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2 Bruce G. Goodale Environmental Project Director NY State LOw Level Radioactive Waste Siting Commission 2 Third Street Troy, NY a2180 518-271-1;585 Oscar Hernandez Branch Chief US Environmental Protection Agency 11903 Antietam Road Woodbridge, VA 22192 Franca Gri1 l i Assistant Regulatory Toxicologist Hazardous Contamination Branch Ministry of' the Environment 135 St. C1' a.i r Avenue West Linda E. Jennett Director Environmental Affairs Schlumberger Env. Svces., Inc. 300 N. Main St., Suite 200 Greenville, SC 29601 803-233-0916 Suite 100 Toronto, Ontario, CAN M4V1P5 416-323-5076 Jong-Suk Kim Sidney E. Grossberg, M.D. Professor and Chairman Department of Microbiology Director-General Korean Ministry of Environment 635-298 Pongcheon 9-dong, Kwank-gu Seoul, Korea 617-432-4637 Medical College of Wisconsin 8701 Watert,Dwn Plank Rd. Milwaukee, WI 53226 414-257-8427 Betsey Kuhn Deputy Director Michael Gunn Asst. to the City manager City of Cincinnati Resources & Technology Division Economic Research Service 1301 New York Avenue, NW Washington, DC 20005 202-219-0449 801 P1 um Street, Rm. 24 Cincinnati, OH 45202 513-352-3790 Jeffrey Kutcher Aanel i a A. Hagen Acting Group Leader Lawrence Livermore National Lab Consutants in Epidemiology and Occupational Health 2428 Wisconsin Ave., NW Washington, DC 20007 202-333-2364 P0 Box 808, 7000 East Ave, L-255 Livermore, CA 94551 415-422-4278 Angela Li-Muller William C. Hayes Environmental Specialist Dow Chemical Company Senior Regulatory Toxicologist Ontario Ministry of the Environment 135 St. Clair Ave West Toronto, Ontario M4V 1P5 416-323-5114 V 2020 Dow Center Midland, MI 48674 517-636-2664 Mayada Logue O N ~11 Scientist Philip Morris v't ~ Jose E. Hernandez P0 Box 26603 Head, Indusi:ri al Hygi ene Dept. Richmond, VA 23261 ~ Navy Environrriental Health Center 804-274-3189 ~ 2510 Walmer Ave. © Norfolk, VA 23664 804-444-7575

TO: Continuing Education Participant~s ~ FROM: David A. S. Klipp, Program Coordinator RE: Telephone Locations and Protocol Here are the-telephone numbers which will serve to deliver messages to you during your stay with us at Harvard: During Class Hours: 617-432-1109 if that line is busy or there is no answer: 617-432-1171. We will take messages for you and post them either at the back of the classroom or at your place. In the event of an emergency, we will interrupt you in class. Here •is-•a- map-indicating (**)-the locations of the -four--public telephones in the School of Public Health: Lounge ** ~ ** (1st Floor) _ T I~ Elevators 11{11(stairway) -- ' \/ \) Classroom Hallway Lavatories PLEASE NOTE: ~ O ~ ~ Acknowledging the limited number of public telephones available C1Y here, we ask that you please try to consider keeping your calls 1$ brief and to a minimum. ~ ~ ~

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HARVARD MEDICAL AREA IKEY TO uaAPf I Rotch Bulldinp- 55 Shattuck Stre.t OTHER MEDICAL AREA FACILITIES 14 New Engiand Deaconeu Hoipital HARVAR D SCHOOL OF PUBLIC HEALTH • Francis A. Countway Librory of M.dklns 15 Beth Israel Hospital 2 Heelth Scimces :aboratovies, Dldgs, I ord 11 10 Shattuck Strett 16 Judqe Baker Guidance Center 665 Huntinpton Avenuo 9 Peter Bent Bripham HospitN 17 Boston Hospitat for Women (Lyin¢In Divkion) 10 Massochusatts MentaJ Health Canter 3 Sebastian S. Krage Educ®tiond F.cilidp Sullding 1e Madicat Ar®. Coop: 677 Huntlnptonb Avanut 11 Chlldren's Cancer Research Foundatlon 19 Jimmy Fund Auditorium 4 Henry LnSh.ttuclc International Houe. 12 Childnn'e Hospitd Medicta CentM 189-203-207 Park Drhrt 20 Harvard M.dicat School Labontory for Human 13 Shields Warren Radiation Latwr.tory Reproductlon.nd Repeoductive Biology HARVARD MEDICAL SCHOOL S Medical School Uwtdrangla 25 Shattuck ;itre.t 5A Harvard M.dica! School -Adminimadon Wpdky 3 V.nderbilt H.II -- 109 Av®nue Loui. P..tses (Medkal H.atth S.rvkatl HARVARD SCHOOL OF DENTAL MEDICINE 7 Hanard Schoot of Dantd M.edicin. 188 Lonp+vocb Av.atus Shattuck In- ~ternational House

SCIENCE AND ITS LIIVIa[TSo The Regulator's Dilemma Alvin M. Weinberg PROLOGUE: The shift in environmental concerns from visible pollution to more subtle threats, such as toxic pollutanis, presents special problems for regulators xho must fi4nction outside the limits of scientific certainly. The same handicap besets judges who tnust adjudicate disputes over claims for damages arising from new and hazardous technologies that involve adverse health effects that are latent or unpredictable. In this area of uncertainty in which accidental exposure to hazards is rare, scieni'i;,,ts resort to probabilistic risk assessment to estimate the likeli- hood and consequences of events that may carry a threat to human health. Such scienti,6c techniques for the investigation of rare events, however, often cannot provide definitive answers for regulators and judges. In this essaY phtsicist .9lvin Id'einberg suggests that instead of asking sci- entists for answers to unanswerable questions, regulators should settle for less-definitive answers and regulate on the basis of uncertainty. Technologi- cal ftxes, including greater reliance on inherent safetyfeatures that depend on the imnnutable laws of nature, can help reduce risk. But ultimately, says ti'einberg, it tna' y be necessary to establish some threshold beyond which blame for accidents and other untoward events would be unprovable and vic- tims would be compensated by a society as a whole. t Alvin A1. Id'einberg received his Ph.D. in physics from the University of Chicago in i' 939. He has been a leading figure in the development of nu- clear energy and has served as director of the Oak Ridge National Labora- ton- and as director of the Institute for Energy Analysis of the Oak Ridge Associated Universities. He is the coauthor of The Physical Theory of Neu- tron Chain Reaction (1958) and has written extensivelv on nuclear energy, nuclear proliferation, and the interaction between modern technology and s(X'iet 1'. FALL 1985 59

Despite the difficulties, scientific mechanisms have been devised for estimating, however imperfectly, the probability of rare events. For accidents the technique is probabilistic risk assessment (PRA); for low-level insults various empirical and theoretical approaches are used. Although probabilistic risk assessment had been used in the aerospace industry for a long time (for example, to predict the reliability of compo- nents), it first sprang into public prominence in 1975 with a reactor safety study directed by nuclear engineer Norman C. Rasmussen.3 The Rasmussen study, sponsored by the Atomic Energy Commission (now known as the Nuclear Regulatory Commission), was designed to estimate the public risks involved in potential accidents at commercial nuclear reactors. Probabilistic risk assessment, when applied to nuclear reactors, seeks to identify all sequences of subsystem failures that may lead to a failure of the overall system; it then tries to estimate the consequences of each subsystem failure so identified. The result is a probability distribution, P(C): that is., the probability, P, per reactor year, of a consequence having magnitude C. Consequences include both material damage and health effects. Usually, the probability of accidents having large consequences is less than the probability of accidents having small consequences. A probabilistic risk assessment for a reactor requires two separate estimates: first, an estimate of the probability of each accident sequence; second, an estimate of the consequences-particularly the damage to human health-caused by the uncontrolled radioactive effluents released in the accident. An accident sequence is a series of equipment or human malfunc- tions, such as a pump that fails to start, a valve that does not close, or an oper- ator confusing an ON with an OFF signal. We have statistical data for many of these individual events; for example, enough valves have operated for enough years so that we can, at least in principle, make pretty good estimates of the probability of failure. Uncertainties still remain, however, because we can never be certain that we have identified every relevant sequence. Proof of the adequacy of proba- bilistic risk assessment must therefore await the accumulation of operating experience. For example, the median probability of a core melt in a light water reactor, according to the 1975 Rasmussen study, was I in every 20,000 reactor-years; the core melt at Three Mile Island's number two reactor (TMI- 2) occurred after only 700 reactor-years. The number two reactor, however, differed from the reactors Rasmussen studied, and in retrospect, one could rationalize most of the discrepancy between his estimate and the seemingly premature occurrence at TMI-2. Since the core melt at Three Mile Island. the world's light water reactors have accumulated some 1,500 reactor-years of operation without a core melt. This performance places an upper limit on the a priori estimate of the core- melt probability. Thus. if this probability were as high as I in every 1,000 reactor vears. the likelihood of su5iving 1,500 reactor-years would not be more than 22 percent; put otherwise, we can say with 78 percent confidence that the core-melt probability is not as high as I in 1,000 reactor years. With 500 light water reactors on line in the world, should we survive until the year 2000 without another core melt, we could then say with 95 percent confidence 62 ISSI!ES IN SCIENCE AND TECH'.OLOG1'

I n his essay "Risk, Science, and Democracy," William D. Ruckelshaus expresses very clearly what I call the regulator's dilemma. During the past 15 years. Ruckelshaus notes, there has been a shift in public emphasis from visible and demonstrable pollution problems, such as smog resulting from automobiles and raw sewage, to potential and largely invisible problems, such as the effects of low concentrations of toxic pollutants on human health. This shift is important for two reasons. First, it has changed the way that science is applied to practical questions of public health protection and environmental regulation. Second, it has raised difficult questions about managing chronic risks within the context of free and democratic institutions.z When the environmental concern was patent and obvious-such as the problem of smog in Los Angeles-science could and did provide unequivocal answers. Smog, for example, comes from the gas emissions from burning liquid hydrocarbons, and the answer to the smog problem lies in controlling these emissions. The regulator's course was rather straightforward because the science upon which regulatory decisions are made was operating well within its power. However, when the environmental concern is subtle-for example, how much cancer is caused by an increase of 10 percent in mean background radiation-science is being asked a question that lies beyond its power; the question is trans-scientific. Yet the regulator, by law, is expected to regulate even though science can hardly help him; this is the regulator's dilemma. Although my essay is subtitled The Regulator's Dilemma, many of the same issues anse in the adjudication of disputes over who is to blame and who is to be compensated for damage allegedly caused by rare events, such as nuclear accidents. The regulator's dilemma is also faced by the judge who is presiding over a tort case involving, for example, a claim for damages blamed on a toxic waste dump. Indeed, the regulator's dilemma could equally be called the toxic tort dilemma. A lawsuit involving alleged injury from chemical pollutants is unlike the traditional liability case. If my car injures a pedestrian, I am liable to be sued. What is at issue, however, is not whether I have injured a pedestrian. Rather, it is whether I am at fault. On the other hand, if the lead from my car's exhaust is alleged to cause bodily harm, the issue is not whether my car emitted the lead but whether the lead actually caused the alleged harm. The two situations are quite diffetent.. In the first example the relation between cause and injury is not at issue. In the second it is the issue. In this essay, therefore, I try to delineate more precisely those limits to sci- ence that give rise to the regulator's dilemma. I speculate on how these intrinsic limits to science seem to have catalyzed a profound attack on science by some sociologists and public-interest activists. In addition, I offer a few ideas that may help the harried regulators finesse these trans-scientific issues. I I Science deals with regularities in our experience; art deals with singularities. It is no wonder that science tends to lose its predictive or even explanatory power when the phenomena it deals with are singular, 60 ISSUES IN SCIENCE AND TECHNOLOGY

Ii. Supreme Qturt of the United States: Industrial Union Depanment, AFl: CIO v. American Petroleum Institute. et al., argued October 10. 19'9. dee:ided July 2. 1980. No. .'8-911. Washington, DC (1980). IG. Anierican Industrial Health Council: Q mment on: A Rep ut < f the GueraKenq- Regulatory Liaix>n Group Entitled ':ticientific Ba.u~ for Ielentif}•inK Potential Carcinogens and Estimating their Ri,k." AIHC. "iar.uLle. ( btay S. 19-9 ). 17. Purchase, LF.: Inter•,pecies Compari.xxts of Carcinogenicity. Br. J. Cancer 41:454-46K (19ki0). 18. l'.S. EmOronmerttal Protection Agency: Policy and Procedures for IdentiF<ing, and A,sessinR and Regulating Airtx)rne Substances Pc .tiinR a Risk of Cancer. Pr<tpu ecl Rule Fed. Reg. a4:5£3(i42 (19t30). Received 8 28r89: review decision 12/t/89; revision 2/8190; accepted 3/9/90 APPL OCCUP. ENVIRON. HYG. 5/8) • AUGUST 1990 517

Instead of asking science for answers to unanswerable questions, regulators should be content wa th less far-reach i ng answers. negotiation between individuals in conflict because they hold different non- scientific beliefs, how can one say that this scientist's opinion is preferable to that one's? Furthermore, if the matter at issue moves across the boundary between science and trans-science, where all we can say with certainty is that uncertainties are very large, how much less able are we to distinguish between the expert and the charlatan, between the scientist who tries to adhere to the usual norms of scientific behavior and the scientist who suppresses facts that conflict with his political, social, or moral preconceptions? One way to deal with these assaults on scientists and scientific truth would be to define a new branch of science, called regulatory science, in which the norms of scientific proof are less demanding than are the norms in ordinary science. I should think that a far more honest and straightforward way of dealing with the intrinsic inability of science to predict the occurrence of rare events is to concede this limitation and not to ask of science or scientists more than they are capable of providing. Instead of asking science for answers to unanswerable questions, regulators should be content with less far-reaching answers. For example, where the ranges of uncertainty can be established, regulate on the basis of uncertainty; where the ranges of uncer- tainty are so wide as to be meaningless, recast the question so that regulation does not depend on answers to the unanswerable. Furthermore, because these same limits apply to litigation, the legal system should recognize, much more explicitly than it has, that science and scientists often have little to say, probably much less than some scientific activists would admit. The expertise of scientific adversaries is often at the heart of litigation over personal injury alleged to be caused by subtle, low-level exposures. Each side presents witnesses whose scientific credentials it regards as impeccable. Because the issues themselves tend to be trans-scientific, one can hardly decide the validity of the assertions of either side's witnesses. Under the circumstances, I suppose, one is justified in regarding a scientific witness no differently than any other witness; his credibility is judged by his past record, behavior, and general demeanor, as well as the self-consistency of his testi- mony. Such, at least, was the way in which a federal district court judge, Patrick Kelley, settled Johnston v. United States, in which the issue was the claim that exposure to radiation from reworking old aircraft instrument dials had caused injury; Kelley impugned, on grounds no different from those one would invoke in an ordinary lawsuit, the competence if not the integrity of some of the plaintiffs scientific witnesses. VII There are various ways to provide some assurance of safety despite uncertainty. Here I briefly describe two of these ways-which I call the technological fix and de minimis-without claiming that these are the most important, let alone the only, ones. Technological fix. Science cannot exactly predict the probability of a serious accident in a light water reactor or the likelihood that a radioactive waste canister in a depository will dissolve and release radioactivity to the environment. Can one design reactors or waste canisters for which the 68 ISSUES IN SCIENCE AND TECHNOLOGY