Document jBzmpg3b8KzKEv43Z44pqo885

FILE NAME Brakes BRK DATE 1984 Nov 28 DOC BRK244 DOCUMENT DESCRIPTION AIA Comments to EPA Comments of the Asbestos Information Association North America Submitted to the U.S. Environmental Protection Agency on the Natural Resources Defense Council's Petition to Prohibit the Use of Asbestos in Brakes Nicholas J. Hluchyj Esq Assistant for Government Affairs November 28 1984 I. INTRODUCTION ; Information The Asbestos __._ Information Assooration Assooration North America a _ AIA , a profit organization whose member companies are involved in the mining manufacturing and marketing of asbestos and containing products in the United States and Canada wishes to comment on the petition to the Environmental Protection Agency filed under section 21 of the Toxic Substances Control Act TSCA by the Natural Resources Defense Council NRDC on September 13 1984. The petition requests that the Agency exercise its authority under section 6 of TSCA to prohibit the use of asbestos in brakes for new cars and trucks and in replacement brakes in existing vehi- cles In these comments AIA requests that the petition be denied for the following reasons 1 Ambient levels of asbestos and the small contribution of brake materials to those levels do not represent an unreasonable risk to the public 2 The use of containing products does not constitute an unreasonable risk to brake maintenance workers and in addition EPA should defer to the Occupational Safety and Health Administration on workplace regulation 3 Substituting materials for which the health effects have not been evaluated and whose use is uncontrolled for asbestos which is highly regulated could result in greater health risks to the public and workers 4 A ban would be contrary to the inter- national consensus on the controlled use of asbestos 5 The NRDC petition to ban the use of asbestos in brakes is not based on considerations of unreasonable risk as required by TSCA but rather on an approach which advocates a zero risk standard for the statute The discussion which follows will address each of these points in turn II The Use of Containing Brakes Does Not Constitute A Public Health Hazard In determining whether asbestos emissions from friction products pose a public health problem two distinct issues are raised 1 Do such emissions contribute significantly to the ambient level of asbestos 2 Are ambient asbestos concentrations a significant public health hazard If the answer to either question is no then can safely be concluded that no regulatory steps are necessary to reduce such emissions That is if friction product use does not contribute substantially to ambient exposure levels then attempts to reduce such emissions will not have a significant impact on any risk posed by such ambient concentrations Similarly if the ambient concentrations are not so high as to pose an unreasonable risk then regardless of the extent to which friction product emissions contribute to such levels they are not worthy of regulatory concern AIA is unaware of any substantial review that has concluded the ambient asbestos levels are worthy of regulatory concern In 1971 the National Academy of Sciences prepared a report collecting all available infor- mation on asbestos as an air pollutant In its Conclusion and Recommendations the NAS panel noted here are levels of inhaled asbestos without detectable risk It is not known what range of respirable airborne asbestos fibers will ultimately be found to have no measurable effects on health At present there is no evidence that the small numbers of fibers found in most members of the general population affect health or longevity The International Agency for Research on Cancer after sur- veying and evaluating all the available published literature on asbestos also concluded At the present time there is no evidence that exposure of the gener- al population to past levels of as- bestos dust in the ambient air or in beverages drinking food or pharmaceutical preparations increased the risk of cancer In 1977 after a thorough review of the available data a working group of experts reported to the Commission of the European Communities here is no established evidence that true ambient exposure through air water drugs beverages food as prevalent in Western European countries at this moment carries ... a definite health risk however there exist too many uncertainties to deny such a risk though if the risk was substantial it is likely it would have been detected by now Finally the United Kingdom's 1979 Simpson Report concluded here is no quantitative evidence of a risk to the general public from ex- posure to asbestos dust It is concluded that the presence of chrysotile alone or contaminated with small quantities of amphiboles is unlikely to have produced any material increase in the risk of lung cancer in the general population or any appre- ciable number of cases of mesothelioma The same is certainly true of asbestosis In short the uniform opinion of these respected authorities each of which has investigated the issue in depth is that there is no evidence indicating exposure to asbestos in the ambient environment poses a public health problem This consensus that ambient concentrations of asbes- tos pose no public health hazard of any significance establishes a framework within which to ask more particular questions about friction product emissions In light of the expert opinion it is unlikely that any problem exists Nonetheless review of the evidence is useful to confirm that conclusion Determination of the extent to which friction product emissions contribute to ambient asbestos concentrations re- quires data on four different issues 1. How much asbestos is worn away from brakes and clutches through use of these friction products 2. 2. What percentage of the asbestos material that is worn is emitted in the form of asbestos fibers 3. What percentage of the emitted asbestos fibers become airborne thus contribu- ting to ambient concentrations 4. To what extent do the emitted airborne asbestos fibers contribute to ambient concentrations As the following discussion highlights experts who have analyzed these four questions have reached general agreement on questions 1 and 3. The only dispute in the data collected occurs with respect to question 2 and there is general consensus all but one study Differing methodologies have been employed to answer question number 4 1. Asbestos Wear It was generally agreed in the early and 1970's that approximately 35,000 tons of asbestos were being worn annually from brakes and clutches That amount was originally calculated by investigators from the Bendix Corporation led by Michael Jacko The 1973 Bendix estimate was based on an assumption that of the annual amount of friction material then being installed on automobiles trucks trailers and buses 171 million pounds 25 or 43 million pounds was discarded at the time of relining i.e. not worn off and another smaller percentage 11.7 million pounds was discarded when the vehicles were junked leading to a remaining 117 million pounds that were worn away annually As approximately 60 of this friction material was asbestos the investigators concluded that approximately 74 million pounds or 37,000 tons of asbestos were being worn 2. Percentage of Wear Which Is Asbestos Fiber Several studies have been conducted to determine the percentage of asbestos friction material wear that is emitted in the form of asbestos fibers Such studies are necessary because chemical and physical changes occurring in the braking process cause a large percentage of the debris not to be emitted in the form of asbestos fibers Under high temperatures chrysotile asbestos undergoes dehydroxylation and recrystalization resulting in fibrous forsterite or olivine Forsterite will form only from pure asbestos making it more likely that olivine will be found in brake debris and explaining why some observers did not detect forsterite in their samples That friction wear dust is qualitatively different from asbestos in terms of potential health effects has been demonstrated in a number of studies For example Davis and Coniam 1973 found very low fibrogencity for automobile brake lining dust as compared to studies with native fibers in mouse injection studies Similarly the study of LeBouffant et al 1983 showed that chrysotile heated to 700 as occurs in braking loses its tumorigenic potency by intrapleural adminis- tration The most extensive and designed study of friction material wear was conducted by The Bendix Corp. under contract with and in cooperation with EPA Through the speocfispa ecil al equipment attached to brakes and clutches to capture emissions in actual use the inves- tigators were able to obtain data from actual driving con- ditions Both typical and more abusive driving conditions were tested using both original and aftermarket equipment for both disc and drum brakes from five different manu- facturers testing More than 8,000 miles were driven during the The collected wear debris were analyzed by both optical and transmission electron microscopy Some samples were independently analyzed by Batelle Columbus Laboratories whose results were slightly lower than those of Bendix The Bendix study found that very small percentages well below % by weight -- of brake debris were asbestos Vehicle Test Range Overall Average 3 .003 - .518 .078 .20 .20 Similarly small percentages of brake wear that were asbestos fibers were also found by several other investigators -8 in studies under simulated driving conditions One of earliest studies was conducted by the U.S. Department Health Education and Welfare in the late 1960's Je R. Lynch tested and clutches on 15 different automobile truck and bu friction testing machines and dynamom under various conditions to determine the percentage fibers in the emitted material Lynch also reported less than % of brake wear was asbestos fibers Company streams tests in the early 1970's by Fo Dynamometer yield comparable results Anderson et al 1 in front of and behind a disc brake assembly under break normal us a dynamometer were sampled temperature conditions Fibers were measured by tr electron microscopy _ The multiplied by a factor of Ford findings ten to account each of wh for possib and counting were also we in collection processing Asbestos fiber from brake in airborne wear dust Asbestos wear fiber released from lining that less than % of friction ma Findings asbestos fiber were also reached in two British st debris from stationary brakes were analyzed Hick Knight 1970 Hatch 1970 It was stationary brake study conducted by only in one c the Mount Sir values were found tal researchers that higher study Rohl et al 1976 reported that they ob samples of automobile brake drum dusts and exami by optical microscopy ray diffraction and transmission and scanning electron microscopy No details of the collection or analytic procedures nor the rationale for choosing the particular 10 automobiles are provided Only overall results are reported Asbestos fibers were found to constitute % to 15 of the weight with an average of 38 to 68 The two most recent studies to examine asbestos brake emissions neither of which are cited in the NRDC petition are in accord with the earlier studies which demonstrated a very low content of asbestos in brake dust Williams and Muhlbairer 1982 concluded that over 99.99 of the mass of original asbestos fibers was broken down into nonfibrous magnesium silicates Similarly Cha et al 1983 reported that their analysis of brake dust agreed well with the WillofiWa illmias ms and Muhlbaier 1982 finding that the dust only averaged an asbestos content of 0.018 - In sum only one emissiontso be more than study has found friction product wear 18 asbestos by weight That study was conducted by analyzing dust in stationary brakes rather than through collection from brakes and clutches in use Considerable questions arise about its inordinately high values and their re- lation to actual use emissions The totality of the evidence would indicate that less than % of friction product wear i.e. less than 350 tons annually is asbestos fiber 3. The Disposition of Emitted Fibers All emitted fibers from friction product wear do not become airborne Many will re- main in the friction mechanism others will settle to the earth The most extensive testing to determine what percentage of emitted fibers become airborne was done as part of the Bendix study In the Bendix study three brake emissions collectors were used with the sump collecting debris that normally would remain trapped in the brake the surface collecting debris that would normally drop to the road and the airborne filters collecting the debris that become airborne The weight of the asbestos fibers in each test of each type brake was determined for all three final resting places Based on model of the braking ex- periences that a typical automobile would encounter during its life and using the automobile test vehicle data from the study the investigators were able to calculate the percentage of all asbestos fiber wear that would be deposited in each of the three possible locations Road Dropout Airborne Retained in brake 81.9 3.78 14.4 Less than % of the fibers were estimated to be airborne for trucks so that an overall figure of 3.2 airborne was calculated for all vehicles 4. Friction Material Emission As a Contribution to Ambient Concentrations In the NRDC petition there is men- tion that 158,000 pounds of asbestos are released into the atmosphere each year from the normal braking process of automobiles This figure quoted in the petition is taken from the study prepared by M.G. Jacko and R. T. DuCharme for EPA in 1973 contract 68-04-0020 and published by the Agency as document No 222 372 A condensed version of this report was also published in Society of Automotive Engineers Vol 18 May 14-18 1973. The authors of the petition however failed to quote the entire paragraph in the EPA report which says 10.5 SUMMARY OF ASBESTOS EMISSIONS The results indicate that more than 99.7 percent of the asbestos used in friction material is converted to a fibril form The total as- bestos emissions for all vehicles in the United States ally remain is estimated to be 158,000 pounds annuOf this total a small part was found to airborne The contribution to the atmos- phere is estimated to be 5060 pounds or 3.2 percent of the total asbestos emissions It is therefore clear that according to the cited study the contribution of asbestos to the atmosphere from braking is 5 060 pounds and not 158,000 pounds More recent studies have also calculated the contri- bution of brake dust emissions to the ambient atmosphere Williams and Muhlbaier 1982 concluded that an expected urban concentration due to braking of 0.063 mcan be predicted This is small fraction 0.06 to 0.5 of the measured urban asbestos concentrations of 10-100 mNicholson et al 1971 The results of the study of Cha et al 1983 are again in accord finding that application of the asbestos emission rates to air quality models confirmed Williams and Muhlbaier's finding that about 1 of asbestos fibers in city core districts originated from disc brake wear The cited studies in sum amply demonstrate that the contribution of brake dust emissions to ambient levels of asbestos is not significant and certainly cannot be interpreted as constituting an unreasonable risk to the general public III Asbestos and Automobile Maintenance Workers The NRDC also claims in its petition that automobile maintenance workers are at a particular risk from exposure to asbestos brake products This claim is based upon a calculation predicting the excess risk of various populations occupationally exposed to asbestos Nicholson et al 1982 The calculations for different occupationally exposed groups are made by extrapolating from a study of insulation workers Selikoff et al 1979 for which no exposure data exists The claimed number of excess deaths are therefore the result of a highly technical and subjective series of infer- ences and should not be used as the basis for a finding of unreasonable risk under TSCA The problem of estimating risks by extrapolating from studies which lack exposure data was recently emphasized in comments from the Environmental Health Committee of EPA's Science Advisory Board addressed to Administrator William D. Ruckelshaus After reviewing a draft document entitled As- bestos Health Assesment Update prepared by the Office of Health and Environmental Assessment in EPA's Office of Re- search and Development the Committee made the following ob- servations with regard to exposure data use in the draft The document gives greater weight in deriving a risk value to studies in which individual exposures were not estimated In fact epidemiologic studies are available in which individual exposures are estimated In addition the distribution of samples at a site generally adhere well to a normal distribution The document however uses pooled samples from all sites which assumes a similarity of sites and sources These differences need to be emphasized for the regulator because any statistical bias in the description of the past incidents in which asbes- tos exposure was associated with health effects will be replicated in the prospective estimates of risk used in regulating Such concerns indicate that at the very least extrapola- tions of risk based on studies for which exposure data does not exist should be evaluated very carefully and not be accepted at face value for the purpose of issuing regulations A study more on point actually examining a cohort of brake lining repair and maintenance workers occupationally exposed to asbestos failed to demonstrate any significant or unreasonable risk Nicholson et al undated Among the relevant conclusions in this study were 1 A greater prevalence of ray abnor- malities is found among garage mechanics who repaired brakes than among blue collar controls or garage workers who do not engage in brake or auto body work Note that this conclusion is confounded by the inclusion of auto body workers 2 The pulmonary function results of garage mechanics engaged in brake work are no different from non- garage workers and other general population controls Such modest observations can hardly support a finding of un- reasonable risk Additional evidence of the small risk to workers from containing brakes or other friction materials is present in the recently published study of Berry and New- house 1983. In that study the mortality experience of 13,460 workers over nearly forty years in a factory manu- facturing friction materials was analysed Although the ex- posure levels of these workers were many times higher than the exposures of brake cluded maintenance workers the study con- - 15- There was no evidence of an overall increase in mortality or of any excess of deaths due to lung cancer either in relation to the national population or within the factory population to different levels of exposure There was also no convincing evidence of excess mortality from gastroin- testinal tumours either in the main mortality study or in the control study Of 11 workers dying of mesothelioma in the study eight worked on the con- tract in which crocidolite was used and another exposure to may have had crocidolite intermittent Crocidolite is not used in the manu- facture of friction materials An even more recent study that of McDonald et al 1984 of an American asbestos friction products plant produced similar results with the exception that no mesotheliomas were detected To summarise if we accept that the high mortality from all causes including respiratory cancer in men employed for less than one year was probably due to some form of selection our results sug- gest that the adverse health effects of employment in this chrysotile friction products plant were small In our plant no amphibole asbestos was used until after 1957 anthophyllite) and no mesothelioma was found Again the above studies indicate that even under the much higher exposure circumstances compared to brake maintenance workers found in the past in the manufacture of containing friction materials the risk is small However the NRDC petition urges the EPA to ban the use of asbestos in brakes on the basis of this occupational risk Besides not being supported by the available evidence such an action would encroach upon the rulemaking activities of the Occupational Safety and Health Administration OSHA, the agency with primary responsibility for the regulation of workplaces and occupational risks Earlier this year OSHA proposed to revise the workplace standard for asbestos and in June and July held five weeks of hearings which extensively addressed the issue of occupational asbestos exposure A new standard is expected to be issued in 1985. The record developed during the OSHA proceeding establishes that the revised standard supported by AIA will eliminate any remaining significant risks in the occupational setting Were OSHA to accept recommendations made by AIA the revised asbestos standard would be the tightest of any country in the world While it may never be possible to prove that such low exposures are absolutely safe any reason- able assessment of the risk remaining at such low levels will show that such risks are far lower than countless other risks commonplace in many workplaces today The NRDC petition in large part requests that EPA address this very same issue Whether or not EPA has legal authority to regulate occupational risks and AIA believes 17 it does not it makes little sense for two government to conduct lengthy rulemakings on the same subject agencies IV A Ban on Asbestos Would Lead to the Uncontrolled UGsreeaotferSuHbesatlitthutReissk Which May Present A substitutes cites the availability of The petition which to prohibit its use in for asbestos as a basis on brakes While addressing to a limited extent aspects of materials which substitution the petition make them suitable fails to raise the the technical candidates for issue of the health risks of substitutes that the health effects It is commonly recognized be closely related to the physical of asbestos appear to Asbestos itself is only a characteristics of fibers and regulatory usage which term based on commercial generic different mineral fibers The evidence is applies to six naturally occuring or man suggestive that any fibers very a health similar physical properties present made that have risk study undertaken by the A very recently published National Academy of addresses this very Sciences NAS at the request of the EPA issue its findings on the In summarizing to health effects the relationship of fiber characteristics NAS report entitled Asbestiform Fibers Nonoccupational Health Risks listed the following factors in approximately descending order of the strength of the positive evidence Respirability For significant health effects to result from inhalation of asbestiform fibers the fibers must reach the lower portions of the respiratory tract where they cause the most damage Although the limiting upper diameter appears to be about 3 um fibers that are much longer than wide can penetrate deeply in the respiratory tract Length Diameter and Aspect Ratio i.e. Ratio of Length to Diameter Experiments inducing mesothelioma in rodents by injections of test material have indicated that long thin fibers yield more tumors than do short thick fibers Samples with an overwhelming majority of fibers shorter than 5 um yielded mesothelioma in rats when injected intraperitoneally but the pathogenic role of short fibers especially those shorter than 3 um is unclear Fibers longer than approximately 10 um cannot be completely en- gulfed and inactivated by macrophages and they have tended to produce more disease in animal tests than have the shorter fibers Other Properties The number of fibers which is also correlated with surface area generally appears to be a more relevant measure than mass in determing pathogenicity Durability also appears to be a factor The more durable fibers appear to be more pathogenic in some studies than fibers that are less durable The relevance of fiber surface charge to effects on human health remains to be demonstrated Some experimental studies have indicated that surface charge appears to be involved in cytotoxicity Although chemical composition is related to physical properties of asbestiform fibers a direct role for chemical composition per se in biological activity has not been demon- strated Considering what is already known concerning the potential health effects of fibers generally the NRDC petition's advocacy on behalf of the uncontrolled use of aramid or other fibers in brakes in place of the controlled use of asbestos takes on an air of rashness The health benefits if any to be derived from such a course of action must be viewed skeptically in light of what is presently known Similarly the effects of a wholesale switchover to metallic brakes must be given far more thoughtful consideration Metals are known to posses a carcingenic potential what are the effects of occupational and environmental exposure to respirable particulates from metallic brake dust Until an answer can be formulated to this question indiscriminate substitution of metallic brakes for asbescontaining brakes should not be endorsed much less required by a government agency charged with protecting public health and the environment V. A Ban Would Be Contrary to the International Consensus on the Controlled Use Approactho the Regulation of Asbestos That an international consensus exists favoring the regulatory approach of controlled use as oppossed to a ban on the use of asbestos was vividly illustrated following the announcement by EPA last year that it planned to issue proposals calling for the immediate ban of certain containing products and a more gradual phase of remaining asbestos uses Diplomatic notes opposing EPA's regulatory approach were forwarded from Canada the European Economic Community EEC the United Kingdom Belgium the Federal Republic of Germany Austria Switzerland and Mexico In a speech delivered in December 1983 Canadian Ambassador to the United States Allan Gotlieb noted Nations that make up the European Economic Community have concluded on the basis of a lengthy review by international experts that properly regulated and labeled asbes- tos used at minimal exposure levels poses no undue risk This position has the support of the International Labor Organization A group of experts comprised of industry labour and government representatives developed a code of practice for the safe use of asbestos which is gener- ally consistent with the approach of the EEC This unfavorable international reaction prompted the EPA to conduct a poll through the State Department to determine whether any nations supported its plans Only Denmark of all the responding nations supported the EPA approach see Inside EPA at 5 August 31 1984 Ironically Denmark is the first nation to have taken regulatory action to address one of the mosi serious flaws in a ban approach It has established an fiber regulatory. - 21 - standard to assure that any fiber use is closely controlled The growing international awareness and consensus on the potential dangers resulting from the uncontrolled use of substitutes is echoed as well in the positions taken on this issue by responsible parties in the United States The U.S. Department of Labor has recently joined the many na- tions who have concluded bans are unwarranted In the De- partment's official comments to an ILO questionnaire on asbestos the Department wrote While continued use of asbestos may be curtailed where suitable substitutes are available it should still be recognized that with appropriate pro- tective measures asbestos is still a valuable resource With regard to the replacement or substitution of asbestos by harmless or less harmful substances it should not be presumed that any sub- stitute will be harmless or less harm- ful Rather each potential substitute should be thoroughly evaluated The CIO's comments to the same ILO questionnaire agree that any ctions to require or encourage the substitution of asbestos must include a full evaluation of the toxicity of the substitute materials and regulation of these materials as necessary It is amply evident that the great majority of expert world opinion favors the approach of the controlled use of asbestos as oppossed to a ban and the resulting in- crease in the unregulated use of substitute materials whose health effects have not been evaluated VI The NRDC Petition Would Require the Application of Zero Risk Standard Rather Than the Unreasonable Risk Standard Required by TSCA While acknowledging that TSCA requires a determination of unreasonable risk as the basis for regulatory action by the EPA the NRDC petition is essentially premised upon a no safe threshold or zero risk approach The petition asserts that no safe threshold levels of exposure to asbestos can be established and again that it is currently impossible to set a safe level for ex- posure to asbestos Such assertions while useful within the context of theoretical exercises such as the extrapolation of risk from high to low levels of exposure become meaningless as guides for practical action A claim of no safe threshold or no safe level of exposure is at base a declaration of the obvious clothed in sinister garb Limiting the proposition to the population of the United States at the pre- sent time no safe threshold means there can be no guarantee of the total absence of any adverse effect in a popu- lation of approximately 230 million people How many guarantees of absolute safety can be made concerning any sub- stance: attempts attempts attempts paralyzed self self ach. taken taken flawed projections Education substitutes substitutes substitutes brakes such itit prakes prepared - susuch " in the as the discredited disavowed disavowed the U.S. Department , of byby facile discussion Health - and its in 1978 asbestos asbestos use of must denied based on as risk approach a zero in approach . scope ofac- the - absence further risk controlled evidenced evidenced use evidenced che environment in inter- jnter- opposed questionable asbestos asbestos benefits of banning questionable questionable for ference benefits fe) national pre che <unregu- unregu^' of asbestos: panning lated use of substitutes and the social and statutory rejection of a zero risk approach to regulation should lead to the denial of the NRDC petition - 25 REFERENCES CIO 1984 Responses of the CIO to ILO Questionnaire on Asbestos October 29 Anderson A. E. et al ( Dynamometer Tests May 14-18 1973 Asbestos Emissions from Brake Society of Automotive Engineers a Berry G. Newhouse M.L. 1983 Mortality of Workers Manufacturing Friction Materials Using Asbestos Br J. Ind Med 40 Bridbord K. et al 1978 Estimates of the Fraction of Cancer in the United States Related to Occupational Factors U.S. Department of Health Education and Welfare Washington D.C. British Advisory Committee Report 1979 Asbestos The Simpson Cha S. et al 1983 Simulation of Automobile Brake Wear Dynamics and Estimation of Emissions SAE Technical Paper Series No. 831036 June 6-9 Commission of the European Communities 1977 Public Health Risks of Exposure to Asbestos - Davis J. M. G. Coniam S.W. 1973 Experimental Studies on the Effects of Heated Chrysotile Asbestos and Automobile Brake Lining Dust Injected into the Body Cavities of Mice Exper Molec Path 339 Environmental Health Committee Science Advisory Board U.S. Environmental Protection Agency 1984 Letter to Honorable William D. Ruckelshaus Administrator U.S. Environmental Protection Agency October 29 Gotlieb Allan Meeting 1983 Speech delivered to AIA Director's December 13 . Hatch D. 1970 Possible Alternatives to Asbestos as a Friction Material Ann Occup Hyg 13:25 Hickish D.E. Knight K.L. 1970 Exposure During Brake Maintenance Ann Occup to Asbestos Hyg 13:17 IARC 1973 Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man Vol 2 Inside EPA August 31 1984 Jacko M.G. Ducharme R.T. Somers J.H. 1973 Brake and Clutch Emissions Generated During Operation Society of Automotive Engineers May 14-18 Vehicle Jacko M.G. et al 1973 Brake Emissions Emission Measurements from Brake and Clutch Linings from Selected Mobile Sources EPA Report 222 372 LeBouffant L. et al 1983 Influence d'un traitement thermique des fibres de chrysotile sur leur comportement dans le poumon Pollution Atmos- pherique Jan. - Mar. 44 Lynch J.R. 1968 Brake Lining Decomposition Products J. Air Poll Control Assn 824 McDonald A.D. et al 1984 Dust Exposure and Mortality in an American Chrysotile Asbestos Friction Products Plant Br J. Ind Med 151 National Academy of Sciences National Research Council 1984 Asbestiform Fibers Nonoccupational Health Risks National Academy Press Washington D.C. Nicholson W. J. et al 1971 Asbestos Air Pollution in New York City In Proceedings of the Second International Clean Air Congress Academic Press New York Nicholson W. J. et al 1982 Occupational Exposure to Asbestos Population at Risk and Projected Mortality -- 1980-2030 Am J. Ind Med 259 Nicholson W. J. et al Undated Investigation of Health Hazards in Brake Lining Repair and Maintenance Workers Occupationally Exposed to Asbestos NIOSH Contract 210-77-0119 Rohl A. N. et al 1976 Asbestos Exposure During Brake Lining Maintenance and Repair Env Res 110 U.S. Department of Labor 1984 U.S. Government Response to Questionnaire Report VI 1 - Safety in the Use of Asbestos October 29 Williams R. L. Muhlbaier J. L. 1982 Emissions Env Res 29:70 Asbestos Brake