosis.* Large opacities including categories A, B, and C-complicated silicosis.* It should be emphasized that these groupings were based upon ob- jective chest film interpretations and were classified by a panel of three experienced radiologists who had no knowledge of the individual miner's occupational history, medical history, or physical condition. The classification is not intended to imply any degree of physical disability or to define pathological entities. The classification does indicate that the films are consistent with a diagnosis of simple or complicated pneumoconiosis. Roentgenograms Classified as Silicotic In this study, a grand total of 14,959 persons appeared for medical examination•. Satisfactory chest roentgenograms were obtained upon 1.4,858 of these persons. Of these films, 522 were classified by ther radiological panel as consistent with a diagnosis of silicosis, resulting in a crude rate of 3.5 percent for all 14,858 X-ray readings. In analyz- *Although the I.L.O. classification always uses the generic term "pneumo- coniosis", the term "silicosis" is generally used in reporting the results of this study since silicosis is the type of pneumoconiosis commonly found in metal miners exposed at mining operations in hard rock and silica-bearing ore bodies. ~ •3oadsng 2 ~ ~ w •aAlJcsod ~ q ~ U .~ w ~ ~ q U .~ 0 ~ r4 ~ ~ .~ ~ 9 d .o ~ x e a ° N ~ a .2 90 ~ a m 8 a 0 .ry a. M wC. ~3oa ~ A j4 a a. ~ ~ F 0 N ~ i•aQa ~ a ~ 0 ~ . ~ a« 86ag w a ;4 ~ ~ 0 ~-- ~ ~ 0 a 0 0 9 .t ~° ~ W ~ N ~ ro ~ ~ zal 0 ~ ~ 0 0 'ultS aooa ' ~ ~ ~ ~ b ~ a ~ u q ~ W ~SO'}aB;sl'}B$un .~m 0 ~ ~ 8 ~ . ~ ? q wR~ m '7 ~ 0 ~ ~ ~ ~ ~ ' 4 ~~ b06 pd ~ ~ w ~ ~ y ~ Ws ~ ~ ~ a~ ~ w ~ m ~ 3~ ~ a 0 3~ o a. ~x... ,c,d ~ a ro ~ 0? ~ 118 ~ 119

~ w ~ 120 o 0 m .~ p o ~ a 60 o ~ N d p .i. y T, °y~ 8~ F N"'d" m ~ 'G N U 'G o c~ ~ ° O G7 L7 a~ CO d F 4 ° .d d O O ~ ~ .~y O C a y d ~~ ~ ~ B 2+ ~ ~~~a o 0 ° ao O~°00 ~ ~ i~'~ v q'b o0 Q1~ ~ n o e ~ ~ ~ ~ ~~ ~ ~ ~ ~ 8~ . b ~ a a o eu tia q ~ q ~ o~<q~ ~y § q q q ~ O o•~ o ° m '° aai ~ ~ 4~ m^a~eo 2 03 CS ~ "Og ~~o G ~~~~ ~~o "~ ~ a d Bd i~ p F ~a aa °>Ud21 Gd F ~ ~~8 a 61 ~ v O ,~ay mc~-j d~ , d 3 a~ d . ' ' a o b N a) N p N ~a ~ tJ a ~~ ~ W~ U •d •a ,~ „ 'a ~. . d ...d .a .. ~ a 'a~ fn y~ U° F7 q ~ ~ ~y ~ W F R Fi ~ O W ~ ~-. ~ m F'i. b^ cyQ'OO ° q'.,~"~ ~ M R ~b q ~ ~° A~ G~~q ~ ° ' u~do ~° a o ° a ~ ~ a°*' d6pj~ ..~. t°i a t B ~ ~ o °'d °° 2 ai ° O'b •C a -~"~ . W° Q O w' LL V.O D Fi oU ola-~ FatdNR'~ ° ' Wa- oF y °.~1 B m ' . ~ i '- LOW . OoU ~aNFi.a ~ m A+a ° y N r~ o~ mti ,'~.° a F a~ N A ° ~ ~ a`"ib A a O t1ON ~ a ~ aoo C04 0 A Wo 'C~ OOW 4' a ~ m ~ a a o~ ~ aq ~ ` ° °~ ~ en~ B ~ °~ a~~ a 4 '~ d ~ G~7 ~°° ~ pFV a~doo d ~~/I~ am ~° 7 ~~~ Ca7W GId'0t p°'U . w .C ~~o~'~ R•~~° L om ~~ . ~op.vwa ro '~' f7 pp a W ' ~~ R .i c v ~ F 0 0 N U WW M FObO rn :5 m 'U U F~'Oy F i i-. VJ 0.Q . N ~+' cd m .y N~ U~N ~G$ N ~~ `~ ~ oo mo~o ^o ~° w aa" ~00~ ~ r . ° bn a~ ~ ~~~~~~oa~z ~o o ~ ~ ~ q ;N H~ ~ a° zI aa mw+'~- ~"' DC ~ ~ °~ o p b 5 H ~ a ~ H v w v ~ O ~ w p 8 F q4 i ~ a Q ~ e O O ~ ~ o ° ~ °D °° w 0 z A v~ a w t ing positive film readings, 337 or 2.3 percent of the total were classified as simple silicosis and 185 or 1.2 percent were considered to be com- plicated silicosis. The crude silicosis rate, therefore, for all metal mine employees examined was 3.5 percent, of whom about one-third were classified as complicated silicosis.* X-ray findings . on the total mining population examined in the study might not present a true picture of the prevalence of silicosis in the metal mines included in the survey. A rather common situation was the case of a silicotic miner who had also worked in other dusty trades such as coal mining, foundries, or smelters for substantial pe- riods during his working life. Therefore, persons employed for 5 or more years in other dusty work, were excluded from the study group upon which detailed analyses had been made. In all there were 883 persons out of the grand total of 14,959 ex- amined who were excluded from the study group for the following reasons: Workers with incomplete records------------------------------ 180 Workers considered nonminers------------.-------------------- 82 Workers with 5 or more years in other dusty work not related to metal mining- ------ ----------------------------------- 671 Total excluded--------------------------------------------- M The exclusion of these 883 persons including 46 cases of silicosis from the total group who appeared for examination leaves a study group of 14,076 persons who were considered to be bona fide metal mine workers. This was the sample population of metal miners upon which the following detailed analyses has been made. In certain tables the 1,589 workers in uranium mines have been excluded leaving a total of 12,487 men in 50 metal mines. The prevalence of metal mine workers with X-ray evidence of sili- cosis is shown in tables V.6 and V.7. Within the study group of 14,076 metal mine workers, there were 476 or 3.4 percent with chest films classified as silicotic. This ratio of positive cases varied greatly from mine to mine ranging from 12.9 percent at one mine to none at seven mines, the median figure being 3 percent. It is of considerable interest that 13 mines had less than 1 percent silicosis while only 5 mines had more than 7 percent silicosis. The remaining 32 mines were rather evenly distributed with crude percentage rates ranging from 1 up to 7 percent. Although the overall proportion of simple to complicated silicosis films in this group was roughly two to one, there was considerable variation from mine to mine. Another striking feature in analyzing these crude figures mine by mine was the paucity of silicosis cases at many mines and the heavy grouping of cases at a few other mines. * See prevalence rate of 3.4 percent for the study group, table V.7. 121

TABLE V.6.-Distribution of 60 metal mines* according to prevalence of silicosis Percentage range of silicosis cases Number Workers examined of mines Number Perceqt of total None--------------------------------- 7 1, 081 8.7 0.1-0.9--------------------------------- 6 1,829 14. 6 1.0-1.9-------------------------------- 7 1,584 12.7 2.0-2.9-------------------------------- 5 1,501 12. 0 3.0-3.9-------------------------------- 5 489 3. 9 4.0-4.9-------------------------------- 8 3,574 28.6 5.0-5.9-------------------------------- 2 400 3.2 6.0-6.9-------------------------------- 5 1, 138 9. 1 7.0-7.9-------------------------------- 1 (t) . 1 8.0-8.9-------------------------------- 0 ------------ ------------ 9.0-9.9-------------------------------- 1 (**) 3.5 10.0-10.9------------------------------ 2 283 2.3 11.0-11.9------------------------------ 0 ___________ -- ____________ 12.0-12.9- ----------------------------- _ 1 _ ( $) 1.3 •Excludas uranium mine workers. tLess than 60 workers. •*Between 400 and 600 workers. jBetween 100 and 200 workers. Figure V.5 shows the distribution of the number of simple and com- plicated cases on a mine-by-mine basis, ignoring rates based on mine population. Figure V.5 shows that seven mines had no silicosis. In addition to these, 14 mines had from 1 to 4 cases of simple silicosis but no com- plicated silicosis. Three other mines had no simple silicosis but two or three cases of complicated silicosis. Another grouping of 11 mines had from 1 to 4 cases of simple silicosis and also from 1 to 3 cases of complicated silicosis. Hence, a heavy concentration of silicosis cases occurred in the remaining 15 mines that had more than 7 cases of silicosis with a wide scattering of both simple and complicated cases. Table V.7 shows for each mine the percent of workers with simple and with complicated silicosis, the prevalence of silicosis among workers with 10 years or more and 20 years or more experience in metal mining, and the percentage distribution of persons examined according to years worked at metal mines. Mines were grouped ac-• cording to size, namely, those with less than 100 employees, mines with 100-299 employees, mines with 300-699 employees, and mines with 700 or more employees. Uranium mines, most of which had less than 25 employees, were placed under a separate heading. It may be noted that within each size group, individual mines showed great variation in the prevalence of silicosis. This was un- 122 TABLE V.7. Percent of metal mine workers with X-ra1y evidence of silicosis according to size of mine and number of years worked at 60 metal mines and uranium mines Percent of workers with siltcosis Percent of workers with specified According to type According to years worked at metal mines number of years of experience at metal mines Simple , Total o i- 10 years I 20 years Less than I 10 19 I 20 or over I ~i a or more or more 10 Total for all mines 3.4I 2.2I 1.2I 6.2I 11.6I 46I 31I 23 Mines with less than 100 employees Total 4.2 2.4 1.8 8.2 13.2 50 29 21 10.5 10.5 0 20.0 0 *47 *37 *16 7.7 7.7 0 7.7 *11. 1 0 *31 *69 6.7 1.7 5.0 12.5 21.4 47 30 23 6.5 4.3 2.2 10.5 21.1 38 41 21 4.3 1.4 2.9 9.7 13.3 55 23 22 3.7 0 3.7 7.1 18.2 48 32 20 3.0 3.0 0 3.3 5.3 *9 33 58 2.7 2.7 0 *12.5 *16. 7 79 *5 *16 1.8 1.8 0 4.5 0 61 25 *14 0 0 0 0 0 *43 52 *5 0 0 0 0 0 79 19 *~ Total 3.4 2.2 1.2 5.3 9.6 38 37 25 12.9 8.6 4.3 18.4 23.3 30 33 37 10.6 8.0 2.6 19.3 36.2 47 35 18 5.2 3.0 2.2 12.8 25.0 65 20 15 4.7 2.6 2.1 9.0 19.0 48 30 22 4.6 2.3 2.3 10.9 16.7 59 28 13 4.0 2.3 1.7 7.1 13.2 43 35 22 3.8 2.3 1.5 5.2 28.6 28 62 10 3.4 1.7 1.7 3.9 7.1 12 40 48 3.2 0 3.2 4.2 13.6 22 54 24 2.8 1.7 1.1 3.6 5.2 23 35 42 2.6 2.6 0 3.0 2.7 11 25 64 1.7 1.7 0 3.0 6.9 44 31 25 1.6 .8 .8 6.3 *33.3 76 20 *4 1.1 0 1.1 2.6 9.5 56 32 12 1.0 1.0 0 1.4 1.7 25 44 31 .7 , 7 0 0 0 50 33 17 .6 .6 0 .6 1.2 9 43 48 .4 .4 0 .7 2.2 39 42 19 0 0 0 0 0 42 53 0 0 0 0 0 36 55 0 0 0 0 0 27 31 1 1 123 Mines with 100-299 employees ~ a

TABLE V.7. Percent of metal mine workers with X-ray evidence of silieosis according to size of mine and number of years worked at 50 metal mines and uranium mines-Continued Total Percent of workers with ellteosis According to type Simple Compii- eated According to years worked at metal mines 10 years I 20 years or more or more Mines with 300-699 employees Percent of workers with specified number o metal f years of experience at mines Less than 10 10-19 20 or over Total 4 0 2.8 1.2 5.5 9.7 28 36 36 9.? 6.5 3.2 10.2 21.3 5 57 38 6.0 49 1. 1 6.0 6.9 *1 12 87 6.0 4 9 1. 1 10.5 24. 1 50 30 20 5.3 3.0 2.3 10.7 23.5 51 30 19 4 0 2.8 1.2 5.8 9.6 30 35 35 2.4 1.3 1. 1 3.3 6.4 27 39 34 1.4 7 7 3.4 8.3 62 22 16 9 9 0 1.0 1.6 5 38 57 3 3 0 .4 1.0 27 40 33 Mines with 700 or more employees Total 3.3 2.0 1.3 6.5 12.9 54 27 19 6.2 4.3 1.9 11.4 27.0 46 33 21 4 3 2.7 1.6 7.3 14. 4 42 35 23 4 3 1.5 2.8 8.9 19.1 52 27 21 4.0 2.5 1.5 18. 7 37.9 80 14 6 2.8 2.1 7 4-6 10.9 39 36 25 1.6 1.0 6 5.4 11.1 70 23 7 6 6 0 .6 .9 4 47 49 0 0 0 0 0 91 8 *1 0 0 I 0 0 0 90 7 3 Uranium mines 3.2 2.1 1. 1 10.3 27.3 70 21 9 •Based on less than 10 employees in exposure group. doubtedly due to many factors, some of which represented a genuine difference in the silicosis hazard while others were mere]y a reflection of the age and work experience of the population at risk. It is ap- parent that where a large proportion of the workers were in the older age groups with long mining experience the silicosis rate would be higher than in younger populations even though the risks were the 1 1 14 O cn O U J N 0 w ~ ¢ 12 8 6 4 2 0 1 2 1 1 1 1 7 2 8 2 2 2 2 1 2 1 1 1 1 1 1 1 1 1 1 1 1 4_ 6 8 10 12 14 ' 2 0 NUMBER OF CASES OF SIMPLE SILICOSIS P'iGURE V.5.-Frequency distribution of 50 metal mines showing number of cases of simple and complicated silicosis. same. For example, in this table the mines do not remain in the same position with regard to the relative silicosis hazard when silicosis prevalence for all employees is compared with the silicosis prevalence limited to men with 10 years or more of metal mining experience. One mine with a large proportion of short-time miners had an overall silicosis rate of 4.0 percent, yet for men with 10 years or over in metal mining the silicosis rate rose to 18.7 percent, much above the average. Table V.8, summarizing table V.7, shows a frequency distribution of metal mines by size according to the percent of workers with sili- cosis at each of the 50 mines. In each of the five silicosis prevalence groups there were one or more mines in the various size groups, except there were no large mines among those with 7.0 percent and over of silicotic workers. Thirteen mines had less than 1 percent of their em- ployees affected with silicosis; 12 mines-1.0-2.9 percent; 13 mines-- 3.0-4.9 percent; 7 mines-5.0-6.9 percent; 5 mines-7 percent €tnd over. 124 1 125

TABLE V.8.-Freguency distribution of metal mines* by size showing percent of workers with silicosis Total Number of mines by size Percent of workers with silicosis number of mines Less than 300 employees 300-299 employeees 300-699 employees 700 or more employees 0-0.9------------------------- 13 2 6 2 3 1.0-2.9----------------------- 12 2 6 2 2 3.0-4.9----------------------- 13 3 6 1 3 5.0-6.9----------------------- 7 2 1 3 1 7.0 and over ------------------ 5 2 2 1 0 *Excludes uranium mine workers. In considering the prevalence of silicosis among metal mine work- ers with 10 years or more of exposure, 8 of the 50 metal mines studied showed no cases of silicosis. There were 17 mines which had a sili- cosis prevalence of less than 5 percent, 12 mines had 5.0 to 9.9 per- cent silicosis, 9 mines had 10.0 to 14.9 percent silicosis, and 4 mines had from 18 to 20 percent with silicosis in these exposure groups. The crude rate for all silicosis cases, both simple and complicated, showed little difference according to size of mine. It ranged from 3.3 percent for mines with 100-299 employees to 4.2 percent at mines with less than 100 employees. There was a slightly greater variation with size when consideration was limited to silicosis prevalence among workers with 10 or more years of metal mine experience. Mines with 100-299 employees showed a silicosis rate of 5.3 percent and mines with less than 100 employees showed 8.2 percent. On the other hand, mines with 300-699 employees and mines with 700 or more employees had silicosis rates of 5.5 and 6.5 percent, respectively. HISTORY OF PAST ILLNESSES Chest Illnesses Table V.9 shows the history of past illnesses reported by each miner in reply to specific questions asked by the examining physician obtain- ing the medical history. The frequency of these illnesses is shown both by broad age groupings as well as broad groupings by years of em- ployment in the metal mining industries. A history of pneumonia was reported rather frequently in all age groups (14 to 40 percent) and showed a regular increase with increas- ing age and but little increase with years of mining employment. It did not seem appreciably higher in the silicotic groupings than the _ groups with normal* chest films. •The term "normal" in this section implies no radiologic evidence of silicosis. 126 f t A history of pleurisy was reported less frequently than pneumonia in the nonsilicotic mining group and showed little difference with in- creasing age after 35 years of age and increasing length of employ- ment, ranging from 5.1 to 15.2 percent. Among the workers showing evidence of silicosis, however, pleurisy was reported much more fre- quently (11.5 to 43.5 percent) but- showed no regular rising trend- with age and length of employment. A medical history of bronchitis was reported in a low proportion of all miners in the large nonsilicotic group, the rates ranging from 4.1 to 9.3 percent, and with only a slight indication of an increasing prev- alence with age and years of employment. It was reported only slightly more often in some of the silicotic groupings particularly among the younger silicosis cases. A history of asthma was reported in a consistently small propor- tion of all age and length of employment groups, ranging fram 2.1 to 7.8 percent, and increasing only slightly with age. It was only slightly more prevalent in the silicosis group and was not a common complaint. Tuberculosis A history of tuberculosis was reported infrequently by this- mining population. In the large nonsilicotic group shown in table V.9, the rates were consistently well below 1.0 percent for miners below 45 ' years of age (0.2 to 0.5 percent). Above this age, the rates were slightly higher but reached only 1.1 percent. Because of the small numbers, the percentage rates fluctuated in the silicotic age groups, but . the total cases reported were 14 out of 426 cases, or 3.3 percent, and ranged from 0 to 6.1 percent in the older age groupings. A review of these case records of the metal mine workers reporting a previous history of tuberculosis and a check against_ their chest film interpretations showed that a substantial proportion of cases had no definite evidence of pulmonary tuberculosis. Out of 65 case histories of tuberculosis among the nonsilicotics only 13 were found to have definite findings of a previous infection. Similarly out of 14 silicosis cases with a history of tuberculosis only 5 showed definite evidence of past infection. The remainder of the cases had ill-defined and vague histories and no present X-ray evidence of past infection. The above fibrures were based on miners giving a past history of tuberculosis: A more basic question is the actual prevalence of pul- monary tuberculosis as observed on the chest roentgenograms. As described previously, each film was read independently by t_h_e three radiological consultants_who_ in addition to classifying the film by the I.L.O. Classification of the Pneumoconioses, also added symbols - and comments signifying the presence of other abnormalities in the-' 127 707-403 0-64-10 _. i i i t

Tear.E V.9. Percent of aoorkers at 50 metal minest with certain present symptoms and past illnesses for silicotic and nonsilicotic workers by age and years worked at metal mines _ Number eaamined_______-__ Workers with sRicosis Number Age in years Under 35 1 3-44 1 45-54 1 55 and over Yeers at metal mines -10 1 10{- 1 -20 1 20+ 1 -20 1 20-29 3D+ 1 -20 1 20-29 1 30+ Workers without silioosis Past history: Pneumonia____________________ 538 93 644 92 386 210 84 95 89 154 Pleurisy---------------------- 178 68 339 68 199 145 43 42 49 79 Bronchitis_____________________ 153 27 175 26 110 62 29 24 35 35 Asthma----------------------- 92 15 122 23 80 48 14 21 19 40 Tuberculosis_______________-___ 17 2 16 1 9 10 2 4 3 1 Hearttrouble__________________ 65 14 75 14 68 36 17 26 25 57 Rheumatic fever_______________ 93 14 41 10 27 16 4 3 2 7 Rheumatism 105 35 256 57 251 151 51 70 86 134 Dust in lungs__________________ 27 12 82 24 65 93 25 14 34 40 Present symptoms: Chest wheezes: - With colds________________ 724 146 757 99 422 247 67 87 85 140 At other times_____________ 196 40 274 50 183 133 42 28 46 88 Chest illness in past 3 years_____ 738 127 666 91 286 200 61 49 68 114 Short of breath________________ 137 28 218 35 194 107 49 60 69 119 Number esamined___________ 3,482 654 3,130 448 1,665 1,024 311 375 381 591 Past history: Pneumonia____________________ Pleurisy---------------------- Bronchitis--------------------- Asthma----------------------- Tub'erculosis------------------- Heart trouble__________________ Rheumatic fever_______________ Rheumatism__________________ Dust in lungs__________________ Present symptoms: Chest wheezes: With colds________________ At other times_____________ Chest illness in past 3 years_____ Short of breath_______________ •See footnote at end of table. _..._.. ~ ,,. ~....,..~ ________ 5 3 12 22 18 3 17 33 ________ 3 10 9 22 8 3 8 19 ________ ________ 3 3 6 9 1 1 3 9 2 1 1 5 2 1 0 10 ________ ________ 0 0 1 5 1 0 3 4 ________ ________ 0 2 1 1 6 0 5 7 ________ ________ 0 0 1 1 2 0 1 2 5 5 9 19 4 7 9 36 ________ ________ 13 10 14 41 19 7 19 59 5 5 13 29 10 5 11 30 3 3 7 11 10 1 6. 27 4 4 8 18 16 2 9 27 6 2 11 26 3 5 17 49 ________ ________ 26 23 48 91 45 15 49 129 L4 I .0. - 'F. 1',.ia',

TASr.E V.9. Percent of workers at 50 metal mines* vn:th certain present symptoms and past illnesses for silicotic and nonsilicotic workers by age and years worked at metal mines-Continued Per cent ~ Age in years Under 35 35-44 ( 45-54 I 55 and over Years at m etal mines -10 1W- -20 I 2D-}- I -20 I 20-29 3D+ I -20 I Ee-29 I 30+ Workers wit hout sllicosis Past history: Pneumonia____________________ 15.4 14.2 20.6 20.5 23.2 20.5 27.0 25.3 23.4 26. 1 Pleurisy---------------------- 5.1 10.4 10.8 15.2 12.0 14.2 13.8 11.2 12.9 13.4 Bronchitis_____________________ 4.4 4.1 5.6 5.8 6.6 6.1 9.3 6.4 9.2 5.9 Asthma----------------------- 2.6 2.3 3.9 5.1 4.8 4.7 4.5 5.6 5.0 6.8 Tuberculosis___________________ .5 .3 .5 .2 .5 1.0 .6 1. 1 .8 .2 Heart trouble__________________ 1.9 2.1 2.4 3.1 4.1 3.5 5.5 6.9 6.6 9.6 Rheumatic fever_______________ 2.7 2.1 1.3 2.2 1.6 1.6 1.3 .8 .5 1.2 Rheumatism__________________ 3.0 5.4 8.2 12.7 15.1 14.7 16.4 18.7 22.6 22.7 Dust in lungs__________________ Present symptoms: Chest wheezes: .8 1.8 2.6 5.4 3.9 9.1 8. 0 3.7 8.9 6.8 With colds________________ 20.8 22.3 24.2 22.1 25.3 24.1 21.5 23.2 22.3 23.7 At other times_____________ 5.6 6.1 8.8 11.2 11.0 13.0 13.5 7.5 12.1 14.9 Chest illness in past 3 years _____ 21.2 19.4 21.3 20.3 17.2 19.5 19.6 13.1 17.9 19.3 Short of breath________________ 3.9 4.3 7.0 7.8 11.7 10.4 15.8 16.0 18.1 20.1 Past history: Pneumonia____________________ Pleurisy---------------------- Bronchitis_____________________ Asthma----------------------- Tuberculosis___________________ Hearttrouble__________________ Rheumatic fever_______________ Rheumatism__________________ Dustinlungs__________________ Present symptoms: Chest wheezes: With colds________________ At other times_____________ Chest illness in past 3 years_____ Short of breath________________ •Exciudes uranium mine workers. Workers with siiicosis ________ ________ 19.2 13.0 25.0 24.2 40.0 20.0 34.7 25.6 ________ ________ 11.5 43.5 18.7 24.2 17.8 20.0 16.3 14.7 ________ ________ 11.5 13.0 12.5 9.9 2.2 6.7 6.1 7.0 -------- -------- 7.7 4.3 2.1 5.5 4.4 6.7 0 7.8 ________ ________ 0 0 2.1 5.5 2.2 0 6.1 3.1 ________ ________ 0 8.7 2.1 1.1 13.3 0 10.2 5.4 -------- -------- 0 0 2.1 1.1 4.4 0 2.0 1.6 ________ ________ 19.2 21.7 18. 7 20.9 8. 9 46.7 18.4 27.9 ________ ________ 50.0 43.5 29.2 45.1 42.2 46.7 38.8 45.7 -------- -------- 19.2 21.7 27.1 31.9 22.2 33.3 22.4 23.3 -------- -------- 11.5 13.0 14.6 12.1 22.2 6.7 12.2 20.9 ________ ________ 15.4 17.4 16.7 19.8 35.6 13.3 18.4 20.9 .__----- ________ 23.1 8. 7 22.9 28. 6 6.7 33.3 34.7 38.0

chest roentgenograms. Evidence of pulmonary tuberculosis was rou- tinely noted excepting the healed primary complex or childhood type of tuberculosis (Ghon tubercle). Evidence of pulmonary tuberculosis, usually considered inactive or arrested, was noted by at least 2 of the 3 radiologists in 82 of the 13,600 nonsilicotic films, a frequency of 0.6 percent. Using the same criteria, tuberculosis was noted in 25 of the 476 films showing evidence of sili- cosis, a prevalence of 5.3 percent. In the former group of films, nine cases also had a previous history of tuberculosis, while in the silicotic group two cases gave a positive history. Heart Trouble A history of "heart trouble" was closely related to age. In the non- silicotic population, the percentage rates in the two younger age groups ranged from 1.9 to 3.1 percent. In the 45-54 year age group, the rates ranged from 3.5 to 5.5 percent and were slightly higher in the employees with the longest work histories. In the oldest age group, 55 years and over, more history of "heart trouble" was ap- parent with the rates ranging up to 9.6 percent. Longer employment also appeared to have a relationship in this older group. Within the silicotic groupings, the small number of cases made age and length of employment comparisons difficult. There did not seem to be any ex- cessive complaint of heart trouble in this population, however, based on 22 affirmative answers out of 426 silicotic cases, or 5.2 percent. All except two cases occurred over the age of 45 years. Rheumatic Fever A history of rheumatic fever was also reported infrequently in this mining population but somewhat more frequently in the younger age groups, the highest rate being 2.7 percent. It was reported among 1.6 percent of the silicotic population. Rheumatism The question regarding a history of "rheumatism" elicited a fre- quent positive response in all age and employment groups among the nonsilicotic workers but increased from a rate of 3.4 percent for all men under 35 years of age to 8.7 percent in the 35-44 age group, 15.1 percent in the 45-54-year age group, and 21.5 percent in the 55-years- and-over age group. Within each broad age grouping there was a slight trend toward increasing prevalence with increasing mining experience. In the relatively small silicotic population, however, a 132 positive history was more prevalent in the three broad age groupings and showed little relationship to length of mining employment aside from age. . . Dust on Lungs The reply to the question as to whether a miner had ever been told he had "dust on his lungs" was answered negatively in well over 90 percent of most age and employment groupings among the large uon- silicotic population. Affirmative replies in these nonsilicotic group- ings ranged from 0.8 to 8.9 percent, however, and showed an increas- ing prevalence both with increasing age and increasing years of employment. _ - Within the relatively small population actually found to have sili- cotic X-ray changes, however, 182 or 42.7 percent of the 426 workers with present X-ray evidence of silicosis stated that they had been so informed. This large proportion of affirmative replies in the sili- c cotic group did not appear to be related to age or length of employ- ment within this group. History of Lead Poisoning A past history of lead poisoning was reported by 82 metal mine workers. Further examination of the records of these men indicated that for 21, the lead poisoning episode had occurred at a time when they were not employed in metal mining. Tasks mentioned included spraying orchards, painting, making storage batteries, and welding and cleaning gasoline tanks. The remaining _ 61 men had suffered from lead poisoning while employed at metal mines. This constituted a prevalence of 0.4 per- cent of workers at all mines. If only, men working at mines which were producing lead when the present study was made are considered, there were found to be 26 men who reported having had lead poison- ing at some time in their past experience. This represents a prevalence of 0.7 percent as contrasted with 14 percent of the Utah metal miners who reported a history of lead poisoning when surveyed in 1939. Among 254 Utah metal miners examined in 1958, just 1 man reported ever having had leadpoisoning. If the 1939 rate had continued the expected number of men with lead poisoning would have been 36. The ... A, ~ great decrease in percent of men affected can be attributed to many factors, among which might be a change in the proportion of lead ores 11 mined (more sulfide and less carbonate ore, which is more likely, to cause lead poisoning). 133

The following tabulation shows the year when the last attack of lead poisoning occurred among the men questioned in the survey. Year of last lead poisoning Number of men Before 1935------------------------------------------------- 7 1935-1944 ----------------- ---------------------------------- 11 1945-1954 --------------------------------------------------- 22 1955 and later --------------------------------------------- 10 Unknown date----------------------------------------------- 11 TotaL-------------- -------------------------------------- 61 These figures indicate that, although lead poisoning among miners is becoming increasingly rare, there are still cases which have de- veloped within the past few years. Almost two-thirds of the mines studied revealed no workers with a history of lead poisoning. Only four mines reported more than three cases. The greatest number oc- curring at any one mine was eight cases. The majority of attacks of lead poisoning in recent years had oc= curred at the same mine where the miner was working at the time of the medical examination. Attacks in earlier years had usually taken place at a mine other than that at which the worker was currently employed. , History of Mercurial Poisoning Mercurial poisoning was very rarely reported among this group of miners. There were 23 cases which could apparently be attributed to exposure in metal mining occupations. Among 309 employees at mer- cury mines, 7 or 2.3 percent said they had been affected at some time with mercurial poisoning. Only three of these men indicated that the attack occurred at the same mine where they were examined. The remaining 16 men were not presently working at a mercury mine but had done so at some time in the past. A number of these men gave the name of mines where a mercury hazard was known to have existed. One-half of the cases, where the date was known, had taken place since 1950 and only one case had occurred before 1935. Some men reported having lost all of their teeth and some referred to intestinal symptoms. Three men, not included above, mentioned poisoning from the medicinal use of mercury salves. FRE(,ZUENCY OF PRESENT SYMPTOMS Chest Illness Table V.9 also shows the frequency of present symptoms reported in reply to the questions asked in taking the medical histories (fig. V.1). Roughly 20 to 25 percent of those examined reported that their 134 chests sounded "wheezy or whistling" when they had colds. In the large nonsilicot,ic group shown in table 'V.0 these rates were remark- ably constant as to age and years of employment and showed no ap- preciable trends with either factor. In the smaller group of employees with silicosis, the rates fluctuated slightly and were a trifle higher, but showed no age or length of employment trends. When the above question was worded to elicit a reply restricted to the presence of "wheezy and whistling" chest sounds at other times not associated with colds, the frequency of this symptom in both the nonsilicotic group and workers with silicosis was greatly reduced. In the nonsilicotic group, the prevalence of this symptom increased somewhat with age and also length of employment at metal mines, ranging from 5.6 percent in the youngest age group with short mining experience to 14.9 percent in the oldest group with the longest mining experience. In the smaller silicotic groups, the symptom was re- ported only somewhat more frequently in comparable age and em- ployment groupings (6.7 to 22.2 percent) and could not be calIed_ a prominent symptom: Complaints of a temporarily disabling chest illness within the past 3 years was fairly frequent and was reported by about 20 percent of most age and length of employment groups in the large nonsilicotic population. No trend was observed except that it occurred slightly more frequently in the groups under 45 years of age. In the silicosis groupings, chest illness was reported a little more frequently-with in- creasing age and length of employment, but there were surprisingly few differences between these groups and the groups of nonsilicotic miners. reath Shortness of Breath Shortness of breath is an uncommon complaint among healthy young adults, but is frequently observed among elderly persons, obese per- sons, and those with emphysema and heart disease. It is generally - considered a common manifestation of silicosis, especially in adv-anced stages when emphysema is a frequent complication. Questions re- garding shortness of breath were based on studies made by. British observers in their extensive research studies of coal miners pneumo- coniosis. - -_ : Table V.9 shows the frequency of complaints of some degree of shortness of breath by age and length of employment groupings. In the nonsilicotic population it was reported by less than 5 percent of the miners under 35 years of age, The prevalence of this complaint gradually increased with age and years of employment to about 20- percent in the older age groupings with long employment at metal mines. In the much smaller silicotic group, shortness of breath was 135 k

a much more common complaint in all age groups, ranging from an average rate of 16.3 percent for all men under 45 years of age and 21.7 percent for men 45 to 54 years of age to 36.8 percent for those of 55 years of age and over. Within these broad age groupings, there was no clear trend with length of employment, except that the highest rate, 38 percent, was found in the oldest group of men with 30 years or more of mining experience. Earlier studies have shown that many industriall workers with early or moderate degrees of silicosis did not experience any remarkable subjective complaints of the disease. Consequently, in evaluating the symptoms of silicosis, they should be related to other findings such as the degree of changes in the chest roentgenogram. Table V.10 and figure V.6 show the prevalence of shortness of breath with relation to the degree of silicosis and length of employment at the metal mines, and table V.11 shows shortness of breath related to the detailed X-ray categorization by age and also by years of employ- ment at metal mines. Table V.10 also shows that 1,141 out of 12,479 metall mine workers, or 9.1 percent, reported some degree of shortness of breath. Among the large population of 11,922 with no X-ray evidence of silicosis, the rates for this symptom increased from 5.8 percent to 20.4 percent with increasing years of mining employment. Among the rather small group of 133 workers with suspect or doubtful chest films, only 17, or 12.8 percent, reported this complaint. With simple silicosis, however, 71 of the 271 workers so classified, or 26.2 percent, reported shortness of breath, and the percentage rates increased from 15.6 for those with less than 15 years employment to 38.5 percent for those with 35 or more years of employment. With more advanced or complicated silicosis, the symptom was reported by 55 out of 153 employees, or 35.9 percent. The rates increased from about 25 percent for those employed less than 25 years to over 40 per- cent for those employed more than 25 years. Hence, it will be observed that shortness of breath was reported about three to four times as frequently among the silicotic as the nonsilicotic miners and ranged somewhat higher among those with complicated silicosis with in- creasing years of employment. Table V.11 shows the prevalence of shortness of breath reported according to the degree of change in the X-ray chest films as defined in the I.L.O. Radiological Classification of the Pneumoconioses, and ' also by broad qge and length of exposure groupings. The preva- lence of this symptom for alll negative chest films was 8.4 percent and increased regularly from 18.6 percent for all category 1 films to 50 percent for the 56 films classified as categories B and C denoting the more advanced complicated silicosis cases. A similar trend in the prevalence of shortness of breath within the broad age groupings was 136 TABLE V.10.-Shortness of breath among workers at 50 metal mines* according to lung field markings and years at metal mines Years at metal mines Lung field markings Total I -18 15-24 - 25-34 Number examined Total------------------ t12, 479 7,576 3,161 1,220 No abnormal markings_________ 11,922 7,503 2,973 1,015 Doubtful_____________________ 133 34 47 36 Simple silicosis________________ 271 32 98 102 Complicated silicosis-----______ 153 7 43 67 Number with shortness of breath Total------------------ 1, 141 444 373 203 No abnormal markings-_____-__ 998 432 331 147 Doubtful_____________________ 17 5 3 6 Simple silicosis________________ 71 5 28 23 Complicated silicosis___________ 55 2 11 27 Percent with shortness of breath j Total------------------ 9. 1 5.9 11.8 16.6 No abnormal markings_________ 8.4 5.8 11.1 14. 5 Doubtful--___-._______________ 12.8 14.7 6.4 16.7 Simple silicosis________________ 26.2 15.6 28.6 22.5 Complicated silicosis-__________ 35.9 28.6 25.6 40.3 ---- - - -_ _~ - •Excludes uranium mine workers. - j ' - - - - f Does not include 8 workers with no information on shortness of breath.. 522 431 16 39 36 121 20.4 18.8 38.5 41.7 - - - also observed by categories, and a somewhat less regular trend was shown by length of exposure groupings;. The question has been raised as to whether the responses to questions regarding shortness of breath show a relationship to the elevation at which men work and live. The percent of workers with slight and moderate shortness of breath reported is shown according to elevation of the mine and living area in table V 12. The 50 metal mines were separated into 3 groups by elevation. Consideration was given both to the elevation at the entrance of the mine and at the surrounding areas where the work.e_rs lived. Broad groupings were possible in which each_miAp-could be placed. Among the large group of men without silicosis working at less than 2,000 feet, slight shortness of breath was reported among 137

40 30 10 TABLE V.11.-Shortness of breath among workers at 50 metal mines* according to detailed lung field markings, age and years at metal mines . Lung field markings Total-------- No abnormal markings-------_- Doubtful----------- Category 1------_-- Category 2--------- Category 3--------_ Eggshell-----------_ Category A-__----_- Category B--------_ Category C--------- Number with shortness of breath 0 Under 15 7,537 39 ® 15-24 25-34 YEARS IN METAL MINES 35 and over 3,020 141 1,051 169 447 75 NUMBER EXAMINED Silicotic Nonsilicotic FIGURE V.6: Shortness of breath among workers with and without silicosis according to years worked in 50 metal mines. 5.3 percent, moderate shortness of breath among 0.5 percent for those men less than 45 years of age, and 12.6 percent and 3.5 percent for men 45 years of age and over. Workers at 2,000-4,999 feet and at 5,000 feet and over showed a slightly lower percentage with slight and with moderate shortness of breath among both age groups. Workers with silicosis 45 years of age and over had approximately double the percentage with slight shortness of breath and more than three times the percentage with moderate shortness of breath as among normal. workers. There was little difference in shortness of breath according to elevation. This may be partly accounted for by the fact that men working at higher elevations expected to have some degree of short- ness of breath and did not consider this abnormal when it was no worse than their fellow workers. 138 Total-------- No abnormal markings--------- Doubtful------_---- Category 1-----_--- Category 2--------- Category 3------_-- Eggshell------------ Category A-_------- Category B_----_--_ Category C--------- t12, 479 11,922 133 43 186 28 14 97 38 18 1,141 998 17 8 50 12 1 27 19 9 Age 7,760 7,681 30 8 26 1 1 12 1 426 416 2 4 4 3,182 2,934 64 22 87 15 5 31 14 10 398 341 9 5 25 4 4 5 5 1,537 1,307 39 13 73 12 8 54 24 7 317 241 6 3 21 8 1 19 14 4 Xe@rs_ at metal mines 10,737 10,476 81 21 92 13 4 37 I 7 6 817 763 8 5 25 3 -----7 3 3 Percent with shortness of breath Total_------- No abnormal markings--------_ Doubtful-__---_---- Category 1_-----_-- Category 2------__- Category 3_-------_ Eggshell------------ Category A--_---__- Category B___-_-_-- Category C---_----- 9. 1 8.4 12.8 18.6 26.9 42.9 7.1 27.8 50.0 50.0 5.5 12. 5 11.6 14.1 22.7 28.7 26.7 12. 9 35.7 50.0 20.6 18.4 15.4 23.1 28.8 66.7 **12. 5 35.2 58.3 **57. 1 •Excludes uranium mine workers. _ tDoes not include 8_workers with no data on shortness o(,breath. •*Based on less than 10 employees in exposure group. 7.6 7.3 9.9 23.8 27.2 23.1 18. 9 **42. 9 **50. 0 1,220 1,015 36 19 68 9 6 40 17 10 203 147 6 2 17 4 16 6 5 16.6 145 16.7 10.5 25.0 **44. 4 40. 0 35.3 50.0 522 431 16 3 26 6 4 20 14 2 121 88 3 1 8 5 1- 4 10 1 23.2- 20. 4 18.8 **33. 3 30.8 **83. 3 **25. 0 20.0 71.4 **50. 0 1n

TABLE V.12.-Shortness of breath among workers at 50 metal mines* according to elevation of mine and age, workers with or without silicosis Less than 45 years of age 45 years of age and over Short of breath Short of breath Elevation Number Percent Number Percent examined Num- examined Num- ber ber Slight I Moder- Slight Moder- ate ate Workers without silicosls Less than 2,000 feet__ 2,000-4,999 feet______ 5,000 feet and over___ 2, 056 2,484 3,174 120 118 180 5.3 4.3 4.8 0.5 .5 .9 1,527 1,319 1,501 246 145 206 12.6 9.0 10.8 3.5 2.0 2. 9 Workers with silicosis Less than 2,000 feet__ 2,000-4,999 feet______ 5,000 feet and over___ 1 28 20 ---2- 6 3.6 15.0 3.6 15.0 37 184 156 12 52 53 21.6 20.1 22.5 10. 8 8. 2 11.6 •Exciudes uranium mine workers. SILICOSIS RELATED TO TYPE AND DURATION OF EXPOSURE rears in Metal Mining As has been found in previous industrial studies of silicosis, the prevalence of silicosis increased rapidly with increasing years of work within the metal mining industry. Table V.13 shows the increasing rate off prevalence in increments of 5-year work exposures. The large mining population involved in this survey permits a 5-year breakdown into 10 groupings ranging from less than 5 years of exposure to 45 years and over. The following observations may be made from table V.13: 1. No cases occurred with less than 5 years of exposure. 2. Seven cases (0.2 percent) occurred in workers with 5-9 years of exposure. 3. After 10 years or more of exposure the prevalence rates rose rapidly in 5-year increments from 1.4, 3.0, 7.6, and 12.1 per- cent up to an average rate of 16.6 percent for the four ex- posure groups shown as working 30, 35, 40, and 45 years and over. The variation in the rates in these four longest work- ing groups is attributed to the smaller population at risk and the sizable proportion of older men in these groups working at mines offering relatively low free silica exposures. 140 Taking the chest X-ray film. Table V.13 also shows that the proportion of complicated to simple silicosis cases tended to increase in the groups with increasing duration of exposure: = Age of Workers.. - Although the miners' age and their years of employment in the metal mining industry have a close relationship, it is of interest to note the prevalence of silicosis in this mining population by age categories. Table V.14 and figure V.7 show the increasing prevalence of silicosis

TABLE V.13.-Number and percent of metal mine workers* with X-ray evidence of silicosis according to years at metal mines Silicosis-number Silicosis-percent Number Years at metal mines examined Total Simple Com- Total Simple Com- plicated pllcated Total------------- 14,076 476 305 171 3.4 2.2 1.2 Less than 5 years--------- 3,530 ------ ------ ------ ------ ------ ------ 5-9--------------------- 2,986 7 7 ------ .2 .2 ------ 10-14------------------- 2, 397 35 27 8 - . 4 1. 1 . 3 15-19------------------- 1, 927 58 - 47 - 11 3. 0 2. 4 . 6 20-24-------_----------_ 1, 416 107 69 38 7. 6 4. 9 2. 7 25-29------------------_ 709 86 50 36 - 2.1 7. 1 5.0 30-34------------------- 578 105 65 40 18.2 11.3 6.9 35-39------------------- 346 51 28 23 14.8 8.1 6.7 40-44------------------- 156 21 9 12 13.5 5.8 7.7 45 and over-------------- 31 6 3 3 19.4 9.7 9.7 •Includes uranium miners. TABLE V.14.-Number and percent of metal mine workers* with X-ray evidence of silicosis according to age Silicosis-number Silicosis-percent Number Age in years examined Total Simple Com- Total Simple Com- plicated plicated Total------------- 14,076 476 305 171 3.4 2.2 1.2 Less than 20------------- 155 ------ ------ ------ ------ ------ ------ 20-24------------------- 1,140 ------ ------ ------ ------ ------ ------ 25-29------------------- 1,652 ------ ------ ------ ------ ------ ------ 30-34------------------- 2,046 ------ ----- ------ ------ ------ ------ 35-39------------------- 1,951 7 5 2 . 4 . 3 . 1 40-44------------------- 2,042 50 38 12 2.4 1.9 . 5 45-49------------------- 1,912 81 53 28 4.2 2.8 1.4 50-54------------------- 1,550 134 94 40 8.6 6. 1 2.5 55-59------------------- 1,000 115 68 47 11.5 6.8 4.7 60-64------------------- 565 69 40 29 12.2 7.1 5. 1 65 and over-------------- 63 20 7 13 31.7 11. 1 20.6 •Includes uranium miners. with increasing age, in increments of 5 years, and ranging from less than 20 years of age to over 65 years of age. Silicosis was not observed in chest films of miners of less than 35 years of age, and only 7 cases or 0.4 percent were found among the 1,951 workers in the 35-39-year age grouping. Beginning with the 40-44-year age group with a prevalence rate of 2.4 percent, there was 35 30 25 20 10 5 0 Under 35 ® 35-39 40-44 45-49 50-54 55 59 60-64- 6 d ver_ AGE, years- ,: 4 993 1951 2,042 1,912 1,550 1,000 565 63 ~ ~ NUMBER EXAMINED ® Simple silicosis Q Complicated silicosis _ b`IGURE V.7.-Percent of all metal mine workers with silicosis by age. 143 ~ I 142 ( _ - P 707-103 0-64-11

a moderate increase in the rate for positive cases with each succeeding age group until it tended to level off at about 12 percent in the 55-59- and 60-64-year age groups. The 63 men examined who were in the 65-year-and-over age group included 20 cases of silicosis, or 31.7 per- cent. Of these 20 cases, 13 or two-thirds were classified as compli- cated silicosis. Age and Y'ears in Metal Mining Table V.15 and figure V.8 show the prevalence of silicosis both by 10-year age groupings and by the years of mining employment. Within the three oldest broad age groupings beginning with the age of 40-49 years, it will be seen that the prevalence rates for silicosis rose sharply within these age groups with increasing years of em- ployment, but in no instance quite reaching 20 percent. Ycars in Metal Mining and Principal Occupation It has been shown that there is a close correlation between the num- ber of years worked at metal mines and the prevalence of silicosis. It is of particular interest from the viewpoint of evaluating and controlling the silicosis problem to determine what occupations may have been largely responsible for causing the disease and their relative importance, in pointing out the need for further control measures in reducing the exposure to silicious dust. Table V.16 shows the prevalence of silicosis among the employees of 50 metal mines by years of employment at metal mines and by broad categories of principal occupation.* Of the 426 workers with silicosis, 344 or 80.8 percent had been employed principally under- ground, 62, or 14.5 percent had been employed on the surface, and 20 or 4.7 percent had no principal occupation. The overall prevalence rate for all 8,435 underground workers was 4.1 percent, and for the 2,870 surface workers, 2.2 percent. For underground workers, the prevalence rates ranged from 2.0 percent for transportation workers, 2.2 percent for maintenance and construction workers, 3.9 percent for miscellaneous workers, and up to 5.0 percent for the large group of faceworkers. For surface workers, the prevalence rates for silicosis ranged from less than 1 percent (0.7) for both transportation workers and miscel= laneous workers up to 3.5 percent for millworkers at the dustiest surface operation. *Principal occupation refers to work performed during more than half the time spent in metal mining, except miners working 10 years or more at the face are classified as faceworkers. TABLE V.15.-Number and percent of metal mine workers* with X-ray evidence of silicoszs according to age and years at metal mines.. - Age in years Total Less than 10 years Years at metal mines 20-29 30-39 40 years years years J and over 10-19 years Total examined Total---------- 14,076 6,516 4,324 2,125 924 187 Less than 20--------- 20-29--------------- 155 2,792 155 2,714 -----78- 30-39--------------- 3,997 2,284 1, 671 42 40-49--------------- 3,954 999 1,778 1,126 51 50-59--------------- 2,550 325 696 801 667 61 60 or over------------ 628 39 101 156 206 126 Number with silicosls Total---------- 476 7 93 193 156 27 Less than 20--------- 20-29--------------- ------ - ------ - 30-39---------=----- 7 ------ - 6 i - ------ 40-49--------------- 131 4 42 77 $ 50-59--------------- 249 3 40 95 107 4 60 or over------------ 89 5 20 41 23 Percent with sillcosls Total---------- 3.4 0.1 2.2 9.1 16.9 14. 4 Less than 20--------- 20-29--------------- 30-39--------------- .2 ------ - .4 2. 4 40-49--------------- 3.3 4 2.4 6.8 15.7 50-59--------------- 9.8 .9 5.7 11.9 16.0 6.6 60 or over------------ 14.2 5.0 12.8 19.9 18.3 'Includes uranium miners. By far the most important group of occupations with reference to the silicosis problem are those included in the category "face- workers," who were engaged in mining production and development operations. Silicosis occurred in 267 or 5.0 percent of the 5,330 face- workers. These 267 cases comprised 62.5 percent or well over half of the 426 cases of silicosis found among the 12,487 workers at these 50 metal mines. Among the 5,330 faceworkers, silicosis began ap- pearing after 10 years of employment and increased to 10.7 percent 144 1 145

.~ o c' ~• m~, m co a~ CD 0 ° 0 ° 5 m M CD ~ • m CD c'+ CD CD ID CD m U) C m ~ ~ ~ ~ m .h f-+ QQ ~• ~„ rt ~, (D P N ~ (b FF+ H. «~ m SD J ^ G o m a m Q Q [R P ,. f•la M ~ v ~ ~ fn N ~ f~ ~ CD ~ UQ ? 0 o O . ~ ~ O O 4 O ~ 2 ~ m ~ ~ 5 rh d m m P m ¢ . r- m o !r ~ ~ UZ • i:;:'~ ~ CD K ,..~ ~ C4 ~ w'' O s ~ rr O UR 0 ~ (D n ~ ~ P n ~-~r ~ S ~ ~ SZ ~ m p ~ CD m ~ c~ ~ ~ m ~ P• .~ ':'S O . ~. o ........ y~ ~c o +d'. ~ v7 N 0 . V ? y ~ y ti. a J ~ N J tp 0 ~ W Q ~. O +:?~;c;:i.. :i~:._...__._.:........ .......... ___--_ tn OD W N P f s ~ 4 J . 9 ~ N V7 ~ F A V Q ~.. / y O . F _ ~ .9 <.: 9 ! d / 0L~ \~ ^ TABLE V.16.-Percent of workers with evidence of silicosis at 50 metal mines* according to principal occupation and years at metal mines Total Less than 10 years 10-19 years 20-29 years 30 years and over Principal occupation Number P Number Per- Number Per- Number Per- Number Per- Exam- Sili- er- cent Exam- Sili- cent Exam- SilI- cent Exam- Sili- cent Exam- Sili- cent ined cosis ined oosis ined cesis ined cosis ined cosis Total_________________ 12,487 426 3.4 5,411 7 0.1 3,983 82 2.1 2,016 163 8.1 1,077 174 16.2 Underground total_____ 8,435 344 4.1 3,547 4 . 1 2,802 65 2.3 1,381 132 9.6 705 143 20.3 Face_______________________ 5,330 267 5.0 2,089 2 . 1 1,874 47 2.5 904 97 10.7 463 121 26.1 Transportation______________ 1,265 '25 2.0 612 ____ _____ 394 7 1•8 176 9 5.1 83 9 10.8 Maintenance and construction_ 1,171 26 2.2 569 2 . 4 348 9 2,6 173 11 6.4 81 4 4. 9 Miscellaneous_______________ 669 26 3.9 277 ____ _____ 186 2 1. 1 128 15 11.7 78 9 11.5 Surface total__________ 2,870 62 2.2 1,148 3 . 3 915 14 1.5 488 25 5.1 319 20 6.3 Transportation______________ 307 2 . 7 116 _ _____ 113 1 . 9 50 1 2.0 28 __-__ _____ Maintenance and construction _ 1,074 28 2.6 392 ____ _____ 342 2 . 6 192 14 7.3 148 12 8.1 _______________________ Mill 777 27 3.5 370 3 . 8 253 10 4.0 106 9 8.5 48 5 10.4 _ Miscellaneous_______________ 712 5 . 7 270 207 1 . 5 140 1 . 7 95 3 3.2 No principal__________ 1, 182 20 1. 7 716 _ _ 266 3 1. 1 147 6 4. 1 53 11 20. 8 •Ezdudes uranium mine workers. r .? v . i ~ I I i

TABLE V.17: Silicosis among metal mine workers* by principal occupa.tion and years at metal mines Underground Surface Years at metal mines Total No prin- Transpor- Mainte- Miscel- Transpor- Mainte- Miscel- cipal Face tation nance and laneous tation nance and Mill laneous construction construction Number examined Total----------------------- 10,286 4,379 1, 109 900 555 263 865 641 513 1,061 0-5------------------------------- 2,423 714 305 238 133 41 146 193 104 549 5-9------------------------------- 2,347 1,063 268 225 96 65 201 166 124 139 10-14----------------------------- 1,884 934 182 145 79 55 171 107 81 130 15-19----------------------------- 1,304 579 151 121 71 42 111 81 59 89 20-24----------------------------- 1,027 490 95 78 73 25 86 46 58 76 25-29----------------------------- 563 255 54 41 39 15 58 27 35 39 30-34----------------------------- 444 218 35 32 42 9 45 13 26 24 35 and over----------------------- 294 126 19 20 22 11 47 8 26 15 Number with silicosis Total----------------------- 415 260 25 25 26 2 27 ~ 27 5 18 0-5--------------- ---------------- ------ - ------ - ------ - 5-9------------------------------- 7 2 2 ------ - 3 -------- 10-14----------------------------- 31 19 2 3 i 1 ------ - 4 1 15-19----------------------------- 49 27 5 5 1 2 6 1 2 20-24----------------------------- 91 60 3 6 5 8 7 2 25-29----------------------------- 70 36 6 5 10 1 6 2 1 3 30-34----------------------------- 95 67 4 1 6 6 3 2 6 35 and over----------------------- 72 49 5 3 3 5 2 1 4 Percent with silicosis Total----------------------- 4.0 5.9 2.3 2.8 4.7 0.8 3.1 4.2 1.0 1.7 D-5------------------------------- -------- 3 ----- - 2 -------- --- -------- • 9 -------- - -------- -------- -------- 1.8 ------- -------- -------- i-9 - - t0-14 ------------ . 1.6 . 2.0 ---- 1.1 2.1 1.3 1.8 -------- 3.7 -------- ----------------- 3 8 4 7 3.3 4.1 1.4 ----- 1.8 7.4 1.7 t5-19----------------------------- . 8 9 . 2 12 3.2 7.7 6.9 ------- - .3 15.2 ------- 20-24----------------------------- . 12 4 . 14 1 11. 1 12.2 25.6 - 6.7 - 0. 3 7. 4 2. 9 Z5-2y- -------------------------- . 21 4 . 30 7 11.4 3.1 14.3 ------_ - 13.3 23.1 7.7 30-34----------------------------- . 24 5 . 38 9 26. 3 15. 0 13. 6 -------- 10.6 25.0 3.8 35 and over----------------------- . . sFxnlpdes uranium mines and 7 iron and lead-zinc mines in low free silica limestone formations. Ill~~~;.l,s~l,lll"I'1!IiU" lll „lii,~llhl'Br!~' ,iP,~~ ~~Ili!~y,~,;14!,IlVnpql~IC~'Ib~'ll',9BI~ ~lltpa.i'I'~~I~!iql~lll:~'~'I'I'llbilll9~~I~NY'~!~it ~'j il'tN;lll~'~4hVlI'I'~I~h~ll'~III!"'llC~'IC'i ~'f~~l 91la~ilb"19'IC IIG'~ I ',~INP~~~!1h1IhP~';;JIll9~1i ''i'31wi1

Present Occupation • Table V.18 shows in detail the present occupation of all workers and of workers with silicosis. From this table it was possible to learn the number of workers engaged in a variety of occupations at the mines studied at the time of the medical examinations. Thus, among the 4,474 men who were working at the face, 3,066 were stope miners, 686 were drift miners, 449 were raise miners, and 273 were performing other work at the face. Underground transportation consisted chiefly of motor crews but there were also 265 underground hoisting operators, 177 skip tenders and chute pullers, 94 mobile equipment operators, and 32 grizzlymen. The two principal groups of under- ground maintenance and construction workers were timbermen and mechanics and pipemen. Miscellaneous underground workers were primarily supervisors and engineers. A classification of'workers by present occupation tells only what a man was doing at the time he was examined and does not indicate how long he had been engaged in that particular job. However, it is of interest to observe where persons with silicosis were found at the time they were examined. There were 269 persons with simple or complicated silicosis who were presently employed underground and 98 of these were working at the face. On the surface, there were found to be 157 persons with silicosis. The great majority of these had previously had years of underground working exposure. Present Occupation Compared With Principal Occupation Table V.19 shows the present occupation of metal mine workers and indicates the principal occupation which each had followed during his entire mining experience. For example, among 4,474 men now work- ing at the face, 3,883 had worked principally at that occupation, 161 men had spent most time in underground transportation, 52 had been chiefly in underground maintenance and construction, 72 had been in other underground work, 41 had worked on the surface, and 265 had not worked at any one job long enough to have a principal occupation. Although the largest group of workers was found under the same classification for principal as for present occupation, there were many other types of work formerly followed by substantial groups of persons. The practice of transferring older and less physically fit workers from underground to surface jobs was reflected in the figures showing percent with silicosis by present and principal occupation. The highest silicosis rates for men whose principal occupation had been at the working face were found in men presently working on the surface, namely 22.1 percent with silicosis in maintenance and con- struction, 23.2 percent in surface millwork, and 21.0 percent at other TABLE V.18.-Workers at 50 metal mines* according to occupation at time of medical examination Preaent occupation Number of workers Number with eillcoeis Grand total--------------------------------------- 12, 487 426 Underground-face-total----- - - - ------ - ----------- 4,474 98 Stope miner-------------------------------------------- 3,066 57 Drift miner-------------------------------------------- 686 22 Raise miner-------------------------------------------- 449 5 Otherfaceworkers-------------------------------------- 273 14 Underground-transportation-total__ _ ____ ____ _ ____ 1,468 33 Motor crew-------------------------------------------- 900 17 Grizzlyman-------------------------------------------- 32 Underground hoisting operator---------------------------, 265 12 Skip tender and chute puller----------------------------- 177 3 Mobile equipment operator_________________---t--------- 94 1 Underground-maintenance and construction-total__ 1,818 75 Timberman-------------------------------------------- 505 38 Trackman--------------------------------------------- 148 3 Electrician ------- ----------------------------------- 185 4 -- Mechanic and pipeman---------------------------------- 492 11 Other maintenance and construction workers--------------- 488 19 Underground-miscellaneous-total_ ___ _ ___ _ _ _ _ _ _ _ _ _ 1,078 63 Supervisor--------------------------------------------- 535 46 Powderman-------------------------------------------- 43 5 Nipper------------------------------------------------ 60 2 Engineer and eampler___________________________________ 201 4 Generallaborer--------------------------------- ------- 239 6 Surface-tranaportation-total---- - - - - - - - - ---------- 424 8 Hoiatman--------------------------------------------- - 144 3 Topman --------------------------------------------- 41 -------- - Mobile equipment operator------------------------------ 239 5 Surface-maintenance and construction-total-_---___ 1,404 67 Electrican ------------------------------------------- 181 2 -- Mechanic and pipeman---------------------------------- 448 15 Carpenter------°------------------------------------- 126 11 Bitrepairman------------------------------------------ 19 1 welder------------------------------------------------ 136 2 Generallaborer----------- ------------------------------ 494 36 Surface-mill-total------------------------------- 898 38 Crusher worker----------------------------------------- 314 10 Other millworkers-------------------------------------- 584 28 Surface-miscellaneous-total---------------------- 923 44 Office and generalsupervision---------------------------- 566 13 Assayer --------------------------------------------- 110 2 --- Miscellaneous laborer----------------------------------- 247 29 •E:c]udes uranium mine workers. 152 1 153

TABLE V.19. Present occupation compared with principal occupation of workers at 50 metal ntines* according to percent with silicosis Present occupation Principal occupation Under ground Surface Face Transpor- tation Maintenance and construction Other Transpor- tation Maintenance and construction Mill Other Number examined Total-------------------------------- 4,474 1, 468 1, 818 1, 078 424 1, 404 898 923 Underground total____________________ 4, 168 1, 257 1, 486 876 89 284 77 198 Face-------------------------------------- 3, 883 326 456 335 42 145 43 100 Transportation_____________________________ 161 858 113 37 33 33 9 21 Maintenance and construction________________ 52 52 890 47 11 96 5 18 Other------------------------------------- 72 21 27 457 3 10 20 59 Surfacetotal------------------------- 41 54 120 59 282 977 706 631 Transportation_____________________________ 9 15 9 1 240 18 8 7 Maintenance and construction________________ 9 14 68 14 19 863 38 49 Mill--------------------------------------- 15 16 12 10 10 39 628 47 Other------------------------------------- 8 9 31 34 13 57 32 528 No principal_________________________ 265 157 212 143 53 143 115 94 Peroent with siiicosis ----------------------- - Total 2 2. 2. 3 4. 1 5. 8 1. 9 4.8 4. 2 4. 8 ----- Underground total____________________ 2. 3 2. 5 4. 8 6• 8 4. 5 13. 0 14. 3 16. 2 4 2 5 2 11.2 11.9 7.1 22.1 23.2 21.0 F~ -__ ____ Transportation__ -------------------------- . .6 . 1.4 2.7 2.7 3.0 12.1 ________ 14.3 Maintenance and construction__________ ------ 1 . 9 2.0 6.4 __________ 1.0 --______ 16. Other ------------------- - 4.2 4.8 ---------- 3.5 ---------- ---------- 5.0 8. 5 _ -- 1 7 1.1 2.6 3.8 1. 0 Surface total------------------------- --- ---------- . ---------- -------- Transportation ------------------------- i -------- ---------- ---------- ---------- -------- 7• 1 ---------- 2. 7 on--------- construct ------- -- - ---------- -- 5.1 Mill ---------------------------- - - - -- - -------- 7.7 --------- ---------------------- Other---- -- --- No principal------------------------- ------ . 4 - - 1.3 1. 4. - 1.4 1.9 3. 5 -- •Ezcludes workers in uranium 7mines.' I I'VI I I' I I ~, 11 i I I ;I',ul I f.1

surface operations. Workers whose present and principal occupa- tion was at the face had a silicosis rate of only 2.4 percent. Most of these had worked only a short time. The highest silicosis rates for men with principal occupation of underground transportation, underground maintenance and construction, and other underground work were found among men now engaged at other surface work. There was very little silicosis among men with present and principal occupation in surface work and no long experience underground. Geographical Location As might be expected, the great majority of the 50 metal mines studied were located in the Western States. Mines in this region were placed in two groups, namely the Northwest, comprising the States of Idaho, Montana, Washington and Wyoming, and the Southwest comprising Arizona, California, Colorado, Nevada, New Mexico, and Utah. Crude silicosis prevalence rates were compared for these two regions with the following results for the Northwest and Southwest, respectively : total silicosis 4.4 and 4.4 percent, simple silicosis 2.9 and 2.8 percent, complicated silicosis 1.5 and 1.6 percent, and doubtful silicosis 0.9 and 0.8 percent. Considering the great difference in op- erating conditions for individual mines it was surprising that the combined data for the 17 Northwest mines and the 17 Southwest mines should yield such uniform silicosis prevalence rates. The remainder of the country east of the Rocky Mountains was divided into three areas according to a rough estimate of the percent of free silica in the mine environment. Silicosis prevalence in areas of relatively high, moderate and low silica was as follows : total silicosis, 4.3 percent, 1.6 percent, and 0.7 percent, respectively; sim- ple silicosis, 1.6, 1.2, and 0.6 percent; complicated silicosis, 2.7, 0.4, and 0.1 percent. Silicosis in the region with relatively high free silica was comparable to the prevalence in the Western States, but there was a sharply reduced rate in the other two geographical areas. Silicosis According to Commodity Produced Table V.20 and figure V.10 show the percent of workers with silicosis according to commodity produced. It appears that silica content of the dust was much more important than the type of. commodity produced in &ffecting the crude silicosis rate. Excluding the iron and lead-zinc mines with low free silica exposures, the total crude rates for silicosis were much the same, namely : iron mines 4.2 percent, lead-zinc mines 4.8 percent, copper mines 3.6 percent, uranium mines 3.1 percent, and mines for all other commodities 3.7 percent. In the iron mines with low free silica exposures, silicosis 156 TABLE V.20.-Silicosis among metal mine workers* according to commodity produced, by years at metal mines Mine commodity Total Number of years at metal mines -10 6,516 Total examined Total---------°------- &on------------------------- Lead-zinc-------------------- Copper----------------------- Uranium--------------------- Other--------°-------------- Iront------------------------ Lead-zinct------------------- Total------------------ Iron------------------------- Lead-zinc--------------------- Copper------------------------ Uranium--------------------- Other------------------------ Iront------------------------ Lead-zinct------------------- Total------------------ Iron----------------------- Lead-zinc--------------------- Copper----------------------- Uranium--------------------- Other-------------------- ---- Iront----------°------------ Lead-zinct-------------------- 14, 076 1,112 2,622 4,010 1,589 2,542 962 1,239 476 47 127 146 50 95 3 8 3.4 4.2 4:8 3.6 3.1 3.7 .3 .6 •Includesuraniummineworkers. - tIncludes mines in low free silica limestone formations. 375 1,183 1,538 1,105 1,674 546 95 10-19 4,324 395 871 1,381 341 541 239 556 Number with slilcosis 7 93 10 ; 27 21 11 22 1 1 20-29 2,125 227 395 748 109 220 137 289 193 12 50 58 30 41 1 1 3oandover 1,111 115 173 343 34 107 40 299 183 Percent witb slltcosis 0.1 2.2 2.5 3.1 1.5 3.2 4.1 .4 .2 9.1 5.3 12.7 7.8 27.5 18.6 .7 .4 24 ; 48 66 9 29 1 6 16.5 20.9 27.7 19.2± 26.5 27.1 2.5 2.0 157 1

\\\\\O~~ \\\\\\\\\\\\\\\\\\\\\\\~ M N 1 0 1 O 1 Ln M ~ M J O ~ ~ ~o V 0 y~pn ~ ~ O U '~ Y Y ='° a ~ d M b ~ ~ o v c~ W 0 [> Z N ~ Q N E y ~ U 'm B A ~ ¢ ~ ? ~ V.a N H ~ g 0 N ®~ g ~ y "ro was found in 0.3 percent and in low free silica lead-zinc mines in 0.6 percent. In no group of mines did persons with less than 10 years of ex- perience show as much as 1 percent with silicosis. In the 10-19-year experience group (again excluding low free silica mines) the percent with silicosis was as follows : copper 1.5 percent, iron 2.5 percent, lead-zinc 3.1 percent, uranium 3.2 percent, and other commodities 4.1 percent. In the 20-29-year experience group, iron mines with 5.3 percent and copper with 7.8 percent were more favorable with respect to silicosis than were lead-zinc with 12.7 percent, other com- modities with 18.6 percent, or uranium with 27.5 percent. The longest exposure groups, 30 years and over, showed iron and copper mines with about the same percent of silicosis. Lead-zinc, uranium, and other commodities had a higher silicosis rate. At mines with low free silica, silicosis was minimal even at the longest duration of exposure, with 2.5 percent for iron mines and 2.0 percent for lead-zinc mines. Workers With Experience at One Mine Only and at Two or More Mines Table V.21 and figure V.11 compare silicosis prevalence for persons with experience at one metal mine only and for persons _who had worked at two or more mines. Men with employment at a single mine had the more favorable silicosis experience among almost all age groups of faceworkers, other underground workers, and surface workers, no matter what had been their length of service at metal mines. The one notable exception was. the higher silicosis rate among faceworkers with 30 years or more of experience at one mine. Em- ployment at several different mines apparently led to a more unfavor- able dust exposure and consequently to a greater prevalence and earlier appearance of silicosis. = - The rate of silicosis according to the number of years worked at metal mines for faceworkers who had worked at only one mine in- creased rapidly from 1.7 percent with 10-14 years of experience to 44.1 percent with 30 years and over. Faceworkers with experience at two or more mines showed a generally higher silicosis rate which rose with years of work from 2.6 percent to 27.0 percent. Other underground workers and surface workers did not show as rapid an increase in silicosis prevalence with increasing years at metal mines. Even after 30 or more years at metal mines, silicosis did not affect as much as 15 percent of these workers, whether they had ex- perience at one or more than one mine. 159 707-103 0-64-12

TABLE V.21.-Silicosis among metal mine workers* with experience of 10 years 45 or more at one mine only and at 2 or more mines by principal occupation and years at metal mines 40 FACE WORKERS Number examined Number with silicosis Percent with silicosis Years at metal mines At1 At 2 or At 1 At2or At1 At 2 or 35 mine only more mines mine only more mines mine only more mines Total-all occupationst 30 Total__________ 10-14--------°----- 15-19--------------- 20-24_______________ 25-29--------------- 30 and over__________ Total__________ 10-14--------------- 15-19--------------- 20-24--------------- 25-29--------------- 30 and over__________ Total__________ 10-14--------------- 15-19--------------- 20-24--------------- 25-29--------------- 30 and over__________ Total__________ 10-14--------------- 15-19--------------- 20-24--------------- 25-29--------------- 30 and over__________ 3, 310 2,199 201 207 6.1 9.4 1, 304 577 19 12 1.5 2.1 761 542 21 28 2.8 5.2 543 484 37 54 6.8 11.2 286 274 29 40 10.1 14.6 416 322 95 73 22.8 22.7 Face workers 1, 293 1,304 113 145 8.7 11. 1 586 345 10 9 1.7 2.6 261 317 6 21 2.3 6.6 199 293 21 39 10.6 13.3 104 149 13 22 12.5 14.8 143 200 63 54 44.1 27.0 Other underground workers 921 375 41 33 4.5 8.8 314 92 3 3 1.0 3.3 248 95 8 3 3.2 3.2 160 84 5 9 3.1 10.7 84 50 11 10 13.1 20.0 115 54 14 8 12.2 118 Surface workers 911 332 38 20 4.2 6.0 343 71 5 0 1.5 207 86 6 3 2.9 3.5 144 71 10 5 6.9 7:0 78 57 4 6 5.1 10.5 139 47 13 6 9.4 12.8 •Excludes uranium mines and 7 iron and lead-zinc mines in low tree silica limestone formations. tlncludes no principal occupation. z 25 w U ~ ~ 20 15 10 5 20 15 H z w IC-21 10 LU (L 5 25-29 30 and over YEARS IN METAL MINES 586 345 261 317 199 293 104 149 143 200 NUMBER EXAMINED 10-14 15-19 20-24 l1Ld:~ CL~~h;:;: OTHER UNDERGROUND WORKERS I 30 and over 314 92 248 95 160 84 84 50 115 54 NUMBER EXAMINED ® One mine only Q Two or more mines 10-14 15-19 20-24 25-29 YEARS IN METAL MINES FIGURE V.11.-Silicosis among metal mine workers with exposure of 10 years or more in one mine only, and in two or more mines. (Excludes seven Iron and lead-zinc mines in low free silica limestone formations.) 160 ~ - 161

Silicosis Among Workers Excluded Because of Other Dusty Work There were 671 metal mine employees excluded from the discussion because they had previously worked in other dusty employment which might be capable of producing silicosis. Table V.22 shows the expe- rience of this group of workers compared with that of all metal mine workers in the study group. Workers with other dusty experieuce had about the same prevalence of silicosis as all metal mine workers when years in all kinds of dusty work were the same. For example, the former group with 30 or more years of dusty experience had 15.2 percent with silicosis compared with 16.5 percent for the latter group; for 10 to 19 years of experience the percentage with silicosis was 2.5 and 2.3 percent, respectively. Types of dusty employment included coal mining, tunnel work, smelting, foundry work, quarrying, and the mining of various non- metallic minerals. Approximately one-half of these men had spent from 5 to 10 years in other dusty work before entering metal mining employment. The remainder had spent 10 or more years in other dusty work. Therefore, it appeared that the exclusion of 671 metal mine em- ployees having had other dusty exposure from the mining population under study did not appreciably change the overall prevalence of silicosis in the study, when total years of exposure are taken into consideration. TABLE V.22.-Silicosis among metal mine workers with exposure in other dusty trades of 5 years or over according to total years in all dusty work Number with siiicosis Percent with silicosis Total years at• all dusty Total work number Workers All metal examined Total Simple Compli- with other mine cated dusty workerst experience Lesa than 10--------- 68 0 0 0 -------- 0.2 10-14--------------- 130 1 1 0 0.8 1.5 15-19--------------- 146 6 5 1 4.1 3.0 20-24--------------- 121 12 10 2 9.9 7.6 25-29--------------- 101 10 6 4 10.0 12. 1 30-34--------------- 61 9 6 3 14.8 18.2 35 and over---------- 44 7 3 4 15.9 116 'Includes total years spent in metal mining and all other dusty work. tIncludes workers at 50 metal mines and uranium mines excluding those with work in other dusty trades of 5 years or over. Silicosis by Periods of Work Experience Before and After 1935 Metal mine employees were divided into two groups according to the period of their work experience, namely, persons who had worked at metal mines at some time before 1935 and had experience in some or all of the intervening years since then, and persons whose only__ work experience had been.. in 1935 or later. It is obvious that perso_ris in the first group also must have worked orked in the second, since only employed miners were examined. = Table V.23 and figure V.12 show silicosis rates, specific for years at metal mines, for persons with experience beginning in each period. This permits some comparison of silicosis prevalence rates among workers in this study who had substantial exposure before dust con- trol measures became widely used and those employed only during the subsequent 25 years or so. When the group of 43 mines, exclud- ing those in low free silica limestone formations, was studied it was found that, among the relatively small group of workers with some mining experience before 1935 but who had worked at metal mines a total of only 10-14 years, the silicosis rate was 6.1 percent; a group of 1,818 persons who had worked the same number of years but only in 1935 or later had a rate of 1.5 percent. Corresponding figures for persons with 15-19 years at metal mines showed 8.3 and 3.3 per- cent with silicosis, respectively. After 20-24 years i_n_ metal_ mining, men with experience prior to 1935 had a silicosis prevalence of 12.7 percent compared with 7.2 percent for men with experience during Tor after.1935. _ In mines which were located in low free silica limestone formations there was no silicosis among the 1,066 men who had worked 10-24 years, including some time before 1935. For the earlierperiod (be- fore 1935), there was one case of silicosis after 25-29 years, four cases or 3.6 percent after 30-34 years, and three cases or, 1.3 percent after 35 years or more. For the later period, those persons who had worked in 1935 or subsequently, there were only 3 cases of silicosis among 1,745 men. For any one duration the affected group did not reach 0.5 percent. The trends shown in figure V.12 appear to indicate that although the prevalence of silicosis is substantially lower among men who began mining in 1935 or later than among those who worked before 1935, there continues to be a regular increase in prevalence with increasing years of experience in metal mining. In the more recent period the onset of silicosis was several years later than for persons with similar length of experience who had worked at some time before 1935. The curves for persons working in each period are of essentially the same shape suggesting that in recent years silicosis has been developing at a considerably slower pace than formerly, but that cases were still occurring. 162 1 163

TABLE V.23.-Silicosis among workers at metal mines* by period of work experience and total years worked at metal mines Number with work experience Percent with siiicosis Total At some time before Only since 1935 or Worked Worked Years at metal mines number 1935 as well as later later at some only examined time since before 1935 Number Number Number Number 1936 as or examined with examined with well as later silicosis silicosis later 43 metal mines Total_ _ __ _ 10, 286 1,765 290 8,521 125 0-5------------- 2,423 2 0 2,421 0 5-9------------- 2,347 24 0 2,323 7 0.3 10-14___________ 1,884 66 4 1,818 27 1.5 15-19___________ 1,304 120 10 1,184 39 8.3 3.3 20-24------------ 1,027 307 39 720 52 12.7 7.2 25-29___________ 563 508 70 55 0 13.8 30-34___________ 444 444 95 0 0 21.4 35 and over______ 294 294 72 0 0 24.5 Total_____ 7 iron and lead-zinc mines in low free silica limestone formations 2,201 456 8 1,745 3 415 0 0 415 0 226 0 0 226 0 285 2 0 283 1 0.4 510 10 0 500 1 .2 323 40 0 283 1 .4 103 65 1 38 0 1.5 111 111 4 0 0 3.6 228 228 3 0 0 1.3 •Excludes uranium mine workers. COMPARISON OF PRESENT WITH PAST STUDIES In evaluating data from silicosis studies it must be kept in mind that, except in cases of massive exposure to high silica bearing dust, it requires a number of years, sometimes 20 years and over, of exposure to the dust before evidence of the disease exists on chest roentgeno- grams. The positive chest film is the evidence of excessive dust ex- posure over the past several years and not necessarily the concentration existing during the survey. Because of this long latent period, in cases where excessive atmospheric dust levels have been 164 1 165

lowered, it may take a number of years before attending lower sili- cosis prevalence rates show up in subsequent chest roentgenographic surveys. In reviewing the past studies of silicosis in the metal mines of this country, the above factor seems quite evident. In the very early studies before dust control measures were used appreciably, miners were exposed to massive dust concentrations. Within a relatively few years of exposure this resulted in a high prevalence of advanced silicosis accompanied also by a high prevalence of tuberculosis among the silicotics. In general, great advances have been made by the metal mining industry in controlling dust, especially since around 1935. This would not show up in an immediate lower prevalence of silicosis, however, because of the reservoir of miners exposed to dust prior to this period. It probably would not have its full impact until 20 to 30 years later. The only valid criterion of adequate dust control measures is the absence of new cases of silicosis developing in men whose only exposure is subsequent to the installation of dust control measures. Fortunately the 1939 study of Non-Ferrous Metal Mine Workers in Utah presents considerable data which may be contrasted with data developed in 12 lead-zinc mines of the 1958-61 survey having similar characteristics. Approximately the same average percentage of free silica, 30 percent, was present in the settled dust samples of each group of mines. Table V.24 shows the prevalence of silicosis in the western lead-zinc mine workers examined in 1958-61 compared with Utah metal mine workers examined in 1939 according to years in metal mines. Table V.25 shows the weighted average dust levels at reasonably comparable selected operations during the same two sur- veys. The trend is favorable in that the prevalence of silicosis for lead-zinc mines in the 1958-61 survey was found to be approximately 40 percent lower than that found in the Utah 1939 survey. Even more striking is the 80 percent reduction in silicosis prevalence in the group employed in the mines less than 10 years and 72.8 percent reduc- tion for the group employed 10-19 years. When consideration is limited to faceworkers only, there is an even greater decrease from the silicosis prevalence observed in the 1939 survey. The reduction amounts to 81.3 percent for the group employed in metal mines less than 10 years and 76.5 percent for the group with 10-19 years of em- ployment. These groups are the best indicators of a reduction in ex- posure to dust during this interval of time. The environmental data of the 1958-61 survey shows a very favorable trend in reduction from the atmospheric dust levels found in the Utah 1939 survey. On the basis of median dust count values for lead-zinc mines in the 1958- 61 survey, there was a 53 percent reduction in dust concentrations at dry crushing and 78 to 90 percent reduction in dust counts at other areas where comparisons could be made. 166 ~ ~. - . ... .__. . _ i TABLE _V.24.-Silicosis in western lead-zinc ;mine workers examin_ecLin 1958-61 compared with Utah metal mine. workers examined in 1989 according to years at metal mines _ Years at metal mines All si Number exam- licosis Simple silicosis Co mp ailic licated osis ined Number Percent Number Percent Num ber Percent 1939 study Total_______________ 727 66 9.1 52 7.2 1 4 1.9 Less than 10 years--________ 394 4 1.0 4 1.0 0 0 10-19 years---------------- 228 30 13.2 26 11.4 4 1.8 20 years and over----______ 105 32 30.5 22 21.0 1 0 9.5 1958-81 study Total_______________ 2, 173 117 5.4 74 3.4 4 3 2.0 Less than 10 years-______-__ 10-19 years________________ 959 717 2 26 .2 3.6 2 17 .2 2.4 ---- 9- ---1. 2 20 years and over__________ 497 89 17.9 55 11.1 3 4 6.8 TABLE V.25.-Weighted average dust concentrations (mppcf) at comparable occu- pations in 12 lead-zinc mines studied in 1958-61 compared with Utah metal mines studied in 1939 Occupation Low 1939 study- average Median 1958-61 study Range High Underground Miner-------------------°-------- Motorman________________________ H oistman------------------------- Timberman_______________________ Surface Hoistman------------------------- Topman------------------------- Crusher-------------------------- Assayer---- ---------------------- 23.1 10.5 7.5 18.9 3.8 9.4 14.3 57.9 3.1 2.3 1.6 1.9 .6 1.1 6.8 6.5 1.3 1.5 1.0 .7 .5 .8 2.1 2.3 17.6 10.7 2.6 10.6 2.3 2.8 17.3 33.8 •1939 figures represent the average weighted average dust exposure for each occupati on. 167

As pointed out earlier, due to the long periods of exposure necessary to produce silicosis, prevalence data at any one time represents the collective exposure of that group over the past several years. Thus the prevalence data on silicosis in the 1958-61 survey in most instances would represent exposures during the previous 20 years or more. Without carefully collected and recorded environmental data on a periodic basis over the period of exposure, it is not possible with vali- dity to assign weighted levels of dust exposure to the workers. Such unfortunately is the case for the 1958-61 survey. Only in a very few cases do the environmental findings of the survey apply retrospectively more than a few years. It will be another 10-20 years before the full impact of the environmental levels of dust exposure found in the 1958-61 survey reveal themselves in correlative silicosis prevalence data. During this interval routine dust control monitoring and medical surveillance should be practiced to assure proper operation and maintenance of dust control procedures and the prevention of new cases of silicosis. Case Histories i i

FIGURE V.13.-Simple silicosis. Lead-zinc mine worker, white male, age 58, height 68 inches, weight 127 pounds. Occupational history: Surface laborer 3 years and welder 8 years ; flotation mill operator 21 years ; also motor operator in lead smelter 9 years. Medical history: Metal fume fever while welding in 1953-1-day duration. Moderate shortness of breath was only complaint. X-ray chest frlm: Lung field markings classified in "suspect" category. Classi- cal eggshell ealcifications, some pleural abnormalities, and left apical bullae. • Diagnosis: Simple silicosis. Comment: Classified as simple silicosis because of suspect lung field markings, definite eggshell calcifications, and occupational history. Case not included in metal mine study group, however, because of 9 years employment in a lead smelter. FIGURE V,14.-Simple silicosis. Copper miner, white male, age 50, height 66 inches, weight 198 pounds. Occupational history: Repairman, operator, and supervisor of surface ore- crushing plant 27 years, all at one mine. Army, 3 years. Medical history: Negative except for influenza 2 years previously. Off work 3 days. Symptoms: Chest wheezing but only with colds. No shortness of breath. X-ray chest film: I.L.O. Classification 3p. Diagnosis: Simple silicosis, early. Comment: Fine punctiform opacities scattered diffusely throughout lung fields with no other pathology noted. Considered good example of early silicosis. Only (lust exposure had been 27 years in one copper ore-crushing surface plant. 170 1 171

, FIGURE V.15.-Simple silicosis. Copper miner, white male, age 63, height 67 inches, weight 140 pounds. Ocoupational history: General miner in copper mines 21 years. Hand tramming in gold mine 2 years. Medical history: Pneumonia in 1935, 9 days in hospital. No present symptoms. X-ray chest film: Classified as category 2m, meaning a moderate degree of micronodular infiltration. Diagnosis: Simple silicosis, early. Comment: No symptoms were associated with these early silicotic changes. 172 FIGURE V.16.-Simple silicosis. Mine crusher operator, white male, age ¢6, height 71", weight 167 pounds Occupational historp: Various jobs up to shift foreman at mine crusher operation. _ Medical history: All negative except "chest wheezes" with colds. No dyspnoea or other symptoms. X-ray chest film: Classified as 2m-AX, indicating moderate micronodular infil- tration of lung fields with a suspicion of beginning coalescence. Diagnosis: Simple silicosis, early. Comment: The ore-crushing mill operations were associated with a number of cases of simple silicosi.B. 173

m 1 r I FIGURE V.17.-Simple silicosis. Miner, male, age 45, height 69", weight 1.J2 pounds Occupational history: General metal miner 10 years (2 years in uranium mine). Miscellaneous underground jobs 5 years. Medical history: Rheumatism. Present symptoms: None. X-ray chest Jilm: Category 2n, meaning a moderate degree of nodular infiltration. Diagnosis: Simple silicosis. Comment: Original film was considered good example of I.L.O. Classification 2n. No symptoms of silicosis. 174 j h FIGURE V.18.-Complicated silicosis. Lead-zinc miner, white male, age 45, height 72", weight 155 pounds Occupational history: Face miner 19 years; underground transportation 4 years. Med ical history: Off 28 days with pneumonia 3 years previously. Symptoms: None. X-ray chest film: Category A with 3n background. Small nodules diffusely scattered throughout chest. Small confluent areas both upper lobes. Diagnosis: Complicated silicosis, early. Comments: No symptoms were reported by this 45-year-old miner with early complicated silicosis.

FIGURE V.19.-Complicated silicosis. Miscellaneous metal miner, white male, age Iw, height 73", weight 165 pounds Occupational history: Underground inspector 5 years; general miner 16 years; ore-crushing plant 1 year. Medical history: None except he was told he had "dust on his lungs" in 1955. Symptoms: None. X-ray chest film: Category A with 3n background. Early confluence of opacities In both first interspaces. Hilar enlargement, emphysema, and slight distortion. Diagnosis: Complicated silicosis, early, and emphysema. Comments: This 42-year-old miner has diffuse nodular silicosis with small areas of coalescence. No symptoms were reported. FIGURE V.20.-Complicated silicosis. Copper miner, male, age 59, height 69", weight 119 pounds Occupational history: Driller and mucker 30 years; motorman 4 years; and laborer (nonmining) 5 years. Medical history: Negative. Symptoms: Wheezing in chest, constant productive cough, slight' shortness of breath. X-ray chest film: Category B with 3m background. Emphysematous areas and slight pleural thickening. Diagnosis: Complicated silicosis, moderately advanced. Comments: I.L.O. Classification B-3m. Moderately advanced complicated sili- cosis with moderate symptoms in a copper miner working 34 years underground. 176 177

i FIGURE V.21.-Complicated silicosis. Lead-zinc miner and supervisor, white male, age 55, height 71 inches, weight 180 pounds. Occupational history: General miner 6 years • supervisory positions, part time underground, in several mines, 26 years. Medical history: Recurrent fever and chest pain past 3 years. Has known he has silicosis for 20 years with progression of X-ray findings. Occasional at- tacks of "rhetunatism." Several light attacks of "llu" during past 3 years. Symptoms: Slight shortness of breath. X-ray chest film: Category 11 with 3m background. Fine micronodulations dif- fusely scattered throughout lungs. Moderate coalescence both upper lobes. Diagnosis: Complicated silicosis, ;moderately advanced. Comments: Although in supervisory positions during most of his mining career, he has spent a considerable amount of time underground especially during the early years. FIGURE V.22.-Complicated silicosis. Copper miner, white male, age 66, height 69 inches, weight 138 pounds. Occupational history: Underground pump operator and mucker 20 years; sur- face pump operator 6 years. L_arlier jobs included truckdriving, ranching, and construction work. jledical history: Denied any past illnesses or present symptoms. X-ray chest film: Category C with 3n background. Eggshell calcifications, em- physenia, both apices and bases, left hiluin elevated, distortion in intrathoracic structures, and pleural changes. Confluent areas in both middle and upper zones. Diagnosis: Advanced complicated silicosis. Comntents: I)espite the X-ray evidence of advanced silicosis, this miner did not report any positive medical history or symptoms. 178 179

HEALTH SERV ICES A health service data record was completed for each of the 50 mines where a medical survey was made. It contained information relating to the provision of hospital services, physicians, nurses, first-aid equip- ment, preplacement and periodic examinations, sickness absentee rec- ords, health and safety provisions, washing and toilet facilities, and change rooms. Table V.26 shows that company hospitals were operated by one- fourth of the mines. Of the 12 company hospitals 9 were at mines with 300 or more employees. Neither company hospitals nor full- time physicians or nurses were found in mines with less than 100 em- ployees. Among the 21 mines with 100-299 employees, 33.3 percent had full-time physicians and 38.1 percent had full-time nurses. Among the 11 mines with 300-699 employees, 63.6 percent had full- time physicians and a similar percentage had full-time nurses. The 7 largest mines, those with 700 or more employees, had slightly higher percentages. In addition, one mine specified a part-time physician and two mines a part-time nurse. There were 27 mines or 54.0 per- cent which did not have any full- or part-time service of a physician or a nurse. TABLE V.26. Number of 50 metal mines* having specified health services according to size of mine Number of employees 'rype of heaith services Total Less than 100 100-299 300-699 700 or more Number of mines---------------------- 50 11 21 11 7 Number of employees------------------ 19,172 687 4,237 7,443 6,805 Health services at mines: Company hospital----------------- 12 0 3 4 5 Full-time physician---------------- 19 0 7 7 5 Full-time nurse------------------- 21 0 8 7 6 Preemployment examination: Physical---------------------- 44 7 19 11 7 Chest X-ray------------------ 43 8 18 10 7 Periodic examination: Physical---------------------- 18 4 7 4 3 Chest X-ray------------------ 16 4 5 4 3 •Escludes uranium mines. Except in the smallest mines, preemployment physical examinations and preemployment X-ray chest films were usually made. All mines with 300 or more employees had preemployment physical examinations and all but one of these included X-ray chest films. Regularly sched- I I uled periodic examinations for all workers were much less common; 36.0 percent of the mines had such physical examinations and 32.0 percent included chest films. There was no definite trend according to size of mine for periodic examinations. In several additional mines there were regular chest film examinations, but only for certain classes of employees. It was reported that X-ray chest examinations were available upon request at several other lrlines but were not a routine procedure. Based on average mine employment there were 7,025 metal mine workers at the 16 mines which required periodic X-ray chest films for all employees. This represents only 36.6 percent of the workers at all 50 mines studied who had the benefit of this important preventive measure in silicosis control. The answers to questions pertaining to the provision of first-aid rooms, first-aid kits, and trained first-aid workers indicated that most of the mines had some type of these services with the exception that first-aid rooms were reported in less than one-half of the smallest mines. Responsibility for the enforcement of health and safety provisions was commonly under the direction of the safety department. Thirty- nine mines had a full-time safety engineer and six mines had part-time safety engineers, leaving five mines without this service. Three- fourths of the mines had a safety committee. REFERENCES 1. Fletcher, C. M., M.D. Short Questionnaire on Respiratory Symptoms. Committee on the Aetiology of Chronic Bronchitis, Medical Research Council, Postgraduate School of London, London W. 12, England. 1960. 2. Wright, B. M. and C. B. McKerrow. Maximum Forced Expiratory Flow Rate as a Measure of Ventilatory Capacity With a Description of a New Portable Instrument for_ Measuring It, British Medical Journal 2: 1041, 1959. 3. Hosey, A. D., V. M. Trasko, and H. B. Ashe. Control of Silicosis in Ver- mont Granite Industry. Progress Report. Public Health Service Pub. No. 557, Washington: U.S. Government Printing Office, 1957. 4. Flinn, R. H., W. C. Dreessen, T. I. Edwards, E. C. Riley, J. J. Bloomfield, R. R. Sayers, J. F. Cadden, and S. C. Rothman. Silicosis and Lead Poison- ing Among Pottery Workers. Public Health Bull. No. 244, Washington: U.S. Government Printing Office, 1939. (Out of print. ) 5. Dreessen, W. C., R. T. Page, J. W. Hough, V. M. Trasko, J. L. Jones, and R. W. Franks. Health and Working Environment of Non-Ferrous Metal Mine Workers. Public Health Bull. No. 277, Washington: U.S. Govern- ment Printing Office,1942. 6. Sayers, R. R., J. J. Bloomfield, M. J. Dalla Valle, R. R. Jones, W. C. Dreessen, D. K. Brundage, and R. H. Britten (with sections on autopsy material by J. W. Miller, and on silica in the urine and in lung specimens by F. H. ft 180 181

Goldman). Anthracosilicosis Among Hard Coal Miners. Public Health Bull. No. 221, Washington: U.S. Government Printing Office, 1935. (Out of print. ) 7. Flinn, R. H., H. E. Seifert, II. P. Brinton, J. L. Jones, and R. W. Franks. Soft Coal Miners Health and Working Environment. Public Health Bull. No. 270, Washington : U.S. Government Printing Office, 1941. 8. Cooper, W, C. and L. J. Cralley. Pneumoconiosis in Diatomite Mining and Processing. Public Health Service Pub. No. 601, Washington : U.S. Gov- ernment Printing Office, 1958. 9. Meeting of Experts on the International Classification of Radiographs of the Pneumoconioses. International Labour Office, Geneva, 1958. Occupational Safety and Health 19, No. 2, 1959. Additional Bibliography 10. Motley, H. L., M.D. Pulmonary Function Studies in Diatomaceous Earth Workers. 2. A Cross Section Survey of 98 Workers on the Job, Industrial Medicine and Surgery 29:370-378, August 1960. 11. Kory, R. C., R. Callahan, H. G. Boren, and J. C. Syner. The Veterans Ad- ministration-Army Cooperative Study of Pulmonary Function, American Journal of Medicine 30: 243-258, February 1961. 12. Cochrane, A. L., I. T. T. Higgins, Jacob Thomas. Pulmonary Ventilatory Functions of Coal Miners in Various Areas in Relation to the X-ray Category of Pneumoconiosis, British Journal of Preventive and Social Medicine 15 :1-11, January 1961. 13. de Hamel, F. A. The Grey Valley Survey-Smoking, Lung Function and the Effects of Dust in Coal Miners in New Zealand. Special Report No. 3, issued by Medical Statistics Branch, Department of Health, Wellington, February 1961. 14. Higgins, I. T. T. and P. D. Oldham. Ventilatory Capacity in Miners-A Five-Year Follow-Up Study, British Journal of Industrial Medicine 19: 65-76,1962. 15. Rogan, J. M., J. R. Ashford, P. J. Chapman, D. P. Duffield, J. W. J. Fay, and S. Rae. Pneumoconiosis and Respiratory Symptoms in Miners at Eight Collieries, British Medical Journal, 1: 1337-1342, 1961. 16. Nakamura, T. and T. Takishima. Cardiopulmonary Function Test in Pa- tients with Pneumoconiosis, Tohoku Journal of Experimental Medicine 73 : 335-348, March 1961. 17. Nakamura, T., T. Takizawa and T. Takishima. A Comparative Study of the Metal Miner's Silicosis and Coal Worker's Pneumoconiosis, Tohoku Journal of Experimental Medicine 73 : 309-334, March 1961. 18. Ebert, R. V. Summary of Symposium on Emphysema and the "Chronic Bronchitis" Syndrome, American Review of Respiratory Diseases 80: 209- 212, July 1959. 19. Vorwald, A. J. Diffuse Fibrogenic Pneumoconiosis, Industrial Medicine and' Surgery 29 : 353-358, August 1960. 20. Brinkman, G. L. and E. O. Coates, Jr. The Prevalence of Chronic Bronchi- tis in an Industrial Population, American Review of Respiratory Diseases 86 : 47-54, July 1962. 21. Nageischmidt, G. The Relation Between Lung Dust and Lung Pathology in Pneumoconiosis, British Journal of Industrial Medicine, 17: 247-259, October 1960. 22. Industrial Pulmonary Diseases. E. J. King and C. M. Fletcher, ed. Boston: Little, Brown & Co.,1960. 273 pp. 23. Inhaled Particles and S'apours. C. N. Davies, ed. New York: Pergamon Press, Inc., 1961. 24. Doyle, H. N. and R. H. Flinn. Silicosis Research, Mining Congress Journal, 43 : 126-129, Apri11957. :.5. Pendergrass, E. P. Silicosis and a Few of the Other Pneumoconioses: Ob- servations on Certain Aspects of the Problem, with Emphasis on the Role of the Radiologist, American Journal of Roentgenology 80: 1-41, 1958. 26. Schepers, G. W. H. Theories of the Causes of Silicosis, Industrial Medicine & Surgery, 29 : 326-333, 359-369, 434-439. 27. Parrish, H. bi. and H. B. Ashe. Epiilemiologic Methods in the Study of Silicosis, Archives of Environmental Health 1: 129-139, 1960. h 182 1 183

q .~ !5 CHAPTER VI A Retrospective Study of a Silicosis Control Program BACKGROUND IT WAS aEooaxizEn that the metal mine study could be strengthened if detailed retrospective environmental and medical data were available for study. Information of this kind was necessary to demonstrate the effect of a long-term environmental and medical control program on the incidence and prevalence of silicosis. The opportunity to study one such program was presented in 1959, when the attention of the Public Health Service and the Bureau of Mines was directed to a report issued by the Saranac Laboratory dealing with environmental and medical studies in certain mines of the Lake Superior district. This program had been inaugurated in 1933 by the late Dr. L. U. Gardner, who had gained worldwide recognition for his silicosis studies while associated with the Saranac Laboratory. Originally, nine mining companies participated in the activity, but in 1946, three of the companies discontinued the contract with the Saranac Labora- tory, and in 1946, 1954, and 1955, three other companies ceased operating. An unpublished report, entitled "A Survey of the Progress of 25 Years in the Control of Dust and Silicosis" prepared by the field division of the Saranac Laboratory in March 1959, was reviewed by the Public Health Service and the Bureau of Mines. This report supplemented a 20-year progress report which had been made in 1953. The report presented an X-ray classification of chest films taken on employees for the period 1934-58. This information is shown in table VI.1. It should be noted that the first four periods include five mining companies while the last period includes three companies. The strik- ing fact shown by this table is the steady decrease over the entire period for all classifications of abnormal X-ray findings, including the most minor changes. Among the workers examined in 1934-38, the percent with silicosis was 19.8. In succeeding periods, it fell to 12.4, 9.3 and 5.9 percent until there were only 3.4 percent with silicosis in 1954-58. Workers examined who had marked peritruncal exaggera- tion amounted to 11.0 percent in the first period and 3.1 percent in the last period. As would be expected, with the decrease in abnormal I 184 1 185

readings, the percent of workers with no peritruncal exaggeration rose from 44.2 to 83.8 percent. TABLE VI.1.-X-ray chest film classification (Saranac) of employees working in iron mines with contracts with the Saranac Laboratory by period examined X-ray chest film classification 1934-3g Examination period 1939-43 Total number of employees examined___________________ No peritruncal exaggeration____ Peritruncal exaggeration (PI) _ _ _ Marked peritruncal exaggera- tion (P:)------------ silicosis (Si, S2, Sa)------------ •Includes 5 mining companies. flncludes 8 mining companies. *5, 297 44.2 25.0 11.0 19.8 *7, 060 1944-48 *7, 165 1949-53 *7, 145 Percent of employees examined 63.4 17. 1 7.1 12.4 70.6 14.1 6.0 9.3 77.6 11.7 4.8 5.9 1954-58 t5, 049 83.8 9.7 3.1 3.4 Another part of this Saranac Laboratory report deals with the rec- ords of 271 individuals who had X-ray changes since 1934 that war- ranted an increase in their classification and had remained on the pay- rolls as of 1952 and 1953. Among the 48 men whose dust exposure was entirely in the 15 years (1937-53), there was a change from normal to peritruncal exaggeration (Pl) involving 40 men and from (Pl) to marked peritruncal exaggeration (P2) involving 8 men.* No man showed a progression which would be considered as silicotic. Men with exposure prior to 1937 did develop silicosis. * The 1959 Saranac Laboratory Report defines P, and P: classification of peritruncal exaggeration as follows: "PERITRUNCAL EXAGGERATION (P,).-The X-ray pattern is characterized by a slight accentuation of the shadows normally cast by the pulmonary blood vessels and is uniformly in evidence in both lung fields. "MARKED PERITRUNCAL EXAGGERATION (P:).-May be defined. as the general accentuation of the pulmonary linear markings, being quite pronounced and well defined, as described by Dr. Gardner, 'these changes, when associated with dust exposure, occur in the vascular sheathe making the vessels thicker than normal; consequently, heavier shadows are cast on the roentgenographic film.' Marked peritruncal exaggeration is rarely seen in the absence of dust exposure and can readily be accepted as evidence of pneumoconiosis, provided the exaggeration is uniform in the lung fields and there is a correlative industrial history." In the period 1954-58, 41 employees of companies in continuous operation through 1958 showed progressive chest X-ray changes. There were 24 men whose only exposure was in the 21 years (1937-58). One of these men progressed to silicosis, 14 went from normal to Pl, and 9 went from Pl to PZ. Seven of fifteen men with part of their ex- posure prior to 1937 progressed to silicosis. The report concludes with the statements :"X-ray changes indicat- ing the development of pneumoconiosis in this industry evolve very gradually. However, it seems reasonable to assume that sufficient time has not elapsed since the application of dust control to evaluate its effectiveness. With the exception of one case, no frank silicosis has developed from dust exposure subsequent to 1937, establishing the effi- cacy of control of free silica bearing dust. Pulmonary changes (Pl and PZ), ascribed mainly to the inhalation of dust considered incap- able of producing silicosis, have been indicated to a moderate degree by chest X-rays. Complete elimination of dust causing this type of benign reaction obviously is not obtainable in underground mines, but the reduction in the number of these cases over a 25-year period attests to the effectiveness of general dust control and further im- provement can be expected through constant maintenance of present detection and preventive procedures." Several meetings were held between representatives of the Bureau of Mines, the Public Health Service, the Saranac Laboratory, and the companies participating in the control program, at which time it was agreed that the information obtained by the Saranac Laboratory would be made available to the Public Health Service and the Bureau of Mines. Since it would have been a very time-consuming operation to review all of the available records, it was agreed that the following steps would be taken: (1) the Public Health Service would review a cross•section of X-ray chest films from the three mines included in the overall survey to determine if,there was a close correlation be- tween the readings of the Public Health Service and the Saranac Laboratory, and (2) the Bureau of Mines would review the environ- mental and historical records of these three mines. Insofar as pos- sible, a history of the dust control activities, together with the dates of installation of the various control measures, would be documented and if possible, the dust concentrations would be reconstructed uti- lizing the companies' information. However, a dust survey would be conducted by the Bureau of Mines to, determine the relationship be- tween counts as reported by the companies and those obtained by the Bureau of Mines. These two steps were taken between 1959 and 1961. It was determined that there was a close correlation between the X-ray readings of the Public Health Service and the Saranac Labora- tory. The Bureau of Mines was able to document fairly closely the history of dust control procedures in the various mines and ascertain 186 1 187

that the dust counts, reported in the companies' records, correlated closely with the dust counts obtained by the Bureau of Mines. Because this correlation of environmental and medical findings could be established, it was decided that it would be more expedient to make a detailed study of one participating mine rather than at- tempt to analyze a cross-section of all the data. After several con- ferences with the companies and representatives of the Saranac Labo- ratory, the Public Health Service and the Bureau of Mines suggested that the Montreal Mine, of the Oglebay Norton Co., be used for a thorough record study. The review of the historical data and in- formation relating to dust concentrations was started by the Bureau of Mines on September 11,1961, and completed October 25,1961. The Public Health Service study of the medical records was begun in December 1961 and completed in November 1962. The following sections report the results of this retrospective study which has served to confirm essentially the conclusions of the Saranac Laboratory and to demonstrate the effectiveness of a medical-environmental control program in the prevention of silicosis. THE STUDY OF MEDICAL RECORDS FROM ONE MINE The plan adopted for the medical record study of the Montreal mine was to record the X-ray readings on each man beginning with the first film taken by the Saranac Laboratory and continuing from year to year as long as he remained with the company. A similar year-to- year job history was recorded including any dusty work he might have done before entering employment of the company. A continuous work history was obtained and the reason for any periods he did not work was entered under "comments." The Public Health Service assumed responsibility for abstracting the data from the company and medical clinic records. A separate case history was prepared for each employee, consisting of two sheets, namely, the work history and the record of X-ray films taken. In order to be sure that no employee was omitted, a list was made con- taining each serial number issued under the Saranac Laboratory pro- gram. The first man whose X-ray was taken in 1933 was No. 1 and the series progressed without break until the last man, No. 2244, was reached in 1961. Once a man was assigned a Saranac Laboratory number, it was never changed so long as he remained with the same company, no matter how many X-ray films were subsequently taken. The following classes of individuals were excluded from considera- tion: persons with work experience at the mine of less than 1,year, persons in nonmining occupations such us male or female officeworkers, former employees who returned only for an X-ray chest film, and ap- plicants who had X-ray examinations but were not hired. A special effort was made, by searching insurance records and by consultation wih company officials, to learn the present status of the following classes of workers who were in the study group but had left mine employment: (1) all persons with silicosis or "infection" no matter how many years they had been employed; (2) all persons with 15 years or more of work experience in the mine. It was desired to ascertain if these former employees were now working elsewhere, were alive but not working, or if they had died and the cause. Copies of the official death certificates filed with insurance records, were found for most persons who had died, even those with short employment. The attempt was also made to find the reason for leaving employment, such as "quit," "fired," retired, or died for each person whose em- ployment was terminated. Preemployment work histories were secured from the clinical rec- ords made when a man was hired. After employment, it was possible to secure a month-by-month list of jobs held from official sources in the company employment office. Certain employees such as mechanics, pipemen, electricians, and other maintenance men are likely to spend part of their time on the surface and part underground. The actual years spent above and below ground were estimated after talks with officials who were familiar with working practices. One of the decisions made early in the planning stages of this study was that X-ray chest film interpretations made over the years by radi- ologists at the Saranac Laboratory would be compared with interpre- tations of the same films by the panel of radiologists who served with the Public Health Service on the Metal Mine Study. Since dual read- ings of all of the tens of thousands of serial films available would be an unwieldy task, and spot sampling was considered insufficient, it was decided that the latest filxtn on each man in the study would be read by the Public Health Service panel of radiologists. In addition, all men whose serial X-ray films showed any progression from normal to a silicotic category or to more advanced silicosis, according to the Saranac readers, were selected for special study. Each serial film from such men was read by the Public Health Service panel, as were a small group of films taken on other men which appeared to be of special interest. In comparing the results of the Saranac Laboratory readings and the Public Health Service readings, it was found that there was a close correlation between films classified as positive for silicosis by each group, with the Saranac Laboratory readers tending to classify more films as positive for silicosis than the Public Health Service readers. Thus, out of 99 silicosis cases classified positive by the Saranac readers, 74 were considered positive by the Public Health Service readers. 188 1 - 189

On the other hand, only five cases (out of the total of 1,293 men in- cluded in the study) were classified as positive for silicosis by the Public Health Service radiologists and not so classified by the Saranac Laboratory radiologists; these five, however, were classified by the latter as presilicotic. In studying the selected cases with serial films showing progression from a normal appearance to that consistent with silicosis, the two groups of film readings were in close agreement as to when definite silicotic changes appeared. Therefore, in view of this close agreement, all subsequent analyses of X-ray films presented here will be on the basis of the readings from the Saranac Laboratory, which provided an interpretation for every serial film in all cases. DESCRIPTION OF THE MEMBERS OF THE STUDY GROUP During the period when the Saranac Laboratory was examining workers at the selected mine, there were 2,244 separate case numbers issued from 1933 through 1961. Each of these individuals had one or more X-ray chest films taken, as it was the practice to conduct annual chest examinations on all underground workers and biennial exami- nations on surface workers. There were as many as 28 serial chest films in the files of some men. As explained previously, certain persons were eliminated from the study group. The following tabulation shows the number excluded according to a broad classification : Reason for exclusion: Number of uaorkers Worked less than 1 year----------------------------------- 359 Nonmining occupations----------------------------------- 222 Former employees---------------------------------------- 155 Applicants not hired------------------------------------- 215 Total excluded----------------------------------------- 951 The group with nonmining occupations included 47 female workers, 27 male white collar workers, and 148 men who were hired as pinsetters in the company-owned bowling alleys. The 155 former employees represented men who had not worked for the company since 1933, but came bf.ck to have additional chest films taken. The pre-,ent study is limited to the remaining 1,293 men. Of this number 396 men had been hired and were already working when the Saranac Laboratory records began on January 1, 1933. The total number of years they had worked at metal mines both before and after 1933 was as follows: 1-5 years, 46 men; 6-10 years, 45 men; 11-15 years, 60 men; 16-20 years, 63 men; 21-25 years, 71 men; and 26 years and over, 111 men. Among these men there were 116 at work prior to 1933 who remained with the company and were on the payroll at the time of the study in 1961-62. Table VI.2 shows the employment history of the 897 men who were hired in 1933 and subsequently. The number of years on the payroll is shown for groups of men entering employment between certain specified dates. Since 446, or 49.7 percent, of these men were still employed at the time of the present study, their total years of em- ployment were not completed. Also not taken into consideration is the fact that 201, or 22.4 percent, of the men had had other mining experience before being hired by this company. One-half of those with previous mining experience had worked less than four years, and 11.9 percent had worked 10 years or longer. None of the 897 men hired during 1933 or later had developed silicosis although 209 of these had worked 16 or more years in this mine. Included in the above group were 88 men who had already worked from 21 to 29 years without adverse effect at the time of the study. TABLE VI.2.-Distribution of workers hired in 1983 through 1960 according to year began working with the present company and number of years on the payroll Total number of Year began working with present company Number of years on pay- roll of present company men who began working 1933-60 1933-36 1937-40 1941-44 1945-48 1949-52 1953-56 1957-50 Total------- 897 113 121 217 151 201 88 6 1-5--------------- 299 18 36 91 55 53 40 6 6-10-------------- 216 26 22 28 9 83 48 11-15------------- 173 11 8 12 77 65 16-20------------- 121 6 20 85 10 21-25------------- 63 27 35 1 26-29------------- 25 25 It is interesting to note that 46.1 percent of the persons entering employment in 1933-36 continued to work for more than 20 years, 45.4 percent employed during 1937-40 worked more than 15 years, and 39.7 percent employed during 1941-44 worked more than 15 years. For each employment period, a large proportion were still working in 1962. Except during World War II, a relatively small percent worked for the shortest period, namely 1 through 5 years. It is apparent that men listed toward the bottom of each column in table VI.2 include many who were still employed at the time of the study. Higher up the column all men, of necessity, would have completed company employment. Among the 396 men working at the beginning of 1933, there were 83, or 21 percent, who showed evidence of silicosis. Sixteen additional 707-103 0-64-14

men in this group developed silicosis after 1933 while they continued in employment. These silicotic workers will be described in more detail in a later section. Because of the curtailed demand for iron ore, the men working in 1933 were a reduced portion of the normal labor force. Evidently the older and more experienced men remained at work, hence the concentration of workers with long experience in metal mining. The cause of death was known for 168 members of the study group, silicotic as well as nonsilicotic. Since it was not possible to trace the present status of all workers, other deaths have doubtless occurred which have not been recorded. Heart disease represented 42.8 percent of the known deaths, followed by 28.6 percent from violent causes such as industrial accidents, nonindustrial accidents, military action, and suicide. Cancer was the cause of 14.9 percent of the deaths and pneumonia of 5.4 percent. Only six deaths were attributed to pul- monary tuberculosis and there were two deaths attributed to cirrhosis of the liver. There was one death from each of the following causes : Brain abscess, enteritis, appendicitis, encephalitis, Addison's disease and peritonitis. WORKERS WITH SILICOSIS For the study group of 1,293 men, it was possible to estimate the prev- alence of silicosis among those at work in 4 different years. This is shown in the following tabulation : 1933 1940 1950 1960 Number at work during the year________________ *408 571 712 617 Number with silicosis during the year------------ 83 79 51 9 Percent with silicosis___________________________ 20.3 13.8 7.2 1.5 •Includes 396 men at work Jan. 1, plus 12 men employed during the year. By definition, the study group included only men who worked longer than 1 year at the mine. As the older men with lung experience before 1933 retired, few of the men remaining developed silicosis so that the prevalence fell rapidly. By 1960, there were only nine men with silicosis in the study group, a prevalence rate of 1.5 percent, which was the prevailing rate at the time of the Public Health Service study. At the time of the first X-ray examinations in 1933, 83 cases of sili- cosis were found in the study group. Of these, 55 were Aassified as Stage I silicosis and 28 as Stage II silicosis. After 1933, there were five of these men with Stage I whose X-ray reading changed to Stage II and one man with Stage II who changed to Stage III. In the years subsequent to 1933, there developed 16 more cases of Stage I silicosis among men who at first were negative. Each of these men had worked before 1933 as well as later. Not a single one of the total of 99 cases of silicosis found in the study occurred among men who had worked only since 1933. Table VI.3 shows for the 99 silicotic workers, their age and the years worked in metal mines at the time they terminated their employment with the iron mining company. It will be observed that three men were still at work at the close of 1961. More than two-thirds of these men were 60 years of age or older and 8.1 percent were 70 years or older at time of termination. A very small proportion, 6.1 percent, had worked less than 20 years in metal mines. Almost 40 percent had worked in this dusty trade for a total of 40 years or longer in- cluding some period of work after they had developed silicosis. TABLE VI.3.-Metal mine workers with silicosia according to age and years in mining when employment with the company was terminated Age of silieotic workers wben employment terminated Years in metal mining of silicotio workers when employment terminated Age in years Workers Years worked in metal mines Workers Number Percent Number Percent Total_-_-__ 99 100.0 Total________ 99 100.0 Under 50_____-___ 12 12.1 Under 20___________ 6 6.1 50-54------------ 7 7.1 20-24-------------- 6 6.1 55-59------------ *12 12.1 25-29-------------- 9 9.0 60-64------------ 22 22.2 30-34-------------- ti8 18.2 65-69------------ 38 38. 4' 35-39-------------- t21 21.2 70-74------------ 5 5.1 40-44-------------- t21 21.2 75 and over------- 3 3.0 45 and over-________ 18 18.2 "Includes 3 men who were still working In 1961. tlncludes 1 man who was still working in 1961. Among the 83 workers who were silicotic in 1933, approximately two-thirds had experience in two or more mines, while a third had worked in the study mine only. Table VI.4 shows the number of years in mining prior to 1933. Although it is not known how many years were required to produce the first evidence of silicosis, informa- tion is available on how many yeaTs these men had mined before 1933. Two-thirds had worked for 20 or more years. Men with min- ing experience less than 15 years represented one-third of the workers in one mine only and 10.5 percent of the workers in two or more mines. 192 ~ 193

TABLE VI.4.-Mining experience previous to 1933 of workers who had silicosis in 1998 by years worked in 1 mine only and in 2 or more mines Total years in mining prior to Number of workers Percen t of workers 1933 Total In 1 m onl ine y In 2 or min more es Total In lmine only In 2 m or more ines Total---------------- 83 27 56 100.0 100.0 100.0 Less than 10 years____ 3 3 0 3.6 IL 1 0 10-14--------------- 12 6 6 14.5 22.3 10.5 15-19--------------- 13 1 12 15.7 3.7 22.8 20-24--------------- 25 8 17 30.1 29.6 29.8 25-29--------------- 23 8 15 27.7 29.6 26.4 30 years and over_-___ 7 1 6 8.4 3.7 10.5 WORK HISTORY, SUBSEQUENT TO 1933, OF EMPLOYEES WITH SILICOSIS The work history of each man who had silicosis in 1933 or later can be traced in detail beginning with 1933 and continuing until he left employment with the mining company. These men fall into three groups : namely, 77 men with silicosis that did not progress, 6 men with silicosis that did progress, and 16 men working in 1933 who later de- veloped silicosis. The 77 men, who had silicosis in 1933 which did not progress con- tinued working for varying periods thereafter. Five of these men left employment in less than 5 years, 15 stopped in 5-9 years, 15 in 10-14 years, 22 in 15-19 years, and 20 men continued working for 20 years or longer. Table VI.5 shows the length of time worked for those who changed jobs within the one mine and those who continued in the same type of work until they left employment. As might be expected, the men who changed jobs stayed longer with the company than those who did not change. In the former group, 73.9 percent continued work- ing for 15 years or more, while in the latter group, 25.8 percent worked that long. When the occupation of the 311 men who did not change jobs was examined, it was found that 19 were underground miners. Seven of these continued mining for 15 years or more. Six men were supervisors and remained in supervisory positions, all for less than 15 years. Four powdermen worked less than 10 years. A track cleaner worked 8 years and a surface laborer worked 11 years. Among the 46 men, all underground, who changed jobs 1 or more times, 39 remained underground in various capacities and 7 moved to work on the surface. The jobs held by these silicotic men when they were first examined in 1933 were as follows: 35 miners, 3 shift bosses, 2 track cleaners, and 1 each trackman, pumpman, drill repair- man, slusherman, skip tender, and chuteman. Five of the seven men who moved to the surface were miners. Two-thirds of these 46 men spent 15 or more years in underground work after they had silicosis. All but one of the men who changed to the surface worked less than 10 years. TABLE VL5. Mining experience after 1933 of workers who had ailicosia in 1933 which did not progress, according to job status and years worked Number of years worked after 1933 Work history Total I 0-5 5--9 10-14 I 15-19 I 20 and over Number of workers Total -------------------- 77 5 15 15 22 20 Changed jobs 1 or more times__-- 46 0 4 8 19 15 Remained in same job_--__--____ 31 5 11 7 3 5 Percent of workers Total-_-_---_____--____-- 100.0 6.5 19.5 19.5 28.5 26.0 Changed jobs 1 or more times_-__ 100.0 0 8.7 17.4 41.3 32.6 Remained in same job_____----__ 100.0 16.1 35.5 22.6 9.7 16.1 Nine of the sixteen men who developed silicosis after 1933 were underground miners when they were classed as silicotic and remained miners until they left employment. Four men changed from under- ground to surface work at some time after they became silicotic. Three men who were on the surface at the time of their silicotic diagnosis remained on the surface. Years of mining experience at the time of diagnosis as silicosis were as follows: less than 20 years, 6 men; 20-29 years, 5 men; and 30 years or over, 5 men. The six men who changed from Stage I to Stage II silicosis or from Stage IT to Stabe III worked a relatively short time after the more severe stage was diagnosed. The number of years worked after the change in diagnosis were as follows: 1, 216192 11, and 12. Previously they had worked in the mining industry for 38, 36, 26, 22, 21, and 30 years, respectively. 194 1 195

The following tabulation shows the year in which each silicotic worker left employment in the mine : TABLE VI.6.-X-ray chest film readings by the Saranac Laboratory of workers with experience before and since 1938 by years in metal mines Year: Number of men Year-Continued Number of men 1935 2 1950 ------------------- 9 Lung 8eld markings- 1936 ---------------------- ---------------------- 2 1951 --- ---------------------- 3 6aranao reading 1937 ---------------------- 1 1952 ---------------------- 4 1939 ---------------------- 5 1953 ---------------------- 6 1940 ---------------------- 4 1954 ---------------------- 7 1941 ---------------------- 3 1955 ---------------------- 2 1942 ---------------------- 2 1956 ---------------------- 5 1943 ---------------------- 3 1957 ---------------------- 6 Total__________ 1944 ---------------------- 9 1958 ---------------------- 2 1945 ---------------------- 6 1959 ---------------------- 1 Normal______________ 1946 ---------------------- 1 1960 ---------------------- 5 P1------------------ 1947 ---------------------- 4 Working ------------------ 3 Pa------------------- 1949 ---------------------- 4 Siliootio______________ This indicates clearly that there was no wholesale dismissal of silicotic men, but there was a gradual departure as they reached retirement age or became unable to work any longer. Considering the fact that all of these men had worked before 1933 and that 83 men had silicosis in 1933, it is interesting that more than half remained in mine employment unti11950 or later. The present status of most of the 99 silicotic workers was deter- mined at the time of the survey in 1962. Thirty-two were known to be alive, 62 were known to be dead, and 5 were retired with status unknown. The cause of death was ascertained for 54 silicotic men. The largest group was 21 for heart disease, followed by 11 for cancer, 7 for accidents, 6 for tuberculosis, 3 for suicide, 3 for pneumonia, 2 for kidney disease, and 1 for Addison's disease. The proportion of deaths attributed to tuberculosis seems remarkably low among this small silicotic population although complete figures were not available. PRESILICOTIC CHANGES Table VI.6 shows a classification of workers by lung field radiologic markings according to years in metal mines for persons with some experience before 1933 and experience only in 1933 and later. All workers with a total of 10 years or more in one or more mines are included. It is once again noticeable that no case of silicosis occurred in the group with experience only since 1933. In addition, there ap- pears to be a notable decrease in presilicotic changes, especially marked peritruncal exaggeration (PZ), which drops from 15.6 percent in the group with earlier experience to 0.7 percent in the recent experience group. A comparison of men with 10-24 years in metal mining shows a decrease in the prevalence of P2 markings from 5.4 for the pre-1933 group to 0.5 percent for the group with experience only since 1933. Total__________ Normal______________ P1 ------------------- P9------------------- Silicotic______________ Total__________ Normal______________ Pi------------------- pa------------------ Silicotic_____ _ _ _ _ _ _ _ _ _ Total__________ Normal______________ PI------------------- PZ------------------- Silicotic_____ _ _ _ _ _ _ _ _ _ Years in metal mines Total 10-14 I 16-1fl I 20-24 2;2fl I 30-f- Number Some experience before 1933 444 27 39 45 53 280 105 14 14 11 14 52 172 11 19 25 25 92 69 1 2 3 5 58 *98 1 4 6 9 78 Experience only 1933 and later 426 188 133 75 30 405 185 127 67 26 18 2 6 7 3 3 1 1 1 Percent Some experience before 1933 100. o 100.0 100.0 100.0 100. 0 100.0 23.6 51.9 35.9 24.4 26.4 18.6 38.7 40.7 48.7 55.6 47.2 32.9 15. 6 3.7 5.1 6.7 9.4 20.7 22.1 3.7 10.3 13.3 17.0 27. $ Experience only 1933 and later 100. 0 100.0 100.0 100.0 100,0 95.1 98.4 95.5 89.3 86.7 4.2 1.1 4.5 9.3 10.0 .7 .5 1.4 3.3 •1 case less tban 10 years excluded. 196 f 197 = i II

A similar trend is observed in peritruncal exaggeration (P,), which decreases from 38.7 to 4.2 percent. Again, for persons with experience of 10-24 years the prevalence of Pl falls from 49.5 to 3.8 percent. Considering the normal films for persons with 10-24 years of ex- perience, the early group shows 35.1 percent while 95.7 percent of men working only since 1933 had chest X-rays which showed no evidence of silicosis. Another way of considering changes in X-ray markings is shown in table VI.7. Here, men with 10 years and more of work in the mine are placed in two groups: those who began working 1933-42, and those who began 1943-52. None developed silicosis, but 6.2 percent had some change in the first group and 1.3 percent in the second group. Except for one man who began in 1933-42 and worked 20 years, all changes were from normal to P3, the smallest amount of peritruncal exaggeration in the Saranac Laboratory classification. This table does not include the changes which may have taken place among men with less than 10 years work. It is remarkable that there were so few evidences of progressive X-ray changes in lung field markings in those time periods where dust induced changes are most likely. TABLE VI.7. Presilicotic changes in chest X-ray interpretation of men with 10 years or more of employment who began work in 1933-43 and 1943-62-Montreat mine X-ray chest fllm interpretation (Baranac Laboratory) Total Number of years worked in mine 16-14 15-19 1 20-24 1 25-29 Men who began work 1933-42 Total examined ------------------- 161 21 52 58 30 No change: Number---------------------------- 151 20 52 52 27 Percent---------------------------- 93.8 95.2 100.0 89.7 90.0 Change from normal to Pl---------------- 9 1 0 5 3 Change from P, to P$-------_------------ I 0 0 1 0 Percent with change--------------------- 6.2 4.8 0 10.3 10.0 Men who began work 1943-52 Total---------------------------- 225 158 67. No change: Number---------------------------- 222 157 65 Percent---------------------------- 98.7 99.4 97.0 Change from normal to Pt---------------- 3 1 2 Percent with change--------------------- 1.3 0.6 3.0 198 c , THE REVIEW OF ENVIRONMENTAL AND HISTORICAL RECORDS A study to obtain historical information on dust and related en- vironmental conditions was conducted in the period from September 11 to October 25, 1961, at the Montreal mine, Oglebay Norton Co., Montreal, Wis. Information was obtained from company files, by conferences with company personnel, and from Bureau of Mines files. All available and pertinent information on the history of the mine from the discovery of iron ore in 1885 through 1960 was reviewed. The wealth of data made available has been condensed considerably because of space limitations of this report. HISTORY OF OPERATIONS AND GENERAL INFORMATION Iron ore was first discovered within the present property limits of the Montreal mine in 1885. The first efforts to produce ore from the new discovery were by small open pit operations. At the time of the study, the Montreal mine property embraced the former Montreal, Trimble, Ottawa, and Section 33 mines. The first three of these mines recorded iron ore shipments in 1886 and shipments from the Section 33 mine were made in 1889. No record was found of the date when the first shaft was sunk on the property, but early underground production was obtained through numerous shallow shafts sunk at isolated spots along the strike of the iron formation. As the workings became more extensive and it be- came known that ore existed at greater depths, inclined shafts were sunk in the quartzite footwall. By 1912, iron ore was being mined through four shafts from the property now embraced by the Montreal mine. Two shafts on the west side were called the Montreal mine, and two shafts on the east side were called the Ottawa mine. Some- time prior to 1921, two five-compartment inclined shafts were sunk in the quartz slates 300 feet south of the footwall. These shafts re- placed the four old shafts and were operated independently as the Ot- tawa and Montreal mines. These two shafts, designated as Montreal No. 4 and Montreal No. 6, were still in service at the time of the study. A comprehensive geological study in 1920 revealed possibilities of orebodies at greater depth. An exploration program confirmed the geological deductions and determined the lateral limits of the ore to a considerable depth. A study of deep mining followed, and the pri- mary question was whether or not shafts at each end of the property should be continued or whether a new shaft should be sunk to handle total production. Furthermore, there was a block of unexplored 199

ground in the center of the property into which the orebodies were pitching. Sinking of a centrally located vertical shaft (No. 5) was begun on August 16, 1921. The shaft was 3,036 feet deep when completed in June 1928, and records revealed that it was sunk in at least three "lifts." The first 600 feet of the shaft passed through quartz slates and the remainder of the shaft was in greenstone. Connections to underground workings were made as each "lift" was completed. At the time of the study, No. 4 shaft was a ventilation and escape shaft. No. 5 shaft was the main hoisting and pumping shaft from the 35th level to surface. No. 6 shaft was used for hoisting men and supplies. Inside the mine an auxiliary shaft, sunk during the years 1951 to 1956 and located 1,100 feet north of No. 5 shaft, extended a vertical distance of 1,894 feet below the 31st level. This shaft was connected at several levels with the No. 4 and No. 6 shafts. Over the past 40 years, mine employment had varied between ap- proximately 300 and 900 men (see table VI.8). During this period 25 to 30 percent of mine employees worked on surface. During the study, the mine was worked two shifts a day, 5 days a week. Hoisting was conducted on three shifts. The mining places extended for about 6,000 feet in an east-west direction and from 3,000 to 4,000 feet below the surface. Average annual production for the past 20 years had been approximately 1 million tons of iron ore. GEOLOGY The Gogebic Range iron formation consists of a series of sedimen- tary rocks, with numerous intrusive diabase dikes. The members of the iron formation were easily identified and regular in both strike and dip, except where displaced by faulting. The footwall of the formation was a quartzite, grading dawnward into a slate and resting on a greenstone basement rock. The members of the iron formation in ascending order from the quartzite were the Plymouth, Yale slate, Norrie, Pence slate, Anvil, and other upper slates. The hard quartz- ite footwall and the middle band of Yale slates were in general, the impervious members of the formation. Productive horizons were the lower Plymouth, upper Yale, Norrie, and lower Pence. The bulk of the ore occurred in the Plymouth and Norrie members of the forma- tion. The Plymouth and Norrie members which overlay the ore bodies were composed of bands of very hard unaltered chert interspersed with bands of softer leached material. The ore was hematite and classified as soft. Most of it had a clay- like consistency with hard ribs throughout. Relatively large open- TABLE VL8. Statistical data on company operations in Montrea? mine Year Tons of ore produced Tons of rock hoisted Feet of entry work Average total employment 1921----------------- 151,138 35,813 11,130 311 1922----------------- 395,527 65,686 31,195 478 1923----------------- 792,942 55,051 40,503 757 1924----------------- 798,006 77,411 65,593 736 1925----------------- 912,056 123,649 64,825 798 1926------------------ 1,105,899 158,563 86,013 917 1927----------------- 1,162,116 103,053 57,500 802 1928------------------ 1,094,873 114,176 40,066 789 1929----------------- 1, 270, 370 97,761 43,973 896 1930----------------- 1,043,097 152,108 38,967 653 1931----------------- 753,992 90,580 20,010 448 1932----------------- 402,732 25,119 12,917 343 1933----------------- 210,289 21,995 6,133 360 1934----------------- 579,965 29,003 11,674 375 1935----------------- 678,127 69,187 9,933 430 1936----------------- 802,536 35,651 16,021 455 1937----------------- 953,810 68,759 24,971 508 1938----------------- 796,730 94,025 20,968 464 1939----------------- 808,973 109,741 17,802 559 1940----------------- 1,015,463 98,689 23,958 558 1941----------------- 1,080,136 96,798 26,758 609 1942----------------- 1,118,294 69,260 26,196 617 1943----------------- 1,120,793 84,494 14,227 641 1944----------------- 1,081,503 69,320 6,953 635 1945----------------- 1,113,929 50,296 6,467 585 1946----------------- 857,227 42,320 5,767 610 1947----------------- 1,153,196 57,765 7,855 638 1948----------------- 1,088,034 59,479 8,104 641 1949----------------- 962,119 58,943 8,184 658 1950----------------- 1,094,793 110,901 13,195 697 1951----------------- 1,119,703 127,166 15,507 715 1952----------------- 977,191 w 122,893 16,179 710 1953----------------- 1,126,144 155,380 19,522 729 1954----------------- 1,014,683 154,504 21,270 724 1955----------------- 981,633 150,933 22,625 727 1956----------------- 883,073 137,157 20,243 730 1957----------------- 966,049 190,597 25,552 733 1958----------------- 693,723 151,372 20,695 693 1959----------------- 490,490 68,564 10,184 639 1960----------------- 955,394 103,701 13,530 617 ings, especially under new capping, could be made in ore without im- mediate caving. Three grades of ore, Bessemer, non-Bessemer, and manganiferous, were produced. Through the years the ores have analyzed from approximately 57.5 to 60 percent iron, dry, and from 7.0 to nearly 9 percent silica. 200 201 I

Total and Free Silica Determinations Free silica determinations for the various members of the iron for- mation were not available. An analysis of greenstone samples made in 1936 revealed the following: free silica 0-12 percent, magnetite 2-7 percent, sericite 1-2 percent. The remainder was plagioclase, hornblende, epidote, etc. Another file notation stated that greenstone averaged about 10 percent free silica. A free silica determination made by the Bureau of Mines revealed that a composite sample of the ore hoisted in one day contained 4 per- cent free silica. Settled dust samples collected at various under- ground and headframe locations contained from 5 to 23 percent free silica. Numerous samples of the various members of the iron formation were analyzed for total silica. Averages of these analyses are tabu- lated below : Nomber of samples Material analyzed A tota pe verage l silica, rcent 13 Greenstone------------------------------------------- 58. 60 129 Quartzite and quartz slates____________________________ 65.70 11 Dike------------------------------------------------- 36.00 27 Cherty iron formation__________________________________ 36.23 10 Yale and Pence alates__________________________________ 43.88 Quartzite varied from a low of about 40 to a high of nearly 90 percent total silica, dike 18 to 45 percent, cherty iron formation 16 to 85 percent, and slates 27 to 63 percent. MINING METHODS Various methods of mining have been employed throughout the Montreal group of mines. In the early days of mining in the area an overhand, open-stoping method of mining was utilized. Entry into the mines was made through numerous shallow shafts sunk in the iron formation. Ore was hand mucked into end-dump tram cars and hand trammed to raises or the skip pocket. Wherever the hard strong ore persisted, the mining method was gradually changed to a sublevel open-stoping method with a 33-foot sublevel interval. The first sublevel above the haulage level was a mill raise and blasting sublevel. The block of ore to be stoped varied from 100 to 200 feet in height and was about 200 feet in length. Width of an orebody varied from 15 to 100 feet. Manway raises were driven through the orebody parallel to the quartzite footwall at in- tervals of 200 feet. These raises were connected by sublevel drifts at 33-foot inclined intervals. Midway between manway raises a mill raise was driven up through the orebody along the footwall and a slot was formed from footwall to hanging wall through the orebody. The ore was mined by widening the slot and then benching around the mill raise. Mining was accomplished by retreating to the manway raises. As the stope was enlarged additional mill raises on 25-foot centers were driven to intersect the stope. The sublevel open-stoping method of mining was terminated in 1940. In the western portion of the property, the soft, granular ore was developed by driving three or four parallel haulage drifts on 50-foot centers. Inclined raises were driven on alternate sides of the drift at intervals of 25 feet and extended to the top sublevel. Sublevel inter- vals were 25 feet and branch raises were driven to form a grid or checkerboard pattern of raises on 25-foot centers on each sublevel. With the introduction of double-drum electric slusher hoists in 1925, it was no longer necessary to drive so many raises. At that time, a series of raises was driven from main level crosscuts at about 33-foot intervals, and connections were made between raises on each sublevel. The ore then was slushed through these connecting drifts and cross- cuts to the raise on each sublevel. Cars of ore were loaded through chutes on the haulage level. Following the introduction of slushers on the mining sublevels, slushers were utilized for loading ore into cars on the haulage levels. However, due to the inability of the slusher operators to handle the ore from the innermost raises, a method of mining evolved whereby only one raise, a short distance from the crosscut, was driven up parallel to the footwall. Cross mucking then was begun on each sublevel and all ore from each block was trans- ferred to the loading drift through a single ore pass raise. At the time of the present study, ore was being mined by a sublevel caving method. Main level interval was 150 to 200 feet and the sub- level interval was 50 feet. Ore bodies were approached by main level drifts in the quartz slates south of thQ footwall. Main-level crosscuts were driven north from the slate-rock haulage drifts at intervals of 300 to 400 feet. Loading drifts, from which trains were loaded, were driven from main-level crosscuts into the ore bodies for about 60 feet. A single loading drift serviced a block of ore which measured from 20 to 150 feet from foot to hanging wall. A double-compartment mining raise, without chutes, was driven up from each loading drift parallel to the quartzite and about 35 feet from the mouth of cross- cuts. This raise was driven to the top sub, and subs were cut out at 50-foot intervals. On the top sub a crosscut was driven south into the footwall rock and a ventilation, supply, and manway raise was driven to the level above, holing through in rock. From the raise on 202 1 203

the top sub, a transfer drift was driven east and west approximately 150 to 200 feet in each direction or to the limits of the block. This completed the development of a 300- or 400-foot block of ground. Breaking ore by the sublevel caving method consisted of cross- cutting to the limits of the ore and breaking and caving the side and back pillars in retreat. The ore was blocked out in 50-foot pillars along the strike of the formation starting from a point 150 or 2Q0 feet east or west of the mining raise and retreating to the raise. In attacking a 50-foot pillar, two crosscuts were driven on 25-foot centers from the main transfer drift. A manway was made by raising midway between these crosscuts and driving an untimbered subcross- cut 25 feet above the mining sublevel. Openings from the inside of each crosscut were carried upward and enlarged until they broke through to each other and the manway suberosseut 25 feet above. From the manway subcrosscut the stope was enlarged from narrotiv benches. As slice holes were blasted in the walls, the back caved until it arched over the width of the opening created. Slicing was carried on until the protecting shell of ore around the stope was remarkably thin. Supporting ribs were then cut and the stope entered the drop- ping stage which continued for several shifts. The opening made was confined within the limits of the 50-foot-wide pillar. After the pillar was mined back to the transfer drift, during which time the legs were also removed between stope holes, a stope was opened on the footwall side of the slushing drift or over the drift in the same manner. HISTORY OF ORGANIZED SAFETY ACTIVITY A safety department was first organized during 1923. Records re- vealed that the department was headed by a safety engineer, but in- formation on the size and specific duties or objectives of the depart- ment could not be found. Sometime during the late 1920's the safety department was reor- ganized and a safety director was appointed. Under the director there were two safety engineers and three underground inspectors. Each inspector was assigned to one of the three shaft areas. The first ventilation engineer was hired in 1933, and through 1935 he devoted full time to ventilation, dust counting, dust control meas- ures, and recordkeeping. In 1936 the ventilation engineer was ap- pointed safety and ventilation engineer and was made the head of the safety department. About the same time, an assistant safety and ventilation engineer was added to the department, which, during the late 1930's was composed of four men. The safety department continued to perform safety and ventila- tion duties until 1954, at which time ventilation duties were trans- ferred to a separate supervisory department. At the time of the study, the safety department consisted of a safety director, an underground inspector, and a clerk who also did dust counting and certain surface inspections. First mention of the use of safety equipment was made during the sinking of the third "lift" of No. 5 shaft in 1928. Eye protection at that time was provided by wire-mesh goggles. At the time of the study, the use of hard hats, safety glasses, and safety footwear was mandatory. Other personal protective equip- ment or devices were provided where necessary and recommended. Respirators were required to be worn by miners during drilling and scraping operations. - First-aid boxes and equipment were provided at key points on sur- face and underground. A well-equipped first-aid room was provided in the central change house. - Meetings constituted an important part of the safety program. Information vital to the advancement of safety was discussed at weekly underground foremen's safety meetings and monthly Central Safety Committee meetings, which were attended by all foremen and top management. At these meetings, past accidents were reviewed, findings during safety inspections, and other pertinent safety infor- mation and fire prevention measures were discussed. The company had subscribed since 1940 to a service which pro- vided safety posters for bulletin board use on surface and un- derground, supervisory educational and training pamphlets, manage- ment information bulletins, and services in connection with mine suggestion system. Personnel from the mine had regularly partici- pated in safety programs and meetings sponsored or conducted by mining companies and other agencies. The company had maintained membership and had actively participated in the Lake Superior Mines Safety Council since the early 1920's and the mining section of the National Safety Council since the early 1930's. Numerous employees had received Bureau of Mines first-aid, mine rescue, and accident pre- vention training. Mine rescue crews were trained twice a month by company personnel. Mine air collected at several points throughout the mine was analyzed semiannually by the Bureau of Mines. The company had for many years maintained a doctor's office and provided medical care for employees. The date of constructing and equipping the first office could not be ascertained, but records were found which revealed that the company had purchased an X-ray ma- chine in 1914 and replaced it in 1928. New X-ray equipment was pur- chased in 1950. - From May 25 to November 1, 1933, the mine was temporarily closed for economic reasons. Prior to the closing about 470 employees were given physical examinations including chest X-rays. When the mine 204 1 - 205

reopened in November 1933, all employees were reexamined. This was the start of preemployment physical examinations. Late in 1933 the company began annual physical examinations for all underground employees. Surface employees received a physical examination every other year. Examinations were given as often as quarterly in occa- sional questionable cases. Hoistmen were given a complete physical examination every 6 months. Since 1941, the mining company had rented doctor's office space in a city-owned building and furnished the necessary equipment. An X-ray technician was employed full-time by Saranac Laboratories for duty at this office and one other on the Gogebic Range. A full-time qualified laboratory technician was provided by the company. Annual physical examinations were scheduled and arranged for by the safety department. VENTILATION In the early days of mining in this area, the shallow mines were sufficiently ventilated by natural means. The open-stoping method of mining created underground openings and eventual surface sub- sidence openings through which air could easily circulate. Natural ventilation, therefore, continued to provide circulation throughout the Ottawa and Montreal mines as long as the open-stope method of mining continued. This method of mining was practiced to a depth of nearly 3,000 feet on the east side of the property and to about 1,200 feet on the west side of the property. No records of fan installations, air quantities, or other ventilation data were found for the years prior to 1920. After sinking the central shaft (No. 5), which was completed in June 1928, company records and reports revealed that "a plentiful amount of air tended to flow through the mine`during the winter months, but during the hot summer months a shortage of air was noted in the workings on the western end of the property." Records revealed that at least 11 auxiliary fans ranging from 5 to 15 horse- power were in use throughout the property by June 1930. To relieve the lack of ventilation during summer months, a 60,000- c.f.m. Jeffrey Aerobladed rotary blower powered by a 25-hp. motor was installed on the 27th level, No. 5 shaft, in August 1930. This-is the first primary fan installation on record for this mine. In Decem- ber of 1931 a second primary fan, a 60-inch Jeffrey Aerovane fan powered by a 20-hp. motor, was installed on the 29th level of No. 5 shaft. It may be assumed that either or both fans were pulling air down No. 5 shaft, or from open stopes in No. 5 shaft territory, and forcing air toward No. 4 shaft workings as the records showed that No. i 5 shaft was maintained downcast in the early days and No. 4 shaft was upcast due to natural atmospheric pressures. In 1932 four No. 2i/2 Anaconda-type Troy Sorocco blower fans were put into service in various working places. This raised to 15 the total number of auxiliary fans on record at this time. No records were found to indicate where these fans were located or how much air was being coursed through underground workings. Reports revealed that after a ventilation engineer was hired, an in- tensive study of existing and proposed ventilation measures was undertaken. One of these reports, dated May 1933, was preparedd jointly by a representative of Saranac Laboratories and the company ventilation engineer. This report disclosed that the Montreal mine was divided into three main areas for ventilation purposes: The Nos. 4, 5, and 6 shaft territories. Air for No. 6 shaft territory entered the downcast No. 6 shaft to the 33d and 34th levels from where it was coursed westward and/or upward through workings and eventually vented into the open stopes in No. 5 shaft territory. Air for No. 5 shaft territory was drawn down No. 5 shaft to the 27th and 29th levels by the fans on each of these levels. The fan on the 27th level forced the air into the workings in the hanging wall formation. From the 27th level the air was coursed upward with the aid of auxiliary fans and ventilation doors. This air was exhausted into the open stopes west of No. 5 shaft above the 25th level. Air for the No. 4 ter- ritory entered the mine on the 29th level at No. 5 shaft. This air was forced westward through the haulage drift and haulage crosscuts to both the footwall and hangingwaIl workings in the No. 4 territory. The air was then coursed upward through raises and exhausted into No. 4 shaft on the 27th level. No record was made of the quantities of air available or the length of time the mine had been ventilated in this manner. This system of ventilating the mine had several disadvan- tages : Cold winter air was encountered on the levels and at the shaft by men coming from warm working places, ice formed in the shafts maintained downcast during the winter months, dust from activities in the shaft was carried into the mine with the downcast air, and dust was introduced to working places by moving air through raises countercurrent to the movement of ore. Several proposals for cor- recting these conditions were advanced. It was finally decided that No. 4 shaft should be maintained upcast, but experimentation was nec- essary to determine the best possible source of fresh air from the No. 5 and No. 6 territories. It was proposed that various sources of air and methods of circulation be tested experimentally. Dust, humidity, and temperature determinations were made and air velocities were measured at principal points throughout the entire mine during these ventilation experiments. Some of this experimentation was made ' 206 f , 207 , 707-103 0-64-15

in the late spring of 1933, but was halted when the mine was closed for economic reasons on May 25. In the fall of 1933 work was began on the construction of an air heating unit and fan installation at the collar of No. 4 shaft. It was decided to maintain No. 4 shaft upcast, but it was anticipated that air would have to be heated if it was ever decided to make No. 4 shaft downcast. About this time a decision also was made to obtain fresh air for No. 6 shaft territory from the open stopes in that area. Ac- cordingly, in November of 1933 a 40,000 c.f.m. fan was installed at the collar of No. 6 shaft and operated exhausting. The fan and heating unit installation begun in the fall of 1933 was completed at the collar of No. 4 shaft in September of 1934. The fan was operated exhaust- ing and drew approximately 65,000 c.f.m. through No. 4 territory and up No. 4 shaft. For most of the period from late 1933 through 1934, No. 5 shaft was maintained downcast. All primary fan installations were made to provide flexibility so that different schemes of ventila- tion could be tried experimentally. The foregoing discussion is presented to illustrate the degree of detail with which records of ventilation practices had been kept. As space limitation does not permit similar detailed account of venti- lation procedures and improvements throughout the life of the mine, the following salient data relating to ventilation are presented in summarized form : Before 1933 At least 11 auxiliary fans were in use by June 1930. First primary fan was installed in August 1930. Second primary fan was installed in December 1931. Four additional auxiliary fans were put into service in 1932. 1933-36 Full time of first ventilation engineer was devoted to ventilation, dust counting, and dust control measures. Mine air analysis started. A primary fan was installed at the collar of No. 4 shaft. A primary fan was installed at the collar of No. 6 shaft. Primary and auxiliary fans were continually being relocated to pro- vide ample circulation of air. Approximately 150,000 c.f.m. of air was being circulated through the mine at the close of this 4-year period. First installation of automatic ventilation doors which permitted the passage of ore trains without interrupting the main air current. 1937-40 A primary fan was installed on the 29th level of No. 5 shaft. Other primary fans were now located on the 33d level of No. 6 shaft, the 27th level of No. 5 shaft, and at the collar of No. 4 shaft. These four fans provided a total of 180,000 c.f.m. of air. The number of auxiliary fans was increased from 15 to about 30. Began driving special ventilation raises in rock to avoid contamina- tion of air being coursed to working places. 1941-44 A fifth primary fan was installed on the 31st level of No. 6 shaft. Forced ventilation was increased from 180,000 to 200,000 c.f.m. The number of auxiliary fans at the close of this period was 35. By the end of this period fresh air for the mine was being drawn through open stopes in No. 5 and No. 6 shaft territories. 194"8 Fresh air was supplied to lower levels in No. 6 shaft territory through a special rock ventilation raise driven from the 38th to the 35th level. Underground primary fans were relocated during this period, but forced ventilation was not increased. The number of auxiliary fans in use was increased from 35 to 53: 1949-52 A sixth primary fan was installed in the rock ventilation raise on the 38th level of No. 6 shaft. Forced ventilation was not increased. Special rock ventilation raise in the No. 6 shaft territory was driven from the 35th to the 33d level to provide a more positive access for fresh air. A total of 67 auxiliary ventilation units was now in service. 1953-56 One new primary fan was installed on the 37th level of No. 6 shaft to replace two of the three fans in service in that area. Forced venti- lation virtually unchanged. - The number of auxiliary fans was increased from 67 to 84. 1957-60. One new primary fan was installed on the 29th level of No. 5 shaft to replace the two old fans in service in this area. Forced ventilation was increased to 205,000 c.f.m. This was equiva- lent to about 750 c.f.m. of air per man on the maximum operating shift. A total of 81 auxiliary ventilation units was in service at the end of this period. 208 1 209

Other Ventilation Improvements Since 1935 mine air had been analyzed by the Bureau of Mines or by the company. All records indicated that mine air quality had been satisfactory. Weekly ventilation meetings attended by supervisory personnel were begun in April 1934. At the time of study, regularly scheduled ventilation meetings were no longer conducted, but shift bosses were responsible for reporting ventilation findings on their daily report forms. The ventilation engineer checked underground conditions al- most every day and made a monthly survey of quantities of air at main level intakes and exhausts. Special ventilation raises were maintained in rock to avoid con- tamination of air being coursed to working places. These special raises also insured more positive passage of air than forcing air up through caved material. Drifts, too, were driven in rock. A main reason for this was to insure openings for removal of exhaust air. Exhaust air from rock headings was discharged from the face through tubing and up a ventilation pipe in the auxiliary shaft to an aban- doned drift and then exhausted through the drift to No. 4 shaft. HISTORY OF DUST CONTROL Wet Drilling The earliest mention of wet drilling was found in a report dated 1922. At that time, 10 Ingersoll-Rand, No. 448, water-type drills were used in main level development work. A later mention of wet drilling was found in records covering the sinking of the third "lift" of No. 5 shaft. This shaft-sinking job was undertaken during the period from October 1927 to June 1928. Denver (Models 7 and 17), Ingersoll-Rand (N-72), and Sullivan (hand-held) drilling machines were used. Water was piped down the shaft to a manifold from which the water was supplied to the drill machines through 1/2-inch- diameter hoses. Throughout the 1920's, RB12 auger drills were used in ore. During 1933 and 1934, company dust counting and ventilation records indicated that tests were being conducted with wet and dry drilling. Most experiments were conducted during drifting and rais-. ing, primarily in rock. In February and March of 1934, experiments were conducted with Ruemelin dust traps during dry drilling and resin soap and pine oil emulsions in wet drilling. Neither of these proved very successful. Drilling in ore during this period, as far as could be determined, was still being performed almost exclusively with dry auger drills. d It could not be definitely determined just when 100 percent wet drilling was adopted. Various records indicated that early in 1934 Ingersoll-Rand Water-Leyner drills, types S-70 and N-72, were used for drift and raise work respectively. Drilling in ore was done both wet and dry for at least another year and possibly two. Records from late 1935 and early 1936 were somewhat contradictory, but it was con- cluded that wet, jackhammer-type, drills were used in hard ore and dry auger drills, which produced relatively little dust, were being used in soft ore. From available records, it can reasonably be assumed that 100 percent wet drilling was in effect by 1937. Other Use of Water to Control Dust Various means by which dust may be allayed with water were dis- cussed in nearly all company dust and ventilation records and reports dating back to January 1933. Evidences of earlier uses of water as a dust-control measure, other than wet drilling, were not found. Cross- connections between air and water lines were installed in 1933 and 1934. These connections enabled an air-water mixture (fog) to be blown into a heading after a blast. By the middle of 1934, records ; revealed that 13 "water blasts" were installed in underground ore places. Water blasts or sprays were installed and used whenever dust- producing operations in a working place contaminated air being coursed to other working places. At the time of the study, water was used liberally in all rock head- ings. The back, face, and sides of headings were wet down before drilling and after blasting. Muck piles were wet down before and; as required, during scraping. Shaft stations were wet down when they appeared to be dry and dusty. The underground crusher station was washed down at least two nights a week. Except for wet drilling and water sprays, (water curtains) as'required to allay dust in air enter- ing or leaving a heading, the use of water in ore places was avoided as much as possible. Other Improvements or Dust Control Measures Establishment of regular blasting times and close control of blasting practices had contributed greatly to reducing the exposure of miners to airborne dust. In 1933 consideration had been given to eliminating all blasting except immediately before the lunch period and at the end of the shift, but the records did not show when this practice first went into effect. Regulated hours for blasting were in effect at the time of the study, except in respect to blasting in rock headings that ex- haust air through vent tubing to abandoned drifts, and blasting in hung-up stope holes after barring had failed to cause ore to run. 210 211

Although not verified by experimentation and dust counting, com- pany officials felt that scraper loading instead of chute loading of tram cars produced less dust. It was evident that one loading point in each ore block instead of chutes at 25-foot intervals meant fewer dust-producing locations and enabled better dust control on the haul- age levels. Tests were made on various filter-type respirators during the first half of 1934, and within a year respirators were supplied to all men going underground. Orders concerning the use of respirators were circulated and posted. A copy of orders issued about 1935 is shown in figure VI.1. Air-line respirators were also introduced in late 1934 or early 1935. Their use was confined primarily to men working in rock headings. The use of air-line respirators was discontinued in. 1942. Approved filter-type respirators were issued to all underground workers at the time of the study. FIGURE. VI.1.-Orders to Captains and Bosses-Use of Respirators Under- ground. (Prepared in 1935 for Montreal mine.) Respirators are to be supplied to all men going underground and are to be worn during operations in ore or rock which produce dust and wherever dust is present. Chief dust-producing operations are- 1. Blasting. 2. Drilling with any type of drill including the auger. 3. Mucking with slusher hoist or shoveling by hand. 4. Running ore or rock from stopes 5. Loading cars from chutes. 6. Loading cars-with slusher hoist in loading drifts. 7. Loading skips at skip pockets. 8. Dumping cars at loading pockets. 9. Using blowpipe on cars, motors, drill-holes, etc. 10. Guniting. 11. Sweeping with brooms. Respirators should be washed by the miners at the end of the shift and kept in clean clothes lockers. Facelets should be changed when they become worn and frayed. Filter pads are to be changed every 4 hours and oftener where necessary as in wet drilling where pads soon become damp and difficult to breathe through. Dust Prevention Equilpment Water sprays are to be used in rock headings after blasting to wet down broken rock during mucking. Water blasta in rock headings are to be turned on for a period of 15 to 30 minutes immediately following blasting. The fine mist of the water blast settles dust produced in blasting and prevents it from mixing with fresh air currents. It also helps to kill gases and wets the heading. dus:iliary fans are to be used in all rock headings with fan tubing up close to the face. Leaks in tubing should be repaired promptly. Dust prevention and control measures were diligently pursued. Rules and regulations were formulated, circulated, and posted. A copy of Rules for Dust Prevention, prepared in 1936, is shown in figure VI.2. FsauaL VI.2.-The Montreal Mining Co., Rules for Dust Prevention. (Prepared In 1936. ) Rockwork Drilling. During all rock drilling in any part of the mine, miners must wear air-line respirators. Others coming into the heading for inspection or other purposes, must wear a respirator. Mucking. Muck piles must be wetted down during entire mucking period and miners in the heading must wear approved respirators. Blasting. Blasting is to be done only at the end of the shift unless the smoke and dust pass directly to the main air outlet and nobody Is working in the path of the smoke and dust. After blasting, the face and walls of the heading must be washed down with a hose before any work is done. Ventilation. All rock piaces must be ventilated with an auxiliary fan set in the fresh air current and provided with metal pipe and Ventube, with end of Ventube kept up to a point not more than 25 feet from the face. No fan is necessary where the working place is in a main fresh air current. Orework Miners are required to wear the ordinary respirators during drilling, slushing, and on entering working places after blasting. After drilling or slushing is finished, miner should continue to wear the respirator for a reasonable length of time. Blasting should be done at the noon hour or end of the shift wherever the working cycle can be so arranged. Miners must wait in the fresh air current for places to clear after blasting. COMPANY hUST COUNTS Late in 1932 or very early in 1933, specialists from Saranac Labora- tories were consulted concerning ventilation problems and dust-con- trol measures. Dust sampling and dust counting by company personnel were begun early in 1933. About 250 samples were collected and recorded during the first year of sampling. Samples were col- lected in both ore and rock places during drilling, mucking, timbering, and general working operations. Tables VI.9 and VI.10 show the average company dust counts by operations in ore and rock respectively. Almost 5,500 samples were reviewed, categorized by operation•, and averaged to prepare these tables. Only samples representing typical mining operations were included. 212 213

Samples collected during the years 1933 to 1949 iriclusive were spot check samples of the various operations with, generally, little or no contamination of the atmosphere by mining operations other than the one being sampled. For this reason, the dust concentrations ob- tained during these years could be interpreted as being somewhat low. Bureau of Mines personnel conducted a dust study at the Montreal mine during July and August 1936. During this study, 15 duplicate samples were collected. One sample was collected by Bureau per- sonnel and the other by company personnel. These duplicate samples served to check each other's methods. Company and Bureau samplers both used the Greenburg-Smith impinger. The collecting medium TABLE VI.9.-Average company dust counts for operations in ore in Montreal mine Year Drilling Mucking Timbering General work Average all operations 1933--------------- 5.13 4.82 ---------- 2.40 *4.12 1934--------------- 6.07 9.76 13.65 4.49 *8. 49 1935--------------- 1.79 13.83 1.79 3.01 *5.10 1936--------------- 21.28 20.00 5.19 5.80 *13. 07 1937--------------- 5.53 1.95 ---------- 3.02 *3.50 1938--------------- 6.81 13.36 ---------- 2.69 *7.62 1939--------------- 7.54 6.09 4.04 3.79 *5.36 1940--------------- 14.07 7.72 4.58 2.14 *7.13 1941--------------- 11.75 3.33 ---------- 5.11 *6.73 1942--------------- 3.16 3.88 3.37 1.98 *3.10 1943--------------- 5.49 5.38 2.90 3. 15 *4.23 1944--------------- 4.42 5.45 2.90 3.32 *4.02 1945--------------- 5.30 5.42 2.50 3.38 *4.15 1946--------------- 4.59 5.84 2.93 1.74 *3.63 1947--------------- 5.55 5.09 1.93 2.44 *3.75 1948--------------- 3.89 4.66 1.71 2.67 *3.24 1949 --------------- 4.55 5.10 1.90 3. 14 *3.67 1950--------------- 3.70 4.86 2.67 2.60 **3.45 1951--------------- 2.67 5.55 1.61 1.77 **2.05 1952--------------- 4.30 6.89 2.59 4.01 **2.20 1953--------------- 3.67 5.16 1.83 3.01 **2.48 1954--------------- 3.60 7.70 1.80 1.70 **2.45 1955--------------- 3.18 8.57 1.65 3. 14 **2.64 1956--------------- 2.12 6.68 2.24 1.78 **2.24 1957--------------- 2.88 7.77 3.15 3.93 **3.16 1958--------------- 3.51 7.26 3.89 2.56 **3.55 1959--------------- 3.14 4.42 3.08 1.61 **2.27 1980--------------- 2.94 4.48 2.72 1.68 **2. 30 *Algebraic average. *•Weighted average (8-bour ezposure). used by the Bureau was alcohol. Distilled water was used'by company samplers. Samples were counted by identical methods. The first seven samples collected and quantitated by company methods were 30 to 70 percent lower than the duplicate Bureau samples. After adopt- ing Bureau recommendations and instructions for sampling and count- ing, company quantitations were usually within 5 percent of the duplicate Bureau samples. The Greenburg-Smith impinger was used to collect dust samples until June 1939. After that time the midget impinger was used. - - Average dust concentrations, as determined by company samples for the past several years, have been within recommended limits. During TABLE VI.10.-Average company dust counts for operations in rock in Montrea mine Year Drilling Mucking Timbering General work Average all operations 1933--------------- 17.27 4.16 1.96 1.31 *6. 18 1934--------------- 20.23 5.55 1.68 6.58 *8. 1935--------------- 8.84 9.08 4.38 2.95 *6. 31 1936--------------- 15.05 9.88 3.78 3.36 *8. 1937--------------- 8.23 9.67 12.00 5.65 *8. 1938--------------- 12.07 9.94 1.76 2.69 *6. 62 1939--------------- 5.54 8.16 2.84 1.64 *4. 04 1940--------------- 4.02 8.29 2.76 2.48 *4. 1941--------------- 3.08 5.68 1.83 1.76 *3. 1942--------------- 5.85 4.86 ---------- 2.50 1943--------------- 6.50 4.43 3.20 2.72 *4. 21 1944--------------- 4.45 5.67 2.62 3.11 *3. 96 1945--------------- 3.78 2.74 2.27 1.85 *2. 1946--------------- 6.13 3.76 1.83 1.96 '~2. 64 1947--------------- 6.30 4.31 1.87 2.53 *3. 27 1948--------------- 2.25 ~ 2.94 1.25 2.09 *2. 13 1949--------------- 4.09 3.44 1.26 1.87 *2. 67 1950--------------- 2.40 4.39 1.77 1.94 **2. 23 1951--------------- 2.69 3.60 1.66 2.12 **1. 62 1952--------------- 3.04 6.73 2.91 3.01 **1 . 88 1953__---_-_-----__ 2.20 4.25 1.93 2.30 **1. 82 1954--------------- 1.80 3.64 1.43 1.80 **1. 1955--------------- 3.30 3.76 3.20 2.53 **2. 1956--------------- 2.30 4.53 1.56 2.04 1957--------------- 2.47 3.51 1.58 1.87 1958--------------- 4.11 4.57 2.98 2.90 1959--------------- 3.46 4.60 2.77 2.24 **2. 57 1960--------------- 3.09 4.66 2.48 1.37 •Algebraic average. •*Weighted average (8-hour esposure). t I 214 215

the 5-year period, 1956-60, the average dust concentration for each cycle of operations in rock and ore was as follows : Drilling------------------------------------------- Mucking------------------------------------------ Timbering----------------------------------------- General work-------------------------------------- ore 2.92 6.12 3.03 2.31 Rook 3: 09 137 2.27 2.08 Some pertinent practices in dust control, and the dates of their adoption, are summarized: BEFORE 1933 Wet drilling was used in some main-level development work in 1922 and during shaft sinking in 1927 and 1928. 1933-36 Full time of first ventilation engineer was devoted to ventilation, dust counting, and dust control measures. Services of Saranac Laboratories were engaged on matters concern- ing ventilation, dust counting, and medical assistance. Experiments with wet drilling and use of dust collectors for dry drilling. Dust respirators were issued to underground miners. Air-line respirators were used by miners on rockwork. Water sprays and "water blasts" were installed, and water was used extensively for allaying dust. Regulated hours for blasting were first established. One hundred percent wet drilling was in effect by the close of this period. 1937-40 Dust respirators were used by miners drilling and mucking ore and mucking rock. Air-line respirators were used by miners duririg drilling in rock. A t I 216

A Classification of the Pneumoconioses (Geneva- TThe Use of the Nezv International Rqdiological - 1958) in the Study of Silicosis impeded international comparisons in the past, facilitates comparisons between industries, and makes comparisons within industries between different time periods more prac- ticable. Until the time of the 1958-61 revaluation of silicosis in the metal mining industry, the Public Health Service, the States, and other itself to good statistical evaluation, offers a beginning in overcoming the barriers of language and usage which have I THE cLassipicnTTON of the various abnormal lung patterns as seen in roentgenograms of individuals employed in dusty indultries has in- terested many investigators throughout the world over the years. The earlier international classifications of abnormalities in chest roentgeno- grams of pneumoconioses have been used in other countries much more than in the United States. Fletcher and his colIIeagues,l 2* Gilson and Hugh-Jones,8 and Van Mechelen and McLaughIitt,* have been. preeminent in their efforts in this area of endeavor and their recorded experiences and suggestions are most helpful and serve as important evaluations of international classifications. " The new international classification of radiological classification of roentgen observations in the pneumoconioses is a good tool and some of the advantages include the following : 1. It classifies the normal and abnormal patterns as seen in the roentgenograms into broad categories-negative, suspect, the several categories of simple and complicated pneumoco- niosis-and attempts to define the abnormalities by qualita- tive and quantitative descriptions that are included within the scope of each category. 2. By the provision of standard reference roentgenograms, visual examples are shown of the various abnormal patterns, which are more effective tools than text definitions and descriptions. 3. By providing standard definitions, terms, and symbols, it lends *Numbers refer to reference list at the end of the cbapter. 219

major research groups in the United States concerned with major studies of the pneumoconioses had not considered seriously the use of international classifications,5 but had used or modified existing film classifications. At the beginning of this study of the metal mine workers, however, the Public Health Service had recently participated in the 1958 I.L.O. meeting in Geneva which resulted in a revision of the 1950 I.L.O. radiologic classification.e The I.L.O. Geneva classification of 1958 stressed the value of achieving international application of the classi- fication to codify radiologic appearances in a simple reproducible way which would facilitate statistical and epidemiologic investigations to assess the size and nature of pneumoconiotic problems and determine the steps to be taken for the control of the disease and comparisons.of studies between industries and industrial countries. In planning the metal mine study, it was decided to insure expert and unbiased interpretations of the chest roentgenograms by a selected panel of radiologic consultants who would study and interpret the roentgenograms without any knowledge of the miner or of his occupa- tion within the mining industry. The consultants would not repre- sent either the mineowners, the labor unions, or any governmental agency. The three radiologists who were invited and agreed to serve on the panel were: Benjamin Felson, M.D., professor and director, Department of Radiology, University of Cincinnati College of Medicine, Cin- cinnati General Hospital, Cincinnati 29, Ohio. George Jacobson, M.D., professor and head, Department of Radio- logy, University of Southern California School of Medicine and Chief Radiologist, Los Angeles County Hospital, Los Angeles 33, California. Eugene P. Pendergrass, M.D., emeritus professor, Department of Radiology, Hospital of the University of Pennsylvania, Phil- adelphia 4, Pa. This newly formed panel of radiologists discussed the pros and cons of using the new 1958 I.L.O. classification at its first meeting early in 1959 and decided to attempt its use.* Although the I.L.O. sets of standard reference roentgenograms were not yet available, and did not become available in final form until many months later, an at- tempt was made to categorize each roentgenogram within the classi- fication according to the written definition and description of each category. After a trial period the panel became satisfied with the classification and used it throughout the study. These consultants *Subsequentiy the Pennsylvania Department of Health initiated a survey of central Pennsylvania coal miners in 1959 and also used the I.L.O. 19J8 classifi- cation in classifying the chest roentgenograms taken during the survey.7 read and reported their findings on each film independently to the Public Health Service upon specially prepared rating sheets supplied with each shipment of films. These separate readings and a con- sensus reading were then entered in the miners' records. The process of each panel member learning the new classification and applying it uniformly was somewhat difficult especially during the early months of the study. Wall charts were prepared for easy reference to the schematic presentation of the classification and to the basic definitions shown in figure VIL1. Discussions were held at each regular quarterly panel meeting to crystallize the panel's think- ing on classifying the roentgenograms which presented problems, especially in the "gray areas" between categories. As the study continued, the panel members gained valuable experi- ence in studying and interpreting a large number of roentgenograms. As a result of discussion and comparison of variations in interpretation at quarterly meetings, it was noted that a decreasing number of roent- genograms needed reconsideration. There were numerous problems, however, that arose from time to time that required special attention. With the large volume of roentgenograms being processed, it was not feasible to attempt to review all films at the quarterly meetings to reconcile disagreements in interpretation among the three members of the panel. Then, too, it was found that there was sometimes a lack of unanimity even after such a review and discussion. Under such circumstances, the "consensus interpretation" (reading) was developed on a majority rule basis, with certain exceptions. Examples of such include the following : 1. If two panelists selected the category "1m" and one selected "2n"; the consensus was °6lm" 2. If there were two who recorded "A," and one a"B," the con- sensus was entered as "$.." 3. If there were two °GZ" interpretations and the third was "0" or "2p," the consensus was "Z." 4. An exception to a majority obtained when there were two 11011 interpretations and one positive reading. The recording was "Z" which is a doubtful category based on a positive interpre- tation by one radiologist. In all of the readings of the "A," IB," or 11C' categories of con- glomerate and massive lesions which indicate complicated silicosis, an effort was made also to categorize the background of small opaci- ties. The majority rule held for qualitative and quantitative evalua- tion of the small opacities and the large lesions. Thus a"B2m," "C2n," and a`B3n" interpretation would be rated as a`B2n" con- sensus. It was possible to obtain a background reading on almost every roentgenogram on which the large opacities could be classified. 220 221

FIGURE VII.1.-I.L.O. radiological classification of chest films for Public Health Service metal mines survey Type of opacities. Fiim quality No pneu- Doubtful Fricuinooonlosis moconiosis small opacities Large opacities Quantitative features. 0 1 2 3 w d 0 Z AX A B C Qualitative features. m ~~ W o p m n p m n p m n Additional symbols. co I cp I cv I di I em I hi I p1 I px I tb I ea I cn I es I nt I ns Film quality. No pneumoconiosis. Doubtful opacities. Unsatisfactory film-impossible to read. Poor film-film of such quality as to make detailed classification difficult. O-No radiographic evidence of pneumoconiosis. Z-Increased lung markings. Uncertain as to diagnosis of silicosis. Pneumoconiosis Small opacities. The categorization depends on the extent and the profusion of the opacities: 1. A small number of opacities in an area equivalent to at least two anterior rib spaces and at the most not greater than one-third of the two lung fields. 2. Opacities more numerous and diffuse than in category 1 and distributed over most of the lung fields. 3. Very numerous profuse opacities covering the whole or rLearly the whole of the lung fields. The following types are defined according to the . greatest diameter of the predominant opacities: p-Punetiform opacities. Sizes up to 1.6 mm. m-Micronodular or miliary opacities. Greatest diameter between 1.5 mm. and 3 mm. n-Nodular opacities. Size between 3 and 10 mm. Large* opacities. co-Abnormal cardiac outline. ep--Cor pulmonaie. cv-Cavity. di-SigniHcant distortion. em-Marked empbysema. hi-Abnormal hiiar ahadoewas p1-Pleural abnormalities. *The background of amall opacities should be specified as far as possible. AX-Suspicion of large opacities or coalesence. A-An opacity having a longest diameter of between 1 and 5 cm. or several opacites each greater than 1 cm, the sum of whose longest diameters does not exceed 5 cm. B-One or more opacities, larger or more numerous than those in category A, whose combined area does not ezeeed% of 1 lung field. C-One or more large opacities whose combined area exceeds % of 1 lung field. Additional ayucbols pz-Pneumothoraz tb-Taberculosis saspectL ca-Cancer snspect. m--Calcified nodules in amaII opacities. es-Eggshell calcification. nt-Nontnbercuions infection. ns-Probably not siiicosis.

The question of the "L" category indicating numerous linear or reticular opacities within the pneumoconiosis classification was a prob- lem from the beginning of the study. The "L" designation appeared infrequently on the panel's interpretation and, when it did, there was lack of agreement. Accordingly, after using the "L" category for many months, the panel agreed to omit this category from the classi- fication sheets. This did not affect the use of the "Z" category for roentgenograms considered to be "suspect" or "doubtful" because of the presence of abnormal lung markings or questionable nodules sug- gestive of silicosis. There are a group of shadows that are seen in the lower lung fields near the costophrenic sulci and the lateral chest wall in some of the metal mine workers. The lines have been considered by Kerley a and others and are commonly referred to as Kerley's "A," `B," and "C" lines. Some of the panel members believe that these lines when pres- ent represent abnormal changes and one member believes that he has recorded such changes in healthy chests without cardiac lesions and without harmful dust exposure. It is not thought that the I.L.O. classification (1958) is a finished product; in fact, an important conference was held in April 1962 with some of the pneumoconiosis investigators in the United Kingdom which provided additional suggested modifications of the classification that may lead to a better understanding and stimulation of its use by others. The need for additional symbols beyond the nine listed in the LL.O. classification to show other significant abnormalities of the chest was apparent soon after the study was begun. The last five symbols in the list recorded below were added to the checklist of additional symbols. co-abnormal cardiac outline. tb-tuberculosis suspect. cp--cor pulmonale. ca-cancer suspect. ev--cavity. cn-calcified nodules in small di-significant distortion. opacities. em-marked emphysema. es-eggshell calcification. hi-abnormal hilar shadows. nt-nontuberculous infection. pl-pleural abnormalities. ns-probably not silicosis. px pneumothorax. Old tuberculous scars and other lesions were described separately. as seemed desirable under "Remarks", and any likely significance noted. Ghon-like calcifications were not routinely recorded. During the course of the panel meetings, it was noted that rather frequently well-defined eggshell calcifications occurred in the hilar nodes in association with the characteristic lung field pattern of sili- cosis. After several discussions, which drew upon the ev'idence ob- tained in the study and upon the earlier experience of the panel, it t I was agreed to try to determine whether eggshell calcifications are a diagnostic sign of silicosis, even sometimes in the absence of other characteristic lung field markings. Accordingly, all roentgenograms previously interpreted showing any suggestion of eggshell calcifications were reviewed again in- dependently and again in discussion at the panel meetings. After considerable discussion it was agreed that shadows suggestive of eggshell calcification must meet certain well-defined criteria to be considered as a diagnostic sign of silicosis. These criteria are: 1. The presence of shell-like calcifications measuring up to 2 mm. in thickness in the peripheral zone of at least two lymph nodes. 2. These calcifications may be solid or broken. 3. In at least one of the lymph nodes the ringlike shadow must be complete. 4. The central portion of the lymph nodes may show, in addi- tion, speckled calcification. 5. The affected lymph node must be at least 1 cm. in its greatest diameter. Since the adoption of these criteria, 47 roentgenograms were classi- fied as showing well defined eggshell calcifications. Of these 47 roentgenograms, the lung field markings of 31 also were classified as showing simple or complicated silicosis,10 with Z or doubtful mark- ings, and 6 with an 0 or negative interpretation for the lung fields themselves. - Another problem that arose was that involved when a classifica- tion was made of a category (3m for example), indicating simple silicosis, but one or two of the readers thought there was a conglom- erate shadow which was suspect or positive for a large opacity. Ac- cordingly it was agreed to proyide an additional category "AX" signifying suspicion of a large opacity or coalescence in addition to the specified category indicating simple silicosis. Thus a consensus read- ing of 3mAX still denoted simple silicosis but indicated that either two readers thought it was also suspicious of complicated silicosis or that only one reader thought it showed evidence of the A category in addition to the 3m reading. Therefore, this coding of AX merely indicated that the roentgenogram in the simple silicosis category is also suspect in regard to complicated silicosis. It is believed that this is an important addition to the classification in suggesting a possible transition stage from simple to complicated pneumoconiosis. Variations in readings between the qualitative readings p, m, and n were observed rather frequently, especially between m and n. Sim- ilarly there were variations in the quantitative readings of categories 1, 2, and 3, especially between categories 2 and 3. Generally, however, two of the three panelists would agree on m versus n, and category 2 224 225

versus 3, so it was usually rather easy to arrive at a consensus for these categories. An exception would be when other problems were involved such as the third reader considering the roentgenographic findings outside of the grouping of simple silicosis. During the course of the quarterly meetings, the question arose on several occasions as to whether there was sufficient difference between categories 2 and 3 to justify what was often a difficult decision. The same question arose as to the distinction between the "m" and "n" sized nodules, which was frequently a problem. In both instances, it was agreed to continue using these categories. Another problem that came up for consideration late in the second year of the study was the retention of category 1. It was noted that this category had been utilized rather infrequently and there was often a problem as to whether the shadow pattern might rather be classified as category 2, or sometimes even Z or doubtful. At the same time, there was the possibility that as the panel had gained experience with the classification there may have been a change in practice in classify- ing such films in this category. The question of possible changes in reading practice also came up with regard to the Z or doubtful classi- fication. It was thought that the standards for reading this category might have changed over the 2-year period fil.ms were being read. Accordingly, it was agreed to reread independently all the cate- gory 1, and the category Z films read up to that time, i.e., through the first 40 mines surveyed during the study. The rereading of the category 1 roentgenograms satisfied the panel that the category should be retained as a useful one in the classification to show early silicosis. The rereading of the roentgenograms classified as Z or suspect showed that the panelists had been drawing closer together on their interpre- tations and that a sizable proportion of roentgenograms with a previ- ous consensus of Z had now reverted to the 0 or negative classification. The net result of these rereadings of both Z and category 1 films was to change a subtsantial number of roentgenograms from Z or "suspect" to the 0 or negative category. The analysis of chest films classified as negative or suspect with regard to silicosis, simple silicosis and complicated silicosis has been discussed in detail in chapter V, and the relationship of silicosis to the many variables in the metal mining industry has been shown. The relationship of the several categories of silicosis to dyspnoea or breathlessness was also described. Table VIL1 shows the I.L.O. categorical classification of all 476 chest films considered to be consistent• with a diagnosis of silicosis in the study group of 14,076 metal mine employees. It will be noted that in the 305 chest films showing simple silicosis, the great pre- ponderance of films, 213 in all, were classified as category 2, which seems to be typical of simple silicosis. Of these 213 category 2 films, a large majority, 163 cases, were classified as category m, meaning small opacities usually from 1.5 mm. to 3 mm. in diameter. Thus, the classification of 2m accounted for over one-half of the films showing evidence of simple silicosis. TABLE VII.1.-I.L.O. radiological classification of silicotic chest films in study group of 14,076 metal mine workers Grand total 476 305*___-____ Total 49 Category 1 p 2 1 Small opacities-simple sllicosis n Total Category 2 p 5 213 33 m 163 n 17 Large opacities-complicated slllcosis 171_____-___ 171_________ Category A Total t104 Total t104 16 p 4 m 42 2 62 m 72 3 19 n 21 Total **44 Total **44 Category B 1 2 3 Total 29 Total 0 p 0 'Includes 14 films eggshell only, without other classification. tlncludes 6 fllms ZA, 1 film A only. ••Includes 181m ZB. =Includes 1 film C only. 32 m 31 11 n 12 $23 Total $23 Category 3 p In n 8 17 4 Category 0 1 2 3 0 p 1 11 0 15 11~ n 6 Of the 171 chest films considered to indicate complicated silicosis, by far the largest number, 104, .vere considered to be in the least ad- vanced grade, category A-meaning a large opacity (ies), ranging from 1 cm. up to 5 cm. in the greatest diameter. Category B, indi- cating more advanced complicated silicosis, accounted for 44 cases, while the most advanced group, category C, contained only 23 cases or about 5 percent of all silicotic films. It was noted throughout this study that there were few of the far advanced silicotic films frequently observed in the early studies of the Public Health Service. In considering the background of small opacities of the 171 films included in the A, B, and C categories, the categories 2 and m again dominated the picture with 105 films classified as belonging in category 2, and 118 films showing category m opacities. A difference was noted in the most advanced category C, however, where about half of these films were also classified with a category 3 background and two- thirds also were classified as category m. 226 227

Table VIL2 shows the broad I.L.O. radiological classification of the 12,487 chest films from the 50 metal mines where length of exposure has been shown previously in chapter V. It will be noted that in the 3 broad years-of-exposure groups, the percent of normal or nonsilicotic films decreases from 97.6 percent to 82.6 percent. It will be noted that after 25 years of mining the rates of doubtful and silicotic cate- gories increases rather sharply in those categories with sufficient num- bers to make a valid comparison. TABLE VII.2.-I.L.O. categorization of lung field markings by years of work at 50 metal mines* Total Years at metal mines Lung field markings 0-25 25-34 35-/- Workers examined Number Percent Number Percent Number Percent Number Percent Total_-_ _ _ _ _ 12,487 100.0 10,744 100.0 1,221 100.0 522 100.0 Nonsilicotio_ _ _ _ _ _ _ 11,928 95. 5 10,482 97.6 1,015 83.1 431 82.6 Doubtful________ __ 133 1. 1 81 .7 36 2.9 16 3.1 Category 1________ 43 .4 21 .2 19 1.6 3 .6 Category 2____-___ 186 1.5 92 .9 68 5.6 26 5.0 Category 3________ 29 .2 14 .1 9 .7 6 1. 1 EggsheIl____--____ 14 .1 4 .0 6 .5 4 .7 Category A____-__ 97 .8 37 .3 40 3.3 20 3.8 Category B___-___ 39 .3 7 .1 18 1.5 14 2.7 Category C_______ 18 .1 6 .1 10 .8 2 .4 •Ezcludes uranium mine workers. Table VIL3 shows additional categorical listing of all 14,858 chest films taken in the X-ray survey including the 14,076 films included in the study group, and, in addition, the films which were not included for reasons discussed previously; such as more than 5 years of expo- sure in other dusty trades. Among the 337 films classified as simple silicosis, over two-thirds of the films were classified as 2m (182), lm (46), or 2p (36), with relatively few in the remaining categories of simple silicosis. Sixteen of the thirty-one eggshell cases not otherwise classified appear in this grouping. Of the 337 cases classified as simple silicosis, 138 films were also designated AX, meaning a suspicion of coalescence or large opacities. Of the 185 films classified as complicated silicosis, the largest num- bers in the detailed analysis fell within the categories A-2m (47), B-2m (25), A-Im (16), A-2n (15), A-3m (12), and C-2m (10), but there was a wide scatter throughout the other categories. TABLE VII.3.-I.L.O.detailed classifecation of all 14,858 chest roentgenograms taken in metal mines study, including 671 employees with ezposure in other dusty trades Number Percent Total workers-------------------------------------- 14,858 100 Nonsilicotics--------------------------------------------- 14,166 95.4 Doubtfulor suspect_______________________________________ 170 1. 1 Simplesilicosis------------------------------------------- *337 2.3 C ategory: ip---------------------------------------------- 2 0 Im---------------------------------------------- 46 .3 ln---------------------------------------------- 5 0 2p------ ---------------------------------------- 36 .3 2m---------------------------------------------- 182 1. 3 2n-----------------------------°--------------- 17 .1 3p---------------------------------------------- 9 .1 3m-------------------------- ~------------------- 19 .1 3n---------------------------------------------- 5 0 ES---------------------------------------------- 16 .1 Complicated silicosis______________________________________ 185 1. 2! Category: A-lm------------------------------------------- 16 .1 A-2p-------------------------------------------- 5 0 A-2m------------------------------------------- 47 3 A-2n-------------------------------------------- 15 .1 A-3p-------------------------------------------- 1 0 A-3m------------------------------------------- 12 .1 A-3n-------------------------------------------- 8 .1 A-Z--------------------------------------------- 7 0 A only------------------------------------------ 1 0 B-lm------------------------------------------- 1 0 B-2m ------------------------------------------- 25 2 B-2n-------------------- - ---------------------- .8 .1 B-3m------------------------------------------- 7 0 B-3n-------------------------------------------- 5 0 B-Z--------------------------------------------- 1 0 C-2m------------------------------------------- 10 .1 C-2n------------------------------------------- 3 0 C-3p----------------°-------------------------- 1 0 C-3m------------------------------------------- 8 .1 C-3n-------------------------------------------- 3 0 C only------------------------------------------ 1 0 '6lmple silicosis includes 138 cases in AX classification. 228 229

From the experience gained in this study of silicosis, the problem of classifying chest roentgenograms by three experienced interpreters is relatively simple within the broad I.L.O. groupings of small opacities, consistent with simple silicosis, and large opacities, con- sistent with complicated silicosis. There were somewhat greater problems involved in classifying roentgenograms in the gray zones between early silicotic changes, the doubtful or suspect groups, and a negative reading. Not infrequently there were one negative and two positive readings; one negative and two suspect readings; one positive, one suspect and one negative reading; or any combination of these early or borderline changes so important in evaluating pneumoconiosis control programs. While the experience gained by reading and dis- cussing a great volume of roentgenograms during this study reduced this problem very considerably, there is sometimes a real difference of opinion as to whether a given roentgenogram is within normal limits, or within the suspect or early silicotic categories. Apparently this situation occurs with any kind of classification. It is believed that the consensus rating of "Z" or doubtful is an important one to help with this problem. Serial film studies and special radiological tech- niques will reconcile many of the problem cases. REFERENCES 1. Fletcher, C. M., K. J. Mann, I. Davies, A. L. Cochrane, J. G. Gilson, and P. Hugh-Jones. Classification of Radiographic Appearances in Coalminers' Pneumoconiosis, Journal of the Faculty of Radiolopist8, 1: 40-60, 1949. 2. Fletcher, C. M. Classification of Roentgenograms in Pneumoconiosis, A.M.A. Archive8 of InduBtrial Health, 11: 17-28, 1955. 3. Gilson, J. C. and P. Hugh-Jones. Lung Fa unction in Coalworker's Pneumo- conlosis. Special Report Series No. 290, London : Medical Research Coun- cil, Her Majesty's Stationery Office, 1955. 4. Van Mechelen, V. and A. I. G. McLaughlin. The New International Classifi- cation of Radiographs of the Pneumoconioses, dnnaid of Occupational Hygiene, 4: 237-253, 1962. 5. Third International Conference of Experts on Pneumoconiosis (Sydney, 1950). I.L.O., Geneva, 1953. 6. Meeting of Experts on the International Classification of Radiographs of the Pneumoconioses. International Labour Office, Geneva, 1958. Occupational Safety and Health, 9, No. 2,1959. 7. Lieben, J., E. P. Pendergrass, and W. W. bicBride. Pneumoconiosis Study In Central Pennsylvania Coal Mines, Journal of Occupational Medicine, 8 : 493-506, November 1961. 8. Shanks, S. C. and P. Kerley. A Text-Book of X-ray Diapno8is. Chest, Vol. II : 52. Philadelphia and London : W. B. Saunders, 1962. APPENDIX Eects of Silicosis and Other Factors on Pulmonary Function INTRODUCTION THE TWO METHODS for making certain tests of pulmonary ventilatory function by a series of single maximal exhalations were described in chapter V, page 107. These tests were made with the Collins 6 liter recording vitalometer and the Wright peakflow meter. These instru- ments were selected as being suitable for use under the many conditions of testing encountered during the field study of silicosis in the met4l mining industry. Four measurements were made of pulmonary ventilation function : (1) Peak expiratory flow {PEF) measured in liters per minute; (2) forced expiratory 1-second volume (FEV:,) measured in liters; (3) forced vital capacity (FVC) measured in liters; and (4) forced ex- piratory 1-second volume divided by forced vital capacity (FEV,/ FVC) measured in percent. This section of the report deals primarily with the effects of silicosis on these pulmonary function test results. In addition, some estimates of the effects of other factors have been made. Factors believed to be relevant to pulmonary function testing, other than silicosis, and whiclt can be accounted for in this analysis include : 1. Height. 2. Age. 3. Smoking history. 4. Number of years in underground mining. 5. Total years in mining. As shown previously, X-ray evidence of silicosis was not found in men under 35 years of age; consequently they have been excluded from this presentation. For men 35 years of age and over, complete information was available for chest X-ray findings, a114 measures of pulmonary function, and all of the 5 other variables noted above on a total of 7,817 actively employed metal mine workers. The following analyses have been confined to these 7,817 men (there were no females in the study group). 230 1 231

EFFECTS OF SILICOSIS ON PULMONARY FUNCTION The effects of silicosis on pulmonary function were estimated by developing predicted test results on the basis of men without silicosis and comparing these with test results actually observed in men with silicosis. The 7,817 men included in this analysis have been classified on the basis of X-ray chest findings as follows : No. of Oasea Group 1: Those whose chest film was coded 0, meaning no X-ray evidence of silicosis or other pneumoconiosis, or 1, meaning suspected or doubtful pneumoconiosis ---------------------------------------------------- 7,404 Group 2: Those whose chest X-ray fflm was coded 2, meaning changes con- sistent with simple silicosis-------------- -------- ------------------- 267 Group 3: Those whose chest X-ray film was coded 3, meaning changes con- sistent with complicated silicosis------------------------------------ 146 These three groups are referred to in this report as the groups with no silicosis, simple silicosis, and complicated silicosis. Only 1.7 percent of the films in group 1 were coded 1; the rest were coded 0. Table A.1 shows the average values for each of the four measures of pulmonary ventilatory function tests for men with no silicosis, simple silicosis, and complicated silicosis. For every one of the four measurements of pulmonary function, the average value is less for those with silicosis than for those with no silicosis. Also, for every one of the four measurements, the average value is less for those with complicated silicosis than for those with simple silicosis. TABLE A.1.-Average values for four measurements of pulmonary function of metal mine workers 85 years of age and over with and without silicosis Metal mine workers with- Number of workers Measurement of pulmonary function No silicosis_____-_____________ Simple silicosis________________ Complicated silicosis___________ 7, 404 267 146 YEF 483 441 382 FEV, 296 2.61 2.41 FVQ 122 3.95 3.68 FEV,/FVO 70.1 66.3 63.1 The comparisons in table A.1 are complicated by the fact that the metal mine workers with silicosis tend to be older and to have worked more years in mining than those with no silicosis and, as noted above, these factors no doubt have some effect on pulmonary function. The decline observed in table A.1 cannot, therefore, be entirely attributed to silicosis. Table A.2 shows that the average metal mine worker with complicated silicosis was 8 years older and worked in under- ground mining 10 years longer than the average metal mine worker with no silicosis. He has also spent more total years in mining and he had a lower average code for smoking. The complete code for smoking which is used in this report is shown in table A.3 ; former smokers are given a relatively low value in the code. The lower aver- age smoking codes for workers with silicosis reflects the higher pro- portion of men among the silicotic gr9ups than among the nonsilicotic group who reported having discontinued smoking. TABLE A.2.-Average values for 5 factors of metal mine workers 85 years and over with and without silicosis Smoking Years in Total Metal mine workers with- Number of Height Age (code under- years workers (inches) (years) from 0 ground in to e0) mfning mining No silicosis_____________________ 7,404 68.9 46.2 32.4 11.4 16.5 Simple silicosis----------------- 267 68.5 62.6 30.3 19.7 24.9 Complicated silicosis____________ 146 68. 7 54.6 28.3 21.7 28.6 TABLE A.3.-Classification of the cigarette smoking history among metal mine workers Code 0 10 20 30 40 50 60 Deflnition Never smoked cigarettes. Former cigarette smoker (ceased smoking more than 1 year ago). Smoked for less than 10 years and now smokes less than % pack per day. Smoked for 10-24 years and now smokes less than j4 pack per day, or, smoked for less than 10 years and now smokes Y2-1 pack per day. Smoked for 25 or more years and now smokes less than f/z pack per day, or smoked for 10-24 years and now smokes %-1 pack per day, or smoked for less than 10 years and now smokes over 1 pack per day. Smoked for 25'or more years and now smokes Y2-1 pack per day, or smoked for 10-24 years and now smokes over 1 pack per day. Smoked for 25 years or more and now smokes over 1 pack per day. Table A.4 compares the pulmonary function test results observed among men with silicosis with test results which would be predicted from an analysis of the 7,404 active metal mine workers without sili- cosis. Predicted values were obtained in the following manner: The 7,404 metal mine workers with chest films that were negative for sili- cosis were used to establish a mathematical formula showing the simultaneous relation between pulmonary function and all five of the factors shown in table A.2, using a multiple regression technique. The resulting formulas are presented in table A.S. Only those coefficients that are statistically significant at the 1-percent level are shown in table A.S, which is discussed subsequently. 232 1 - , 233

TABLE A.4.-Comparison of, observed values of pulmonary funetions for metal mine workers 86 years of age and over who have ailicosia with values predicted from metal mine workers without ailicosis Metal mine workers with- PEF Measurement of pulmonary function FEVi FVC FEVI/FVC Simple silicosis: Predicted_________________ 457 2.72 3.94 68.0 Observed_________________ 441 2.61 3.95 66.3 Percent reduction__________ 4 4 0 3 Complicated silicosis: Predicted_________________ 453 2.67 3.89 67.4 Observed_________________ 382 2.41 3.68 63.1 Percent reduction__________ 16 10 5 6 Using the formulas in table A.5, the predicted value of pulmonary function can be computed using average values for the characteristics of height, age, smoking, years in underground mining, and total years in mining. These formulas were used to compute the predicted value of pulmonary function for groups with no silicosis but having the same average values for these characteristics as the metal mine work- ers with simple silicosis and with complicated silicosis. This was done by substituting in the formulas the average values for the char- acteristics of these groups as shown in table A.2. TABLE A.5.-Formulas relating 4 measurements of ptclmonary function to height, age, smoking, underground mining employment, and total mining employment for 7,404 metal mine workers 35 years of age and over with no silicosis Formulas PEF= 271.8+ 5.95X1- 3.83X,- 0.74X8-0.77X4 -f-0.67X6 FEV1= -0.432-{-0.0755X1-0.0344X2-0.0053X8-0.0026X, FVC=- 3.90+ 0.139X,- 0.029Xg-0.002X8 -0.004Xg FEVI/FVC= 123.86- 0.499X1- 0.355Xz- 0.092Xm- 0.071X4+0.049X6 Symbols: X,-aeight (inches). Xs-Age (years). X%-Amount of smoking (see table A.3). Xt- Number of years in underground metal mining. Xs- Total number of years in metal mining. To illustrate how these results were obtained, the computations are shown for obtaining the predicted value for PEF in a group hav- ing the average characteristics of metal mine workers with compli- cated silicosis, which is shown in table A.4 to be 453 liters/minute. Substitution of the values in Table A.2 for height, age, smoking, years in underground mining, and total years in mining into the formula for PEF yields: PEF= 271.8-1-5.95 X 68.7- 3.83 X 54.6-0.74 X 28.3-0.77 X 21.7 + 0.67 X 28.6 =271.8-I-408.765-209.118-20.942-16.709-f-19.162 =271.8-I-181.158 =453 liters/minute These computations yield a predicted value of 453 liters per minute for nonsilicotic metal mine workers having the same average char- acteristics as those with complicated silicosis; this can be compared with the average value of 382 liters per minute actually observed for the group with complicated silicosis as shown in table A.1. The per- cent reduction of the observed value from the predicted value is 16 percent. It must be borne in mind that there is a large amount of variation from one metal mine worker to another in the measurements of pul- monary function. Five of the factors that might produce this vari- ability have been taken into account in computing the reduction of 16 percent in PEF for metal mine workers with complicated silicosis. There are undoubtedly other factors affecting pulmonary function that have not been taken into account. If it is assumed that the f.re- quency of these other factors is no different among metal mine workers with complicated silicosis than it, is in those with no silicosis, then the reduction of 16 percent can be attributed to complicated silicosis. In table A.4, all the reductions in pulmonary function are statisti- cally significant at the 1 percent level, with the exception of FVC and FEVl/FVC for metal mine workers with simple silicosis. The formulas presented in table A.5 yield only approximations since in order to simplify the computations an assumption was made that the relationship of the independent variables (i.e., age, height, etc. ) to pulmonary function test results was linear and additive. In general, this assumption is probably valid and the formulas presented in table A.5 are useful in describing the contributions of each of the five variables studied to pulmonary function test results when average values near the mean values shown in table A.2 are used. The results may become less reliable as the characteristic values substituted in the formulas depart farther from the means shown in table A.2. i 234 1 235

EFFECTS OF OTHER FACTORS ON PULMONARY FUNCTION Table A.6 presents estimates of the separate effects of aging, smok- ing, and underground mining on pulmonary function test results. In compiling these data average values for miners without silicosis were assumed. For example, data for aging compares pulmonary function for a group of men without silicosis of average height, smoking, and work history (see table A.2), who are 35 years of age with a group otherwise comparable but who are 55 years of age. Similar compari- sons are made for men who do not smoke (smoking code 0) and heavy smokers (smoking code 60) ; and for men without a history of under- ground mining and men with 20 years of underground mining. TABLE A.6.-Average decline in 4 measurements of pulmonary function associated with 20 years of aging, smoking, and $0 years of underground mining, among metal mine workers 86 years of age and over without silicosis Predicted value of pulmonary function Measurement of pulmonary function PEF FEVI FVc FEV,/FVC Aging: For age 35------------------------ 526 3.36 4.53 74.1 For age 5b------------------------ 449 2.68 3.95 67.0 Percentreduction__________________ 16 23 14 10 Smoking: No smoking----------------------- 507 3.15 4.27 73.1 Heavy smoking____________________ 463 2.83 4.15 67.6 Percentreduction__________________ 9 10 3 8 Underground mining: No underground mining__-_________ 492 3.01 121 70.9 20 years underground mining__-_---_ 476 2.96 4.21 69.5 Percent reduction__________________ 3 2 0 2 It is apparent that of these three variables the effects of aging are by a considerable margin the most important. Underground mining, by the method of calculation used, had only a small effect on pulmo- nary function measurements when other relevant factors were held constant in this large group of metal mine workers with no X-ray evidence of silicosis. It is of interest to compare the effects of silicosis on pulmonary' function (shown in table A.4) with the effects of other variables (shown in table A.6) even though the data in tables A.4 and A.6 were derived somewhat differently. Generally it may be stated that com- plicated silicosis probably has almost as much effect on pulmonary function as 20 years of aging and that cigarette smoking is of con- siderable importance even when compared with silicosis. CORRELATION BETWEEN FOUR MEASUREMENTS OF PULMONARY FUNCTION To answer the question of how the four measurements of pulmonary function are related to each other, the correlation coefficient of each of the tests with each of the other tests was computed. This was done separately for each of the three groups of metal mine workers, i.e., those with no silicosis, those with simple silicosis, and those with complicated silicosis. The results are presented in table A.7. TABLE A.7.-Correlation coefficients among 4 measurements of pulmonary function for metal mine workers 85 years of age and over Correlation coefficient for workers with- Comparison of pulmonary function measurements No silicoeis Simple silicosis Complicated slllcosis FEVI with FVC-------------------------- 0. 74 0.70 0.67 FEVi with PEF__________________________ .68 .75 .72 FEVI with FEVI/FVC____________________ .63 .64 .60 FVC with PEF__.________________________ .46 .46 .69 FVC with FEVI/FVC_____________________ .03 .09 .26 PEF with FEVI/FVC_____________________ .52 .57 .70 All the correlation coefficients shown in table A.7 are statistically significant at the 1-percent level, with the exception of the correlation between FVC and FEV~/FVC in the 7,404 metal mine workers with no silicosis and the correlation between FVC and FEVl/FVC in the 267 metal mine workers with simple silicosis. These two correlations could easily have occurred by chance. Among the metal mine workers with no silicosis, the FEV, is highly correlated with FVC. When FEVl is divided by FVC, the ratio FEV1/FVC is no longer correlated highly with forced vital capacity. As would be expected, PEF is correlated more highly with FEV2 than with either of the other two measurements of pulmonary func- tion. For the group of metal mine workers with simple silicosis the cor- relation coefficients are about the same as for the group of nonsili- cotics. For the group of metal mine workers with complicated silicosis there are two departures from the correlation 'coefl'icients observed in the group with no silicosis and in the group with simple silicosis. The• first departure is that FEVl/FVC retains some degree of cor- relation with FVC even though the ratio contains FVC as the denom- inator. This probably reflects the fact that the denominator FVC is itself reduced on the average because these men have complicated 236 1 237

silicosis but that FEV, is reduced to an even greater degree with ad- vancing disease. The second departure is that the correlation coeffi- cient of PEF with FVC and with FEVl/FVC has increased con- siderably. This probably reflects the fact that when the silicosis is advanced, all the measurements of pulmonary function show reduced values and, therefore, correlate highly with each other. U.S. GOVERNMENT PRINTING OFFICE : 1461 0-707-103 238

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