Tobacco Documents Online

C, 3 National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20, 1977. (Issued November 1978) . THE MINING ENFORCEMENT AND SAFETY ADMINISTRATION - REGULATIONS AND METHODS Aurel Goodwin MESA - Metal and Nonmetal 4015 Wilson Blvd. Arlington, VA 22203 Abstract MESA regulations for exposure to asbestos require that no employee be exposed to airborne concentrations greater than 5 fibers/mL (soon to be reduced to 2 fibers/mL) greater than 5 micrometers in length on a time-weighted average basis. We are proceeding with public meetings to obtain necessary data to reduce this permissible exposure even further. We use the membrane filter method for sampling and phase contrast microscopy for counting. Our regulations specify that the term asbestos refers to chrysotile, amosite, crocidolite, anthophyl- lite asbestos, tremolite asbestos, and actinolite asbestos. In order to analyze for specific minerals we have contracted with Dr. Ruud at the University of Denver. Keywords: Asbestos; dust; fiber; metal and nonmetal mines; optical microscopy; phase contrast. The Mining Enforcement and Safety Administration (MESA) is responsible for adminis- tering two laws for occupational health and safety, The Federal Metal and Nonmetallic Mine Safety Act which was passed in 1966 and the Federal Coal Mine Health and Safety Act of 1969. Regulations for occupational exposure to asbestos have been promulgated under both Acts. The standard for coal mines which is found in Title 30 Code of Federal Regulations (30 CFR) Part 71.202 states: 71.202 Asbestos dust standard; measurement. (a) The 8-hour average airborne concentration of asbestos dust to which miners are exposed shall not exceed two fibers per cubic centimeter of air. Exposure to a concentration greater than two fibers per cubic centimeter of air, but not to exceed 10 fibers per cubic centimeter of air, may be permitted for a total of 1 hour each 8-hour day. As used in this subpart, the term asbestos means chrysotile, amosite, crocidolite, anthophyllite asbestos, tremolite asbestos, and actinolite asbestos, but does not include nonfibrous or non-asbestiform minerals.' (b) The determination of fiber concentration shall be made by counting all fibers longer than 5 micrometers in length and with a length-to-width ratio of at least 3 to 1 in at least 20 randomly selected fields using phase contrast microscopy at 400-450 magnification. The standard for metal and nonmetal mines which is found in 30 CFR Part 55.5-1(b), 56.5-1(b), and 57.5-1(b) states: (b) The 8-hour time-weighted average airborne concentration of asbestos dust to which employees are exposed shall not exceed 5 fibers per milliliter greater than 5 microns in length, as determined by the membrane filter method at 400-450 magnification (4 millimeter objective) phase contrast illumination. No employee shall be exposed at any time to airborne Preceding page blank 423

COS concentrations of asbestos fibers in excess of 10 fibers longer than 5 micrometers, per milliliter of air, as determined by the membrane filter method over a minimum sampling time of 15 minutes. "Asbestos" is a generic term for a member of hydrated silicates that, when crushed or processed, separate into flexible fibers made up of fibrils. Although there are many asbestos minerals, the term "asbestos" as used herein is limited to the following minerals: chrysotile, amosite, crocidolite, anthophyllite asbestos, tremolite asbestos, and actinolite asbestos. MESA has proposed a reduction for metal and nonmetal mines to provide the same exposure level as for coal mines, i.e., 2 fibers/mL for an 8-hour time-weighted average. This proposed change was published in the Federal Register on July 7, 1977. MESA uses the accepted industrial hygiene method of phase contrast microscopy for counting and the membrane filter method for sampling fibers. A detailed description of the method is given in the NIOSH Analytical Method P & CAM 239. There are several practical problems with this method for determining exposure. One of the more serious of these is the time and cost required for sampling and counting. In order to measure a worker's exposure, a sampling pump and filter are worn by the worker. Because a heavy accumulation of dust on the filter can hinder or prohibit sample counting, it is usually necessary to change the filter several times during a shift. Anywhere from 2 to 15 filters may be required to determine one person's exposure. Usually 5 to 8 filters are used. It costs a minimum of $10 to count each filter; thus the cost to determine one person's exposure for one shift ranges from $20 to $150. In addition, the cost of analyzing each sample for "asbestos" content increases this cost substantially. We do not have conclusive information on the cost of such analyses on a routine basis, but at present the cost for a single sample may be as high as $300 for electron microscopic analysis. Besides these counting and analyses costs, the industrial hygienist collecting the samples can, under average conditions, obtain reliable samples for only about five employees in one day. This may go to as high as ten employees under good circumstances, but in other mining situations it may be possible to cover only one or two employees. This will add another $10 to $20 for each sample. The total cost for determining time- weighted average exposure is therefore $400 - $500 if a single filter is sufficient for an electron microscope analysis, and could be as high as $3000 if ten filters are analyzed. In any event, the major contribution to cost is the mineralogical analysis by electron microscopy. The MESA Denver Technical Support Center is currently developing an innovative sampling pump which operates intermittently to obtain a time-weighted average exposure on a single filter. The sampling rate now being experimented with.is one minute out of every six minutes. That is, the pump is on for one minute and off for 5 minutes. The total "on time" of the pump is accumulated in a memory cell. This avoids the necessity for the industrial hygienist to precisely determine the on/off time of the pump. We will be testing this concept along with a conventional sampling• method, such as changing filters during the shift, in the next few weeks. If this is successful then the cost per time-weighted exposure will be reduced to only slightly over the cost of the electron microscopic analysis. Since a single filter would be sufficient to measure the total time-weighted exposure, only a single count and electron microscopic analysis would be needed for each full-shift, time-weighted average exposure. You might ask, "since it is necessary to use an electron microscope for analysis, why not also use it for counting?" Other than the fact that our current regulations specify the use of phase contrast microscopy, the added cost of electron microscopy for counting, and the correlation of such counts with disease prevalence or with the existing phase- contrast method, are factors which must be considered. However, there are no known technical problems with this approach. There are several other practical problems with sampling and counting asbestos using the membrane filter method and phase contrast microscopy. One of these is the non-uniformity in the deposition of dust on a filter, which occurs for a number of reasons. One of these reasons is non-uniformity in the filter manufacture. Figure-1 illustrates a pattern of deposition on some filter samples which were collected at a mining operation. The pattern is visible because the air in the workplace contained dark material (probably diesel smoke) which stands out when collected on the white filter. 424

G 5 Figure 1. Photograph showing uniform particulate density on filter. Usually such patterns are not visible because, when collecting fiber samples, only a light loading is desired and the collected material is often white. However, such patterns, when they do occur, can cause variations in counts between different counters and may be one cause for the non-uniformity discussed in P & CAM 239. Unfortunately, we have no quantitative data on the occurrence of such patterns or on their effect on counting precision. Another practical problem is that occasionally a filter, after being mounted, will show what are described by our microscopists as radial aggregates. Figure 2 illustrates this condition in an extreme case. Obviously,.such samples cannot be counted and would be rejected. Other "artifacts" which may be mistaken for fibers have been observed occasionally in some samples. However, they are usually distributed throughout the depth of the filter material and not on the surface, as is usual for filtered fibrous dust. These artifacts are similar to those obtained in the filters distributed_by NIOSH in Round 40 of the PAT program. 425 2063105214

Figure 2. Microphotograph showing radial aggregates that form in clearing filters for phase contrast microscopy. MESA participates in the NIOSH PAT program. We began the program with round 15 and have submitted acceptable results since that time on all subsequent PAT rounds. Although not without problems, the PAT program is worthwhile. One of the problems, however, for mine samples at least, is that the background of non-fibrous particles, as well as the kind of fibrous particles, differ greatly from those found on samples taken in work environments. Figure 3 is an example of a sample collected at a mine not expected to have asbestos. Figure 4 is an example of a PAT sample. It would be extremely difficult to detect fibers in the presence of dust, such as shown in figure 3, particularly if the level is less than current regulations permit. 426

Figure 3. Microphotograph showing typical dust sample collected in a non-asbestos mine. Figure 4. Microphotograph showing typical PAT sample for asbestos counting. 427

Here I would like to comment on one feature of optical microscopy which has led to some confusion among those persons responsible for counting fibers but who are not experts in optics. This is the concept of "resolution." To some people, "resolution" implies the minimum-sized object which can be seen. "Resolution" refers to the minimum distance between two objects which still allows them to be distinguished as separate. Particles smaller than the "resolution" distance can be seen as a diffraction pattern and hence, fibers as small as .0.1 micrometer (and perhaps smaller) can be reliably counted. Resolution will restrict the size of particles which can be analyzed by some optical microscope techniques. Hence, mineral identification by optical microscope will only be applicable in general to particles with dimensions greater than the microscope resolution. At present we do not do any mineral analyses using optical microscopic techniques. Most of the analyses that we have required have been done by Dr. Clay Ruud who discussed his methods earlier during this conference. Thus far, I have discussed some methodological and technical considerations inherent in MESA's enforcement of its asbestos fiber standard. Now I would like to address what I believe to be a more fundamental issue, namely, the merits of the standard itself. The Mining Enforcement and Safety Administration's current and proposed (revised) asbestos standard covers six minerals. At least four of these have definitely been associated with increased cancer incidence in humans. These are crocidolite, chrysotile, amosite, and anthophyllite asbestos. We also know that these four minerals produce tumors in experimental animals. Furthermore, we know that other mineral fibers, whatever their mineralogical nature, produce similar tumors in experimental animals, as reported in this conference by Dr. Mearl Stanton. As a result of these data, MESA proposed to its advisory committee that the asbestos standard be revised to cover all insoluble mineral fibers. In so doing we proposed to continue to use the existing phase contrast, membrane filter method for evaluation. Using the animal experiments to extrapolate from known human carcinogens to other substances in a similar class seems to me the prudent thing to do. This course of action would not only further reduce human risks, but also eliminate the need for an expensive electron microscopic or petrographic analysis to determine the mineral species of fibers. There is great concern among mine operators that such a general mineral fiber standard would impact upon every mining operation. All minerals are likely to have fragments that meet the criteria of 3 to I aspect ratio for particles longer than five micrometers in length and less than 5 micrometers in diameter. Obviously the impact of such a regulation would also depend on the permissible fiber concentration. If we believe the animal data is valid for extrapolating to humans for cancer induction, should we also not believe the animal data for setting fiber dimension? !f so, a minimum length of eight micrometers and a maximum diameter of 0.25 micrometers would be indicated by Dr. Stanton's work. These two parameters (length and diameter) would seen to be a more appropriate specification than an aspect ratio and minimum length. These seem to be the two critical parameters in animal studies for induction of tumors. In a "true" asbestos mining and milling operation, reasonable variation in these parameters will not greatly affect the fiber count. However, in an iron mine or a stone quarry, variations in these parameters could make a great deal of difference in the "fiber" count. If a particle is carcinogenic because of its size and shape, it should be counted; otherwise, it should be considered in another dust category, such as respirable silica or nuisance dust. I would ask the medical-biological researchers to review the infornatian on fiber dimension and arrive at a consensus an the appropriate fiber specifications and also whether the carcinogenic properties are due to chemical or physical properties. This is a crucial issue with the mining industry and is the cause for their great concern that the "asbestos" regulations will affect all mining operations. Finally, we need an estimate of risk vs exposure from the medical and biological researchers. It is impossible to set a rational standard without this information. To simply set all carcinogens to their lowest detectable limit does not make sense. It is easy to imagine two carcinogens, one very potent and the other weakly carcinogenic. It may be possible to measure the weak one at very low levels and the potent one only at relatively high levels. We should not spend our resources on controlling the weak one with low benefit while the other substance would be relatively uncontrolled. A rational 428

. CS and-equitable standard cannot be set, except perhaps a total ban on exposure to all carcinogens, without knowing the risks and benefits for any man-year's exposure. A total ban is not practical nor necessary for all carcinogens in our modern society. Discussion W. SMITH: Dr. Goodwin and others before him here have called upon the medical and biological people to comment on things that might give some clues about the estimate of risk. I am a physican and my patients are mice, hamsters, rats, and so forth, and I have some things to say that the hamsters have been telling us that would be pertinent to this question. We have used six different preparations of crysotile and we put these in the chest cavity, in the pleura space, of the hamsters. In our experiments with intrapleural injection of hamsters, we got many mesotheliomas in response to preparations of commercial asbestos that contained many fibers that I could see with 400X optical (phase) microscopy. We did not get mesotheliomas with three preparations of chrysotile that contained relatively few fibers that I could see with 400X (phase) microscopy. Our experience says that optical microscopy is a more pertinent method than electron microscopy for monitoring dusts for fibers. As I sat here this morning and saw the electron micrographs of these tiny fibers I feel that from what our hamsters are telling us those are not really the problem. Dr. Goodwin, does that give you any comfort in your using phase microscopy? A. GOODWIN: Well, yes, I believe what you have said is very helpful with our current regulation. However, I am also looking for future revisions to our regulations, both the exposure levels and, more importantly, are we looking at the correct minerals and the correct particles? For those materials that are generally agreed to be asbestoS there isn't a great deal of problem, but if we need to look at other minerals as well,.is the current definition of fiber too broad? ; E. HOOVER: You said we are going to see the mineral fiber standard again in the mining industry, and I missed a point. Are we going to be looking at a 3 to 7 aspect ratio? I thought I heard some reference to the numbers changing a bit; particles over 5 microns long and not wider than 5 microns? Or are we going to look at some other kind of criteria for the fiber standard? GOODWIN: No, I didn't say that we are necessarily going to have another standard in the mining industry. This is a long process, and advisory committees, public hearings, all these things precede any changes in our regulations. We had proposed to the advisory committee last year that the standard be revised to refer to mineral fibers rather than asbestos; and in that proposal we retained the current phase contrast microscopy technique for counting these fibers, i.e., fibers which have an aspect ratio of 3 to 1 and are greater than 5 microns in length. I am asking the biological and medical people if this is the correct interpretation of the information from animal and human studies. In other words, should we consider all mineral fibers that have a certain physical characteristic, and is this physical characteristic the one we are using now or should it be changed? HOOVER: I think in view of what you have said I wouldn't want that standard presented again until we can get the medical evidence to support it. I think you are aware of what we have heard here the last three days. Such a standard could wreak havoc on the mining industry in America. It is a serious problem when you define a mineral fiber to include everything, because as your records will indicate, many limestones can be inter- preted as being fibrous. I personally feel that this is a problem that will require additional medical studies before proposing a standard. One then has to try to live with it and see how many mining companies would be left after these standards are imposed. If you are thinking about this type of standard, certainly the threshold limit values would have to be adjusted upwards, I would think, because we would have a real problem going to the half of fiber per milliliter or 1/10 of a fiber per milliliter just based on what I have seen so far. Those are my comments, and I am very much concerned about the proposed standard; I have a feeling, I guess a fear that we are going to see it again. GOODWIN: Well, I can't say what will occur, but much of what I have given you is my opinion, but MESA has no plans to reintroduce a mineral fiber standard at the present time. When we proposed revising our regulation to reduce the standard we have now from 5 fibers 429 2063105218

OV t per milliliter to 2 fib.ers per milliliter we stated that we intend to consider further reductions in light of the OSHA proposal and in light of the NIOSH recommendations to OSHA. We will be conducting some informal meetings with the mining community in different areas of the country to discuss this reduction, however, before any such reductions are proposed. In these discussions we will be considering the NIOSH recommendations and the OSHA proposal which retains the current definition of asbestos and methods for analysis. HOOVER: One final question: I know with the new Secretary coming to the Interior Dept. that there was some comment about avoiding the use of the Advisory Committees since they, in effect, bottleneck the enforcement of the regulations. My concern is that if we go to a similar situation as we have in coal where we don't have an Advisory Committee to filter proposed standards, this would be a real problem. I would hope that the Advisory Committee will be able to be effective, as they were in September of 1976. GOODWIN: Well, I don't know what you are referring to about avoiding consulting with the Advisory Committee. Our current law requires that we consult with an Advisory Com- mittee. When I talk about having meetings and discussions with the mining community, this wasn't to circumvent that requirement. It was to get data that would be presented to the Advisory Committee, if we decided that the proposal to reduce the standard further would be prudent. W. CAMPBELL: If you change the 3 to 1 aspect ratio to 10 to 1, you will eliminate a lot of problems for all of us. I think we all agree that the cleavage fragments would not go beyond 10 to 1 or 15 to 1. So all this semantics of whether one has fibers or fragments could be fairly easy satisfied by going to 10 to I or a little higher aspect ratio. The 3 to 1 is really the basic problem, I think. 430