Document 5kYV1nr6dMXywaRB8dD0M5E90

AppliedOccupationslandEnvlroimtmialHygiene, Copyright AppliedindustrialHygiene ISSN: 1047-322X print /1521-0898 online DOI: 10.1080/10473220390229240 18:786-804.2003 An Evaluation of the Historical Exposures of Mechanics to Asbestos in Brake Dust Dennis J. Paustenbach, Richard O. Richter, Brent L. Finley, and Patrick J. Sheehan Exponent,Oakland,California This article presents a historical analysis of published data regarding the exposure of brake mechanics to asbestos as a result of doing brake work. Concerns about this possi ble hazard were first raised in the late 1960s. This analysis focuses on 30 years of data collected during the brake re pair event (e.g., a brakejob) and 8-hour time-weighted aver age (TWA) personal samples. A brake job TWA represents the average concentration a mechanic experienced during brakeservicing, rather than throughout the workday, and an 8-hour TWA represents the average.airbome concentration of asbestos for the entire workday (which would involve brake work and other activities). Nearly 200 brake job and 8-hour TWA airborne asbestos samples were analyzed to assess how asbestos concentrations varied by type of vehi cle serviced, country in which mechanics worked, time period^ndbrake-deaningmetbod.Tofacilitatecomparisons, brake job TWAs were converted to estimated 8-hour TWAs using the durations and number ofbrakejobs performed per mechanic each day. Estimated and measured 8-hour TWAs for mechanics servicing automobiles and light trucks ranged from<0.002to0.68r/cc,withameanofdi.04f/cc.Incontrast, the 8-hotur TWAs for mechanics servicing heavy trucks and buses ranged from 0.002 to 1.75 f/cc, with a mean of 0.2 f/cc, siiggestingtbatthesemechanicsexperiencedhigherdailyasbestos exposures than automobile and light truck mechanics. Brakejob and 8-hourTWAs for brake mechanics worldwide were found to be similar during the same time periods, and they were consistently below contemporaneous occupational health standards in the United States. The increased use of brake-dust control measures in some garages resulted in at least a 10-fold decrease in the TWA airborne concentrations of asbestos from the 1970s to the late 1980s. Keywords Asbestos, Industrial Hygiene, Auto Mechanics. Brake Dust,Exposure,OccupationalHealth Asbestos has been used in automobile brake linings worldwidesmcetheearlyl900sbecauseithassuperiorpeiformance characteristics/1* Itwasnotuntilthel960s,however,thatconcems arose regarding the potentialhealth hazard associated with exposure to airborne asbestos resulting from automobile brakes. Thomson etal.p* werethefustresearcherstoaddressthepotential impact ofemissions from thebrake linings ofvehicles during braking on ambient air concentrations of asbestos. Specifically, Thomson0* observedseveral cases ofmesothelioma (a rare form ofcanceras$ociatedwithasbestosexposure)inSouthAfricans whohadnohistoryofoccupationalorotherexposuretoasbestos andfoundunexplainedasbestosbodiesinroutinehistological sections oflungs collectedduring autopsies. Based on these find ings, he concluded that these individuals were likely exposed to asbestos products in their homes or to asbestos in ambient air from brake lining wear during vehicle braking, or from disin tegration by natural weathering of asbestos-containing building materials.0* The question raised by Thomson prompted a number ofstudiesonthepotentialimpactofasbestosemisstonsfrombrakeliningsonambientairquality.Thesestudies. (4_8* provided data on anumberoffactors,inciuding(l)theamountofasbestosinthe weardebrisdustfromautomobilebraking,(2)thesizcdistribution ofobserved fibers, (3) the quantities ofasbestos emitted into ambient air from vehicle braking, and (4) the resulting estimated ambientairconcentration.Animpoitantfindiiigofihesestudies was that the asbestos content in brake dust ranged from 0.02 to < 1 percent,therebyconfimungthehypothesisthatmostofthe asbestos in the original lining material (which was composed of about 35% to 65% asbestos) was thermally degraded during braking.However.noneofthesestudiesspecificailyaddressed potential asbestos exposures of mechanics servicing brakes. The first investigation of airborne asbestos in a brake re pair garage was undertaken by Hickish and Knight0* in the late 3960s.ThisstudywasconductedataForddealeishipinLondon, apparentlytoevaIuatecompliancewiththe]968BritishOccupationalHygieneStandardforChrysotileAsbestosDust. <l0> Soon thereafter, in 1971, similar studies were conducted in the United States, following the promulgation of an occupational standard forasbestosbytheOccupationalSafetyandHealthAdministration (OSHA). From 1972 through 1989, the National Institute 786 HWBUI0009522 EXPOSURE OF MECHANICS TO ASBESTOS 787 for Occupational Safety and Health (NIOSH) conducted numerousinvestigationsofvehiclebrakeservicingoperationsinthe UnitedStates. <l,l,~'u* Inaddition,independentstudiesofairbome asbestos levels in brake-servicing garages were published in the 1980s and 1990s by researchers in the United States/1 Germany/17* Sweden/18* andAustralia.(l9) Despite the number of studies conducted over the past sev eral decades, there has been no apparent attempt to use all of the available published air monitoring data to characterize historicalexposurestoasbestosfrombrakesforbrakeniechanics under various working conditions. In this article, the measured airbomeasbestosconcentrationsfrompublishedsurveysofvehicle brake repairfacilities were presented and evaluated to char acterize historical exposures for brake mechanics under various woridngconditions.Theconcentrationsrepoitedfonnechanics servidngbrakeswerecharacterizedandcomparedbasedonthe periodwhen sampling was conducted, where it was done (United States and overseas), the types of cleaning methods used, arid thesizesofthevehicles(carsandlighttnicksorheavytmcks and buses). The data were then used to estimate die distributionsofdailyairbomeconcentrationsforbrakemechanicswho performed brake repair work in the 1960s and 1970s, and more recentlyinthel980sandl990s.Finally,estimated8-hoinTWA concentrationsexperiencedbybrakemechanicswerecompared to occupational permissible exposure limits (PELs). METHODS PublishedstudiesffomtheUnitedStatesandabroadthatpro- vided long-term personal air sampling data on asbestos conccntrationsexperiencedbymechanicsduringbrakeservicing operationswereevaluated.Generally,onlysampleswithsamplingdurationslongerthanl hourwereincluded.Short-term samplescollectedduringblow-outonelated "peak exposure events" were not considered informative for.assessing the health hazardtomechanicSWithoutimnsideringtiine/motibninfonna- . tion; however, the impacts of peak exposures are captured by thelongerrfermsampIingevaluatedhere.Basedorithesecriteria,1Ostudieswereidenti fied/1,9:12-.1?* ' . In the studies evaluated, personal air samples were collected on filtersinthebreathingzonesofthemechanics.eitherduring the brake servicing operations or throughout the mechan ics' workdays: All of the samples were analyzed for asbestos fibers greater than 5 micrometers (pan) in length and with at least a 3-to-l length-to-width ratio, (called an aspect ratio) using Table I, slightly different sampling and analysis methods*20^23* wereusedtoquantifyairbomeasbestosconcentrationsinthese studies, the reported methods are sufficiently similar that the data arecomparableandrepresentativeoftherangeofairbomeasbestos concentrations that mechanics likely encountered during brake servicing operations in various countries and eras. MeasurementsreportedinthelOstudiesweregenerallyexpressed as time-weighted average (TWA) airborne concentra tions of asbestos for mechanics as they performed one or sev eral brake services (i.e., "brake job TW\s"),orasaveragedaily concentrations of asbestos for individual mechanics as they per formed various activities throughout the course of their day (i.e., "8-hour TWAs"). Unless specificaliyieferxedtoinareportas 8-hour TWAs, it was assumed that the data collected were for brake job TWAs. This assumption could usually be confirmed by examining the duration of the sampling event Table 1 summarizes the 10 published studies that we could identifythatprovidedataonairbomeasbestosconcentrations formechanicsservicingcar,truck,andbusbrakes.Together, overthepast30years,theconcentrationsofairbomeasbestos in the breathing zones of mechanics have been measured in 53 brake repair facilities in the United States, 76 facilities in Germany, 23 facilities in Sweden, 4 facilities in Australia, and 1 facility in the United Kingdom. The reported brake job and 8-hour TWA concentrations for toe mechanics in all of these studiesaiepresentedinTablellforautompbileandlightbuck . mechanics and in Table III for heavy truck and bus mechanics. In the studies by Rodelspergeretal. (17) and Moore/1* the sampling data were not available; only the mean asbestos concehtrationsformultiplemechanicsdoingvarioustypesofbrake servicing activities were reported, rather than the results for in dividual mechanics. We did, however, attempt to obtain their originaldata.'Althoughitisnotpossibletousetheirsummary information in this statistical analysis of TWA concentrations, the mean concentrations that they measured can be compared toexposuresariipngbrakemechanicsduringrelevanttimeperiodsihthevariouscountrieswheresampIeswerecolIected.The studiesevaluatedaresummarizedinthefollowingsections. United Kingdom Study The firstpublishedstudy ofoccupational exposure to airborne asbestos due to brake dust was carried out in 1968 at a Ford dealershipinLondon. *** Likely prompted by the then-new 1968 British standards for asbestos in the workplace, Hickish and Knighti9* estimated the exposure of a mechanic engaged in toe.. removal of brake dust from a brake drum using compressed air dunnganentirewoifoWffduringwhich 11 carswereserviced. No other study has ever reported that a single mechanic worked onsomanyvehiclesduringasingleday.(Even2 -3 brakejobs per day is high for a single person in a brake shop.) The measured 8-hour TWA concentration for this mechanic, 0.68 fibers per cubiccentimeter(f/cc),isthehighestreportedvalueforany . mechanicservicingcarbrakesinanyofthesubsequentstudies thatwereconducted.Theseresearchefsalsoreportedan8-hour TWA of 1.75 f/cc for a mechanic servicing truck brakes, which, again.isthehighestreportedvaluefortruckandbusmechanics servicing brakes encountered in a review of the literature. United States NIOSH Studies Between 1976 and 1989, researchers at NIOSH collected personal samples for 75 mechanics in 22 settings, including commercial brake and front-end repair shops, fleetservice ) HWBUI0009523 788 D. j. paustenbAch et al. TABLE1 Pub!ishedindustnaIhygienestudieswithtime-weightedaverage(TWA)asbestosconcentrationsfonnechanicsservicingcar, bus.andtruckbrakes Type of facility Number Number Number Personal mechanics mechanics brake samples employed evaluated jobs/week collected . Reported TWA values TWA durations (hours) Study Method Service bay Ford dealer Fleet service garage Brake/foont-end Brake/ront-end Brake/front-end Largs brake service (1976) Large brake service (1977) Brake/foom-end/muffler Track brake maintenance (1976) Track brake maintenance (1977) Commercial brake Brabs/fnsM-end Biake/front-end Large brake service Municipal garage Municipal garage Municipal garage Fleet service garage 76 garages Germany NR 3 3 3 3 5 5 3 .7 7 5 NR 3 5 60 5 3 4 NR 1 1 1 1 1 4 3- 2 3 3 2 1 1 3 2 3 1 1 NR 11/day 2-5 10-14 4-6 20-30 35-45 35-45 4-5 NR Nft 35-40 NR 4-6 35-40 40 1 NR 1/shift NR 6 l daily 3 I brake job 2 1 brakejob 3 1 brake job 7 2 brakejobs 16 4 brake jobs 8.0 5.7 7.9 5.9 1.5,3.0 4.7-7.7 (9) (12) (12) (12) (12) (12) BOHS (1968) OSHA/NIOSH OSHA/NIOSH OSHA/NIOSH OSHA/NIOSH OSHA/NIOSH 45 15 brake jobs NR (12) OSHA/NIOSH 2 2 brake jobs 9 2 brakejobs 1.6,3.0 (12) OSHA/NIOSH 43,5.0 (12) OSHA/NIOSH 6 3 brakejobs 23-6.4 (12) OSHA/NIOSH 5 2 brakejobs 6.2,6.2 (14) OSHA/NIOSH 2 1 brakejob 4.3 (13) OSHA/NIOSH 4 4 brakejobs 43-5.9 (15) OSHA/NIOSH 2 2 brakejobs 4.7,5.7 (15) OSHA/NIOSH 2 2 brake jobs 3.3,5.0 (15) OSHA/NIOSH 3 3 brake jobs 2.3-6.2 (15) OSHA/NIOSH 1 1 brakejob 5.4 (15) OSHA/NIOSH 1 1 brakejob 4.0 (15) OSHA/NIOSH 67 Mean NR (17) AIA (1979) "combination" 31 garages United States Government maintenance Postal maintenance Fleet service garage Postal maintenance Private utility garages Outdoors Service station Garages Sweden Garage Australia Garage Australia Garage Australia Bus service depot Australia NR 6 a 2 to . 5 1A .t NR NR NR NR NR Note. NR--notreported. ADo-it-youraelfraeehanic. NR NR NR NR NR NR 1A 1 NR 1 1 1 1 NR 6-10 28-36 1 6 7-9 NR. NR NR 20 4 42 35 Mean brake job 0.2-1.0 (16) MF-PCM (400x) 18 9 brakejobs 2.0 (31) OSHA/NIOSH 22 11 brake jobs 2.0 (31) OSHA/NIOSH 13 7 brakejobs 2.0 (31) OSHA/NIOSH 20 10 brake jobs 2.0 (31) OSHA/NIOSH 8 4 brakejobs 2.0 (31) OSHA/NIOSH 2 1 brakejob 2.0 (31) OSHA/NIOSH 2 1 brakejob 2.0 (31) OSHA/NIOSH 23 23 8-hour. 8,0 (18) NR 1 1 brake job 1.3 (19) NOHSC (1988) 1 I brake job 1.3 (19) NOHSC (1988) 1 1 brakejob 2.2 (19) NOHSC (1988) 1 1 brake job 2.1 (19) NOHSC (1988) garages,tnjckbrakemainenaxicegarages,municipalgarages, private utility maintenance garages, one service station, and one drivewaysampleforado-it-yourselfmechanic. These evaluations were apparently prompted by the meet ing among NIOSH, researchers at Mt Sinai Hospital, and in dustry representatives, which was held in July I975/24' The NIOSH investigations provide perhaps the most extensive and well-documented characterizations of asbestos concentrations inbrakeservicingfacilities.providingdataforcarandtruck mechanicsusingavarietyofcleaningtechniquesduringvarious timeperiods.Duringthe1970sandeariyl980s,mostofthesur- veys by NIOSH were conducted in garages that used cleaning methodsconsistentwiththoseusedinpreviousdecades.suchas the use of compressed air to blow off brake parts. 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HWBUI0009528 EXPOSURE OF MECHANICS TO ASBESTOS 793 thebrakedust,suchasericlosedhigh-ef ficiency particulate air (HEPA) vacuum systems. ThefiretNIOSHinvestigationofabrakerepairfacilitywas conducted in 1972;<n> however, the report is unclear as to whetherthesamplescollectedwerepersonalsamples.Also,be cause the sampling durations were not included, it is unknown whethertheresultsarefoipeakodong'termexposures;thus, theywerenotusedinthisanalysis. In 1976and I977.NIOSH researchers sampled 16 mechanics in seven different brake service facilities.*12-*5* Six of the 7 facilitieswerecommercialautoinobilebrakeservicecentersthat performed from 2 to 45 brake jobs per week, at an average of 65 minutes per vehicle (Table I). The seventh facility, a truck ser vice center, performed an average of 3 brakejobs per week, but servicingtookanaverageof6to9h<>urspervehicleJohnsonet aL*12) repoitedTWAconcentrationsfor26automobiIe(TableII) andfivetxck(TableIII)n!echaiiics,'BecausenQneoftheresuits are referred to as 8-hour TWAs, and where given, the sampling durations are aU less than 8 hours, it was assumed thatthe results were for brake job TWAs. The description of brake servicing operations was as follows: "The vehicle is driven into the repair stall or bay for a brake examination. Pending repairs, the wheels are elevated, removed and then inspected. Loose dust is then cleaned from the drums and brake assemblies by vacuuming, wiping, brushing, using compressed air, or a combination of these methods. Parts are then replaced or repaired as needed and the brake system is reassembledandadjusted. " Although not provided in the report, the mean and standard deviationcalculatedhomthedataforthe26automobilebrake job TWAs are 0.095 and 0.053 f/cc, respectively, with a maxi mum of 0.20 f/cc. For the five brake job TWAs for trucks, the mean and standard deviation are 0.59 and 0.64 f/cc, respectively, with a range of0.05 to 1.68 f/cc. TWo commercial automobile brake service facilities were evaluated by NIOSH in 1979.*1?'14* Oneofthesefacilitieswas. previously sampled by NIOSH in 1977, while the second was an active shop that operated 6 days per week and performed from 35to45brakemaintenancepperationsperweek(TableI).These investigatioiisproyidedthreebrakejpbTWAconcentrationestimates,rangirigfromO.OO6to0,O4f/cc(TableD). During 1979 and 1980, NIOSH collected additional sampIesin6brakeservicefacilities,including2commercialbrake semcegarages,3snunicipalautomobilesemcegarages,and 1 fleetservicegarage. *15,z<!> OneofthecommercialfaciIities,a largebfakeservicegarage.waspreviouslysampledbyNIOSHin 1976 and 1977.(,2) Theseevaluatibns.whichinvolvedsampling times of about 2 to 6 hours, provided brake job TWA estimates forl3additionalmechanicsusingsixdifferentcleanmgmethodsforbrakeservicing.includingcompressedair.compressed air and solvents, dry brushing, wet brushing, squirt bottle wash ing, and vacuuming (Thble 11). Although not reported by the authors,themeanandstandarddeviationareO. 15and0.09f/cc, respectively.witharangeofO,01 to0.28f/cc. The final NIOSH investigations were conducted in 1986, 1987, and 1988 and are summarized in Sheehy et al.(l) Thor ough sampling surveys were conducted at five facilities, each usingadifferentmethodforcontroUingexposuretoasbestos duringbrakeiepair. <27~31* The stated purpose of these surveys wastoevaluatedustcontroItechnologies(TableI).Theyevaluated the effectiveness of two commercial enclosure devices with ventilation provided by a HEPA vacuum, a HEPA filterequippedvacuumalone.abnjshwithrecirculatingcleaningsolution, and cleaning solvents in aerosol cans. The investigators alsoevaluatedasmailservicestationgaragewherenodustcontrol measures were used, and brake repair conducted outdoors by a do-it-yourself mechanic who used a spray can of solvent to wet the brake surfaces and water from a garden hose to flush surfaces. These investigations provide 44 additional brake job TWA measurements, 42 .for autos and 2 for light tracks, all of which were collected for the maximum' of either 2 hours or the duration of the brakejob (Table H). Using detection limits in the statisticalanalysisforthosesamplesinwhichasbestoswasnot detected, we calculated a mean and standard deviation for the 42 auto brake job TWAs of 0.005 and 0.002 f/cc, respectively, with a range of <0.004to0.014f/cc. Other U.S. Studies The only published study of mechanics servicing brakes in the United States other than those conducted by NIOSH was that of Moore in 3998.(!6) Asbestossampleswerecollectedin 31 different brake service facilities (Table I). He describes the objective of his study as the collection ofpersonal samples from thebreathingzonesofautomobilemechanicstoestimatstheir exposures while performing actual brake removal and repair work in different facilities with widely diverse work practices. No specificdescriptionsofrhefacilitiesaresupplied.norare TWA data provided for individual mechanics; however, he does indicate that the brake job durations ranged from 10 to 60 min utes, with an average time of 29 minutes. For the 35 samples collected, the mean and median values were <0.03 and <0.02, respectively.withaiangeof <0.01 toO. 15f/cc(Tableff). German Study Rodelsperger et al.(l7) sampled 31 mechanics servicing pas senger car brakes and 36 mechanics servicing track and bus brakes in West Germany (Table I). Personal samples were collectedgenerallyduringthewho]eservice,but,insomecases, samples were limited to specific dust-generating activities. Based on personal samples of 30 minutes or longer, the authors estimatedmeanconcentrationsformechanicsperformingbrake servicesblowingoutdrumswithcompressedair(0.10f/cc),dry brushingdrums(0.09f/cc),andforcombinationsofactivities involving cleaning out brakes (0.04 f/cc). Brake job TWA concentrationdataforindividualmechanicswerenotprovided.The authorsconcludedthatthemeanasbestosconcentrationduring 9 HWBUI0009529 ) 794 D. J. PAUSTENBACH ET AL. brakeserviceoperationswaslessthanO. 1 f/ccforsamplingdurationsgreaterthan30minutes. Swedish Study Platoetal. (18> provideanevaluationbasedontwenty-three 8-hour TWA personal samples at different car and bus repair shops for the period 1976 to 1988 from a Swedish National Board of Occupational Health database (Table I), Although a table of the measurements is not provided in their article, 20 of these 23 TWA concentrations were estimated from one of the figurespresentedintheirpaper.Thesevaluesrangedfirom 0.02 to 0,20 f/cc, with a mean of 0.10 and a standard deviation of 0.07 free. Although the values from Plato et al.(l8) are for a combinationofvehicles,theywereincludedintheanalystsfor automobiles and light trucks, even though some of the higher valuesaremorelikelyforheavytruckandbusbrakerepairwork. Plato et al.(18> also provide independent estimates ofasbestos concentrations, rather than direct measurements, experienced bycardiuck,andbusinechanicsservicingbrake$between 1938 and 1986, based on the sampling data described above and ap plication of factors accounting for the types of vehicles serviced (car, bus, truck), sizes and ventilation ofrepair shop rooms, task activities, frequency of work, and whether work as a vehicle mechanic was performed before or after 1975. Based on their model, the authors estimated an 8-hour TWA for all car mechan ics of 0.09 free during the period from 1938 to 1986. Australian Study Themostrecentinvestigationofasbestosconcentrationsin brake service garages was carried out in Australia in the late 1990s by Yeung et Personal samples were collected on mechanicsinthreegaragesservicingbxakesforpassengerand lightcommercialvehiclesandonegarageservicingbusbrakes (TablesIAandm) .Allfourofthesamplesyieldedresults belowtHedefectionliniitqf0.05f/cc. undertakenduringbrakeservicing.TheestimatedTWAconcentrationswerecalculatedusingthemeasuredmeanandinaximum concentrationsandthemeanduiationsofhumerousoperations (altboughtheduiationdataandcalculalionsarenotprovided in the article). It was assumed that brake maintenance of four wheelswascarriedoutduringtheworkdayandthatotherinfrequent operations, such as the grinding of brake linings, were one hour in duration. Based on these data and assumptions, Kauppinen and Koihonen(34) estimatedthatthemeanasbestos workdayconcentrationformechanicswasunder0.05frccduring therepairofcaibrakesandundeiO. 1 to0.2f/ccduringtherepair oftnickandbusbrakes.BecausetheseTWAconcentrationestimates were not derived from long-term sample measurements, theyarenotincludedinthisanalysisofTWAconcentrationdala. However.theirestimatesoftheworkplaceconcentratioiisdfasbestosduetobrakerepairarevirtuallyidenticaltotheresults reportedintheUnitedStatesandelsewhere. DATA ANALYSIS A total of 162 TWA asbestos concentrations were found in the published literature for individual mechanics servicing auto- mobileandlighttruckbrakesfromthelatel960stothepresenL An additional 19 TWA concentrations were reported for indi vidual mechanics servicing heavy truck and bus brakes during the same time period. Most of the reported TWA asbestos air concentrations represent brake job TWAs, whereas only a few studies (e.g., Plato et al.(18>)reportdatathatrepresent8-hour TWAs. All of the TWA sampling data were compiled from the avail able published studies and entered into a database for analy- sis.Additkmalinformationwasalsosummarizedonfactoisthat mightaffectairbomeasbestosconcentrations.suchastheyear in which samples were collected, the type of cleaning method employedduringbrakeservicing,thetypeoffacility,andthe estimated number of.brakejobs performed weekly in the garage (level of service) (see Tables I and II). ". Other Studies Providing TWA Estimates . ' . TWo otherdocuments provided estimates of8-hourTWAconcentrationsforniechanicsservicingbrakes-.however.theseestimaites are based on data from studies described previously. Nicholsonetal. (32) estimated an 8-hour TWA concentration of 0.1ffccfprmechanicsinmunicipalgaragesand "an upper limit of dig-average exposure" of 0.2 f/cc for commercial garage mechanics. These estimates appear to be. based largely on the NIOSH data reported by Roberts and Zumwalde/15* The Fed eral Register reported a mean 8-hour TWA concentration of 0.03 f/cc for mechanics servicing vehicle brakes from 1979 to 1984 and a mean 8-hour TWA concentration of 0.012 f/cc from 1986 to 1989, presumably based on NIOSH data. Ail additional study, which was conducted in Finland by Kauppinen and Korhonen/341 provided 8-hour TWA concentra tion estimates for various vehicle mechanics based on short-term samples(generallylessthan30minutes)forspeci ficoperations Conversion of Brake job to 8-Hour TWAs Tocharacterizethehistoricaiexposuresofbrakemechanics in the United States so that one can compare the information with occupational exposure limits, such as OSHA permissible exposure limits (PELs) and American Conference of GovemmentalIndustrialHygienists(ACGIH ) threshold limit values (TLVs), it was necessary to convert the brake job TWA values to 8-hour TWA concentrations. This approach is a standard and customary practice in industrial hygiene, and in the hcldoftisk assessment, when attempting to characterize the risk of lifetime exposure to chronic toxicants. The 8-hour TWAs were estimated by assuming that mechan ics were exposed at the brake job TWA levels during the period of the day they serviced brakes and at the background levels of the garages during the rest of their 8-hour days. The fraction of the day during which a mechanic was actually doing brake HWBUI0009530 ) EXPOSURE OF MECHANICS TO ASBESTOS 795 workateachfacilitywasestunatedbyusingthenumberofbiake mechanics at the facility, the number of hours mechanics work per week, the number of brake jobs per week, and the average durationforabrakejobateachfacility. jobs per week x duration Daily Fraction = mechanics x hours per week [11 The brakejob TWAs were then converted to 8-hour TWAs using the fractions of day, brake job TWAs, and mean background concentrations for the facilities. 8-Hour TWA = (Brake job TWA x Daily Fraction) + [Background x (1 -- DailyFraction)][2] Thevaluesusedwereeithertakenduectlyfrointheapplicable reportoiestinMtedbasedonavailableinformation.Theparauneters usedand the results fortheconversions are shown inTablesII andUI. Concentration Distributions and Statistical Comparisons TheTWAconcentraliondatawereanalyzedstatisticallyto characterizeandcompareasbestosexposurelevelsformechanics performing brake services under various exposure condi tions. The data were characterized based on when the sampling wasconducted,whereitwasdone(UnitedStatesandothercountries),thetypesofclean ingmethodsused.andthetypesofveh iclesserviced(carsandlighttrucksorheayytrucksandbuses). Statisticalcomparisonsweremadetddeterminewhetherdifferencesexistedbetweenexposurelevelsasaresultof(I )thetime ofsampling(1970svs.l980s),(2)thelocation(UnitedStates vs.Europe),and(3)themethodsofcleaningbrakes. Statistical comparisons were conducted where possible, given the limitations of the data to, assess how locations and cleaninginetKodsmayhaveaffectedasbestosconcentrations. To eliminate the impact of the amount of brake work done at a site.thecomparisonsweremadeonlyforthosefacilitieswith the same level of service. Low was'assigned to shops with fewer than 10 brake jobs per.week, medium for 11 to 20, and high for more than 20 brake jobs per week. Nonparametrichethods(Kruskal-WailisandWilcoxonranksum tests) were used for comparisons, because the concentra tion data could not satisfy the homogeneity of variance and normalityassumptionsunderlyinganalysisofvariancemethods.Significance was determined after correcting individual test p-valuesforthemultiplecoiriparisonsthatweremade;specifically, individual test p-value was multiplied by the number of tests. Differences among locations were assessed for early U.S. (1970s),lateU.S.(1980s),andSwedishdata,onlybecausethese data sets all have sufficient measurements for individual me chanics to support such an analysis (42, 42, and 20, respec tively).Assessmentofcleaningmethodswasconductedwithin a location and service level to avoid confounding the interpreta tion of cleaning method influencewithotherfactors.Cleaning methods that were very similar, such as compressed air only and compressed air with a dry brush, were combined to cre ate cleaning method categories for evaluating differences. Early U.S. and late U.S. studies both reported multiple concentrations formultiplecleaningmethodcategories.EarlyU.S.cleaning method categories included compressed air with and without dry brush, wet brush, and vacuum-HEPA for low-service-level shops, and compressed air with and without dry. brush, com pressed air-solvent, and diy brush for high-service-level shops. LateU.S.Iow-service-levelshopswereassumedtousethefoIlowing cleaning method categories: aerosol spray, vacuumHEPA, wet brush-recycle, vacuum enclosure, wet brush, wateifiose -squirt bottle, and no cleaning. RESULTS The TWA concentrations measured for automobile and light truck mechanics, and heavy truck and bus mechanics, are de scribed separately. Differences in asbestos concentrations relatedtodifferentbrakecleaningmetiKxisareevaluated.comparisonoftheasbestosconcentrationsexperiencedbyU.S.and European mechanics repairing automobile brakes during the same time period are made, and changes in exposure concentra tions over time from the 1970s to 1990s are evaluated. Automobiles and Light Truck Mechanic Exposures Automobilesahdlighttiuckswereevaluatedtogether.be- cause the tasks involved in servicing the brakes and the durationsofthebrakeservicingweresimilar.Themearisandranges fortheninestudiesthatproyideddataontheaiibomeconcentrations during the actual 'brake job (rather than 8-Tiour TWA samples) are presented in Figure 1. The mean brake job TWA for the 141 automobile mechanics evaluated between 1968 and 1996is0.05f/cc,witharangeofQ,004toD.28f/cc.Itisnotable that brake job TWA concentrations for the more recent surveys in the late 1980s arid 1990s are generally much lowef.than those reported for mechanics working in the 1970s. and early 1980s. These lower concentrations are not surprising, given the greater awareness and concern about exposure to airborne dusts of any type by most workers. Theestimated8-houiTWAconcentrationsfortheabovenine studies, and the measured 8-hour TWA concentrations from Hickish and Knight*9' and Plato et aL*18' for automobile and light thick mechanics, are presented in Figure 2. The mean 8-hour TWA concentration based on 162 values is 0.04 f/cc. The rhaximum reported 8-hourTWA was 0.68 f/cc from Hickish and Knight,*9' withthenexthighestreportedvaluebeing0.20f/cc. The relatively high value from Hickish and Knight is for a me chanic who cleaned the brakes of 11 cars in one shift, which was an unusually high number of vehicles serviced in a day (two to threewasmoretypical). ) HWBUI0009531 796 D. J, PAUSTENBACH ET AL t Maximum 9 Mean X Minimum [Date-of sampling] QSHA 8-hour PEL free (Year) 0.1 (1994) . -r - . tft O 0 3, Note: Dates tefiateMh&ses ampublish dates; ft different than tee publish date. in:s^uam bractote ata sampling FIGURE 1 Brakejobtime-weightedaverage(TWA)asbestosconcentrationsfonnechanicsservicingbrakesonautomobilesandUghttrucks. Heavy Truck and Bus Mechanic Exposures Fewer TWA concentration,measurements are available for mechanics servicing heavy track arid bus brakes than for those servicing automobile arid light thick brakes. The means and ranges for the four studies providing brake job TWAs for heavy tracks and buses are presented.iri Figure 3. Thb mean brake jobTWAconcentrationfoithel8mechariicsevaluatedis0.21f/cc, with a maximum of 1.68 f/cc. The estimated 8-hour TWA concentrations for die above four studies, and the measured 8-hour TWA from Hickish and Knight(,) for heavy track and bus mechanics, are presented b Figure 4. The mean 8-hourTWAconcen{ration, based on 19 data points, is 0.25 f/cc. The maximum reported TWA was 1.75 f/cc from Hickish and Knight,*?5 with the next highest value being 0.87 f/cc. As for the automobile and light truck mechanics, the brake job and 8-hourTWA concentrations for truck and bus mechanics were generally lower in surveys from the late 1980s and 1990s thanfiromsurveysforearlierperiods.AsshowninFigure5.the 8-hourTWAconcentrationsformechanicsservicingheavytrack andbusbrakesaresigni ficantly greater than those for mechanics servicingautotnpbileandlighttruckbrakes.Thisdifferenceis likelyduetoseveralfactors.Thebrakesohtruclcsandbusesare largerandrequifernoretimetoservice.Inaddition.tnickand busmechanicsgenerallyreplacejustthebrakelinings,which oftenrequiresrivetbgandmachining.Becauseautomechsuiics normallyreplacetheentirebrakeshoe --notjustthelining -- thesedust-generatbgoperationsarenotusuallypeifonnedby auto mechanics. Eight-Hour TWA Concentration Distributions It is apparent that the data from the NIOSH surveys provide the most complete characterization for estimating the 8-hour TWA concentrations experienced by brake mechanics i ntheUnitedStatesinthe1970sandlate1980s.Thecumulativc distribution plots of the NIOJJH survey data (Figure 5) show that 8-hour TWA concentrations for automobile mechanics in the 1970s were generally within a narrow range, with a 50th percentilevalueof0.07f/ccanda90thpercentileof0.10f/cc. HWBUI0009532 im m; o 10' yjO ceann< <E1> 11 q.t i f-*o ; ccz 3Q0O 5& 0.011 * 0:0011 EXPOSURE OF MECHANICS TO ASBESTOS 12(1071) "I2;(ie76) j Maximum p Mean JL Minimum 797 Pate of sampling} OSHAff-hpur PELMm (Year) teoo ISfSfeT oxk o> ffl OsO @ oo ,t~ _i-.it Q a < 8 CD -w S> fi S. M f 1 a? oc <a3 s 0> O) fstote:- Dates' in p&terifttesSs,afe.pu!jli6h daifesrdates in square bracfets ar sampling dates, if differenlte'anihepublisli'dare, FIGURE 2 Eight-hourtune-weightedaverage(TWA)asbestosconcentrationsforinechanicsservicingbrakesonautomobilesand light trucks. (That is, it can be expected that at least 90% of the mechan ics were exposed to concentrations below 0.1 f/cc during that 2(byearperio4)ThecumulativedistribuUonplotfortheIatef NIOSH. survey in the 1980s shows a substantially lower and nariower^homTWAconcentrationdistribution.withboththe 50thahd90thpercentilesat0.002f/cc.Theplotforheavytruck andbusbrakemechanicsindicatesthattheSOthpercentilevalue for this group (0.08 f/cc) was similar to that for automobile brake mechanics from the 1970s NIOSH studies but that the 90thpercentilevaluesfortruckandbusmechanics(1.65f/cc) wassubstantiallyhigherthanthatforautomobilemechanics. centrations, respectively). . The distributions for the three data sets are shown in Figure 5. A statistical comparison of 8-hour TWA concentrations derived from the NIOSH studies ofUnited States mechanics from 1976 to 1982 and the 8-hour TWAs re ported for Swedish mechanics fribm 1976 to 1988 found ho significantdifferehceinmeancoricehtrations(seeTabieiy).U.S. mechanics evaluated in the late 1980s by NIOSH were exposed tosigni ficantlylowerairbomeconcentrationsofasbestosthan eithertheearlyU.S.orSwedishinechanics.Thisdifferenceis iikelyduetotheimprovedcleaningmethodsdiscussedbelow. Comparison of U.S. and European Brake Mechanic Exposures Differencesamonglocationswereassessedusingtheearly U.S.(1970s),IateU.S.(1980s),andSwedishdatascts,because they were the only ones that had sufficientnumbersofindividual samples for statistical analysis (42, 42, and 20 TWA con TWA Concentrations Relative to Cleaning Method Asearlyasl970,studiesorsurveysoftheconcentrationof airborne asbestos for vehicle mechanics servicing brakes noted that the cleaning process, particularly compressed air blow-out ofdnirnbrakes.wasthemajorcontributortoairbome fiberlevels. The mean and ranges for brake job TWAs using the various cleaningmethodsarepresentedihFigure6.Thcdistributionsof HWBUI0009533 798 D. J. PAUSTENBACH BT AL. (0 I ugjoz << SE1T pz& <Dq Oz 1" 1.8 1.6 14 1.2 id QM P .04 0=18 n=5 T Maximum 9 Mean X Minimum 05 P m .'0.0 n-io |jh3a> ?a-g. P>CSQft. gjOl ^ I. O3: CP k * c-2^. r. 8 sz za>- o *" jg "3 1*} ' CC n-2 -JO*-- O 3- CD -oc> coq> jB *s-' m n6-1 8 fflC > r FIGURE 3 Brakejobtime-weightedaverage(TWA)asbestosconcentxationsformechanicsservicingbtakesonheavytrucksandbuses. to fez |g || Sg dcz 38 1.8 ' n = 19 1.6 - 1.4 1.2 - 14 - 0.8 - 0.6 - 0.4 * 0.2 * 0.0 J 1III . "? 8 t O ft -- 1 -SLp gvf CO *E o> o> "0c jr eft Lse o X n=5 < >. Sgf T 0 eh gg H. " 0=i 10 (avg-) O h- ^ Q> CP S-^r <d -S-s CC T Maximum 9 Mean X Minimum 0=2 ---- w<3i tt m 0r-3. i CD f8 (O' n-1 Q 1I ~c8 CD .CD FIGURE 4 Eight-hourbrakejobdme-weightedaverageCTWAJasbestosconcentrationsfonnechanicsservicmgbrakesonheavytnicks and buses. HWBUI0009534 EXPOSURE OF MECHANICS TO ASBESTOS 799 FIGURE 5 Cumulativedistributionsof8-hourtime-weightedaverage(TWA)asbestosconcentrationsforniechanicsservicingbrakeson automobiles, trucks, and buses. the most frequently used methods are shown on Figure 7. With the exception ofa few TWA concentrations, most of the data are from NIOSH studies. Itisevidehtfromtheplotsandthestatisticaltestresults summarized in Table IV that the'introduction of dust control technologies significantlyieducedboththemagnitudeandvari abilityofasbetosexposuresforbrakemechajriicsAsshownin Figure7,the5()thand9bthpercentiiebrakiejobTWAconcentia- tionsfonnechanicsusingcompressedairforcleaningduringthe 1970s and early 1980s were approximately 0.10 and 0.18 f/cc, respectively. The use ofsolvents with compressed air in the early 1980s reduced the 50th and 90th percentiles to about 0.03 and 0.08f/cc,respectively.Theusep{wetbrush/recycle,HEPAyacuum. and vacuum enclosure reduced moslasbestosexposures tolessthanO.Olf/cc --levelsatorbelowthedetectionlimitfor NIOSH sampling. The use of these dust control technologies served several purposes.Theydramaticallyreducedthepeakexposuresduring cleaning, they prevented the distribution of airborne dust into other areas of the work environment, and they kept brake dust from being deposited on the floor of the work area, where it couldsubsequentlyberesuspendedbyfoottraf fic or sweeping. The 50th and 90th percentile brake job TWA concentrations formechanicsusirigcompressedairforcleaningaresiinilarto thosefpiU.S.mechanicsasagroupinthel970s,likelybecause compressed air was the method most frequently iised for brake cleaning during that period Changes in Exposures Overtime . .. The decrease in 8-hour and brake job TWA asbestos concen- trationsinthelatel980sisevidencedbythedistribudonsof early and late NIOSH values for auto brake mechanics shown in Figure5.ThisstatisticalcoihparisbnissurmnarizedinTablerV. BasedontheayaJlabledata,itisclearthatmuchofthedecrease is due to dust control measures^ that were'first introduced in the latel970s.However;tlieiritrbductioriofdiscbrakesduringthis period would also have led to decreased exposures for mechanics.Duringtheperiodofnearlyallthesestudies.discbrakes were placed predominantly only on the front wheels because of problems in using disc brakes in conjunction with the rear parking brake system. Because disc brakes have many fewer places where dust can collect than do drum brakes, there would havebeenmucblessbrakedustavailableforsuspensionintothe HWBUI0009535 800 D. J. PAUSTENBACH et al. ResuItsofstatisticalcomparisonsoftime-weightedaverages(TWAs)bytimeandlocationandcfeaningmethodandlevel of service Type Cleaning method Service Number of Standard level results Mean deviation Test conclusions Time and location (8-hour TWAs) EarlyUnitedStates A NA LateUnitedStates B NA NA NA Swedenc NA NA Cleaning methods and level of service (brake job TWAs) EarlyUnitedStates A Com air w/ & w/o dry Low brush Wet brush Vacuum & HEPA EarlyUnitedStates A Compresed air w/ & w/o Dry brush High Compressed air w/solvent Dry brush LateUnitedStates B Aerosol spray Low Vacuum & HEPA Wet brush/rec Vacuum enclosure No cleaning Wet brush Water hose & squirt bottle 42 0.063 0.032 42 0.0021 0.00036 Significantly different from early U.S.,Sweden(w/multipietest correction) 20 0.10 0.067 4 0.028 0.0050 Significantlydifferentfromwet brush(w/omultipletest correction) 3 0.25 0.026 Significantly different from com air w/ & w/o dry brush (w/o multiple test correction) 1 0.010 22 0.10 0.053 Significantly different from com airw/solvent,drybrush(w/o multiple test correction) 4 0.049 0.033 Significantly different from com air w/ & w/o dry brush (w/o multiple test correction) 2 0.20 0.0071 Significantly different from com air w/ & w/o dry brush (w/o multiple test correction) 3 0.0080 0.0053 Significantlydifferentfromwet brush/rec,vacencl(w/o multiple test correction) 7 0.0069 0.0035 Significantlydifferentfromwet brush/rec,vacencl(w/o multipie test collection) 10 0.0041 0.000316 Significantly different from aerosol spray, vac & HEPA- . (w/o multiple test correction) 8 0.0040 0 Significantly different from aerosol spray, vac & HEPA , (w/o multiple test correction)- 1 0.0080 -- 1 0.0040 1 0.0070 -- Note: Sigjuficantdifferencesdeternunedbyoveralltype-lerrorrateQfO.OS. AEarly United States are samples from the 1970s by NIOSH. BLate United States are samples from 1980s by NIOSH. .. cSweden are samples from 1980s by Plato et al. air during brake servicing operations. In addition, non-asbestos brakepadmaterialsbegantobeusedindiscbrakesinthel980s. Although there are no published data on the exposure of ve hicle mechanics to asbestos during brake repair activities prior to 1968, it is possible to speculate on earlier exposure lev els for automobile brake mechanics. With the introduction of bonded brakes in 1948, the need for drilling, facing, and grinding was significantly reduced, and with factory-supplied, tapered, bondedbrakereplacementsavailableinthel950s,theneedfor beveling was also greatly reduced.1'* By the early 1960s, the HWBUI0009536 EXPOSURE OF MECHANICS TO ASBESTOS 801 using different cleaning methods. methods for performing brake jobs on autos were similar to those used in the 1970s--cleaning brake assemblies with compressedakorawirebnishandieplacingdieentirebrakeshoes withfactorysuppKed,tapered,bondedshoes.Thus,itisquite likely that the exposure levels experienced in the late 1950s and the 1960s were similar to those in the 1970s. DISCUSSION .ThisevaluationofTWAairbornecpncentrationsofasbestos due to brake dust experienced by mechanics presents a compre hensive picture of exposure. levels for brake repair work over thepast30years.Themeanconcentrationidenti fied (e.g., about 0.04f/cc)appearstobeconsistentwiththosereportedinother evaluationsqfmechanicexposuresandaresubstantiallylower thanlevelsreportedforworkersinotheroccupationshandling asbestos-containing products. SimilarHiestoOtherStudies Thisanalysisfoundthatthe8-hourTWAconcentrationsfor brake mechanics obtained or derived from the early NIOSH sur vey data<!5* weresimilartothoseestimatedbyPlatoetal. (|8) for Swedish automobile mechanics in the 1970s (the mean for both was about 0.04 to 0.09 f/cc). Likewise, data from the United States (e.g., NIOSH) were similar to those estimated for Finnish mechanics by Kauppinen and Korhonen*34* using short-term concentrationdata(meanofabout0.05f/cc).Theconsistency among these independent 8-hour TWA airborne concentrations for asbestos due to brake dust indicates substantial similarities in brake repair operations and the asbestos content in brake linings in various countries during the 1970s and 1980s. The simiiariiyinresultsbysoinanydifferentresearcheis.insuch different geographic locations, gives significant confidence in the conclusions. Comparison to Regulatory Standards TheU.S.regulatoiystandardforoccupationalexposureto asbestos has changed numerous times over the last 30 years.135* In 1971, OSHA set a PEL for asbestos in workplace air of 12 f/cc as an 8-hour TWA, which was based on the TLV established by ACGIH in 1968. Since then, the PEL has become more.strict over time. Specifically, in December 1971, OSHA issued an emergency temporary standard that lowered the asbestos PEL to 5 f/cc, and in June 1972, OSHA officially lowered the PEL standard to 5 f/cc for 1972 and 2 f/cc commencing in July 1976. In 1986, the PEL was lowered to 0.2 f/cc. and in 1994, it was again lowered to its present value of 0.1 f/cc. Comparisons of themeasuredasbestosairbomeconcentrationsingaragestothe OSHA PEL at the corresponding times indicate that both the HWBUI0009537 802 D. i. PAUSTENBACH ET AL. BRAKE-JOB TWAASBESTOS CONCENTRATION (me) Note: Graph presents data from studies tor which there are measurements reported for individual mechanics ancf a reported cleaning method Cleaning methods with fewer than five data points are not shown. FIGURE 7 Cumu(ativedistributionsofbrakejoblime-weightedaverage(TWA)asbestosconcen!rationsformechanicsscrvicingbrakeson automobilesandlighttrucksusingdifFerentcleaningmethods. brakejob and 8-hour TWA concentrations of asbestos for brake to 100 times less than for those persons who manufactured the mechanicswereconsistentlybelowtheapplicablefederalstan- brake linings. dard. This observation is further confirmed by the lack ofOSHA citations of garages for exceeding the PEL for asbestos from 1972-2002. Characterizing; Variability . As with-'any'"analysis of multiple studies, 'there; were saute Unutationsintlieavailabledataforestiinatiiigtherin'eaii8-libur: Comparison to Other Occupational Exposures TWA concentrations to which brake mechanics were.exposed:: To better understand the relative magnitude of brake me- over time. Forexaitiple, nearly all of the':samplirig;claia cpUectkl' chanicexposures.onecanevaluateotheroccupationsthathan- in the field on brake mechanics involved ;!- to 2-hour samples; dledrawasbestosanduseditinthemanufactureofothergoods. thus, the data needed to be corrected to predict the typical 8-hour From 1964 to 1985, for example, the ILS. Public Health Ser TWA airborne concentration to which mechanics were exposed. vice and NIOSH conducted seven studies at brake manufactur Few 8-hour TWA samples were collected on brake mechanics, ing facilities.43*-41* During the 1960s, the mean asbestos con- becausethemdustrialhygienistsapparentlycondudedtftatif centrafionfor381 samplescolleetedduringthreestudieswas . the results of a shorter sampling period (e.g., during a brakejob). 6.0 f/cc, with a range of 0 to 130 f/cc. In the 1970s, the mean did not exceed the'PEL, then sureiy; the 8-hourTWA woiitd 'be value for 269 samples from two facilities was 1.5 f/cc, with a less than the PEL, given that the remainder of a mechanic^ day range of 0 to 17.5 f/cc. In the 1980s, the mean value for 49 wouldhavebeenspentawayfrombrakerepairactivities.Also, samples from two facilities was 0.38 f/cc, with a range of 0.01 because exposures were sporadic and of short duration, they to 1.1 f/cc. By comparison, the mean brake job TWA for au couldbeestimatedbyconductingatime/motionanalysis.which tomobile brake mechanics was 0.11 f/cc during the 1970s and accountedfortheactualtimeduringwhichexposuresoccuned. 0.005 f/cc during the 1980s. Thus, at comparable times, auto This analysis was limited by the lack ofcertain information in mobile brake mechanics had asbestos exposures that were 10 thereportsregardingthevarioustasksperfonnedbymechanics HWBUI0009538 EXPOSURE OF MECHANICS TO ASBESTOS 803 duringthesamplingperiod(asweUastheentireworkday).Except for several of the NIOSH surveys, little information was provided on the number of brake jobs performed per day by mechanics, or the amount of time spent each day actually per forming brake repair woric. None of the long-term studies pro vided specificmechanictime/motiondataforactivities.which would have enabled better comparisons of the data. Several of the original authors ofthese studies were contacted in an attempt togainabetterunderstandingofwhatwasactnallydoneandfor how long. They provided an adequate verbal account of what they did, but either the original notes describing their work had been discarded, or much of the desired information was never recorded. Though there are some limitations associated with these data, comparedtothemajorityofoccupationsthatweresurveyedfor asbestosconcentrationspiioito1980,theaccumulateddataare quite good. For example, almost 200 measurements were iden tified and included in this analysis. The data were sufficient to compare the ranges of exposure for brake mechanics working on different types of vehicles, in different countries, during differenttimepeiiods,andusingdifferentcleanmgmethods.The brake job TWA data set establishes the upper bounds of the asbestosconcentrationstowhichmechanicscouldbechroideally exposed if they performed brake jobs 40 hours per week for many years. Because the process of changing drum brakes and theasbestoscontentoftheliningsdidnotchangeappreciably ffomaboutl940tol975,thesedatashouldbeapplicableforthe entire 35 years during which drums were the primary braking mechanism used on automobiles in the U.S. Airborne concen trations of asbestos for auto mechanics would have decreased substantially only over the past 20 years due to the fewer as bestos brake linings on cars (conversion to nonasbestos linings), the conversion to disc brakes, and better techniques for controllingexposuretobrakedustinrepairshops. CONCLUSIONS Based on this review and. analysis of the available data on thecpncentrationsofairbomeasbestosforvehiclemechanics servicing brakes, several conclusions were reached: TWAconcentrationdatafrorrithelOpublishedstudies are sufficient tocharacterize exposures ofvehicle brake mechanics from the 1970s to the present with a high degree of confidence. The 8-hour TWA concentrations for auto brake me: chanics in other industrialized countries studied were similarduringthesametimeperiodsfortheyears 1970 to 1990. As dust control methods were implemented, the 8-hour TWA concentrations dropped by at least an order of magnitude from 1970 to 1990. Airborne concentrations ofasbestos during the process of changing brake linings (1- to 2-hour samples), as well as the 8-hour TWA concentrations, were consis tently below the applicable OSHA occupational stan dard for the 1970s, 1980s, and 1990s. Becauseboththecleaningandbrakereplacementmethods weresimilarafter the introduction oftapered bonded brakes, it is quite likely that asbestos exposure levels inthelatel950sandthel960sweresbnilartothosein the 1970s for auto brake mechanics. For comparable time periods, asbestos TWA concen trations for vehicle brake mechanics were 10 to 100 timeslowerthanthoseexperiencedbyfirictionproduct manufacturingworkers. 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