Document 3QX1Gde6wQ5G4xqgzjp6b893a

FILE NAME Brakes BRK DATE 1976 DOC BRK062 DOCUMENT DESCRIPTION Journal Article - Asbestos Exposure During Brake Lining Maintenance and Repair ENVIRONMENTAL RESEARCH 12 110-128 1976 Copyright '1976 Reprinted from Environmental Research 12 110 Academic Press Inc. 1218976 Printed in U.S.A. Asbestos Exposure during Brake Lining Maintenance and Repair,, ARTHUR ROHL ARTHUR M. LANGER MARY S. WOLFF AND IRVING WEISMAN Environmental Sciences Laboratory Mount Sinai School of Medicine of the City University of New York New York New York 10029 Received December 10 1975 Data obtained on asbestos exposure of garage mechanics during brake lining maintenance and repair work show that fiber concentrations frequently in excess of regulated limits are common The presence of chrysotile ranging from 2 to % in brake drum dusts was demonstrated by ray diffraction transmission electron microscopy selected area electron diffraction and electron microprobe analyses Unaltered chrysotile was found both in fiber and fibril form in air and brake drum dust samples The chrysotile asbestos content of personal air samples taken during automobile brake repair work was measured both by optical and electron microscopic techniques While a positive correlation exists between the types of measurements the present technique of optically counting asbestos fibers may considerably underestimate the levels of total asbestos exposure INTRODUCTION During the past decade significant disease risk has been found associated with the inhalation of asbestos fibers in a number of occupational and environmental circumstances other than in asbestos mining milling and manufacturing where serious hazard was already known Wagner et al 1960 Newhouse and Thompson 1965 Selikoff et al 1964 1965 Harries 1968 Such exposures were found in the construction industry and in shipbuilding as well as in other industrial settings where asbestos products were used More recently asbestos exposure has been suggested to occur during automotive brake lining repair and installation work and measurable concentrations of asbestos fiber were observed in the work environment of workmen involved in these opera- tions Hickish and Knight 1970 Hatch 1970 Boillat and Lob 1973 With limited data available however uncertainty remained regarding the type and extent of asbestos exposure during this work Some investigators have questioned whether free asbestos fibers survive the high temperatures produced during braking action Lynch 1968 Hickish and Knight 1970 Hatch 1970 contending that asbestos decomposes as a result of the high point contact temperatures produced at the interface of the brake drum or disc and brake lining We have sought to obtain information concerning asbestos exposure of workmen engaged in brake lining maintenance and brake shoe installation by analysis of residual dusts recovered from brake linings and by direct measurement of the * This research was supported by Center Grant ES 00928 of the National Institute of Environmental Health Sciences of the U.S. Department of Health Education and Welfare Assistance was also provided in part by the Health Research Council of the City of New York HRC U 2329 and by the Ford Motor Company Copyright '1976 by Academic Press Inc. All rights of reproduction in any form reserved 110 ASBESTOS EXPOSURE 111 free asbestos fiber content of workroom air in areas where these operations take In the United States an estimated work force of at least 900,000 auto pmleaccheanics and garage workers is potentially exposed to asbestos in the servicing of both brake and clutch linings Furthermore much brake dust enters the general environment during automobile use Jacko and DuCharme 1973 to add more to the burden of asbestos air pollution Selikoff Nicholson and Langer 1972 Asbestos in Friction Materials In the United States an estimated 118 million pounds of asbestos is used annu- of brake friction materials Jacko and DuCharme 1973 ally for the production the asbestos in the material sold is After processing cutting grinding punching contained in approximately 103 million pounds per year In addition asbestos automotive clutch friction materials amounts to 4.5 million pounds annually Major Constituents of Brake Linings A number of materials is commonly used in the manufacture of the three major automotive brake lining components binder fiber reinforcer and property mod- ifier These are listed in Table 1 Binder The binders used in the automotive industry today are primarily resins which are noted for high binding efficiency and ability to phenolic materials have been used in varying pro- withstand pyrolytic breakdown Other portions and in addition to resins for binder improvement Table ) TABLE 1 COMMON COMPONENTS OF AUTOMOTIVE BRAKE LININGS Binder and organic friction modifiers Phenolic resin Rubber Tire scrap Pitch Cork Gilsonite Cashew nutshell resin and particles Drying oils Fiber reinforcer Chrysotile asbestos grades 4-7 Unaltered Calcined Mixed fiber Property modifier Lead compounds Zinc compounds Antimony oxide Iron oxide Copper metal Brass chips Clay minerals Barite BaSO4 Wollastonite CaSiO Quartz SiO2 Cryolite NaAIF Rottenstone SiO2 Coke C Coal C Gilsonite C Graphite C Carbon black C Molybdenum sulfide MoS2 Fluorspar CaF2 * See Carroll 1962 Anderson 1969 Anderson 1973 Jacko and DuCharme 1973 Bark et al 1975 b Chrysotile fiber constitutes about 50 by weight of most automotive brakes currently manufactured in the United States 112 ROHL ET AL Fiber For fiber reinforcement of the friction product chrysotile asbestos is used almost exclusively The mineral typically comprises from 40 to % of the brake product Fiber grades 4 through 7 are used and occasionally several sizes are admixed or even calcined to improve performance characteristics Modifiers Perhaps the widest range of materials used in friction products are the property modifiers Nineteen representative compounds are listed in Table 1 Modifiers are used for a number of purposes they are included to increase brake shoe density making the brake surface able to withstand high pressures e.g. barite they are included as lubricants to reduce the coefficient of friction along the brake surface and thereby prevent grabbing e.g. lead compounds they act as friction agents increasing the coefficient of friction and enhancing the braking action of the shoe e.g. brass chips they act as internal abrasives which help to recondition the braking surface and remove deposited decomposition products e.g. rottenstone quartz they act as heat sinks reducing binder pyrolysis and fiber decomposition thereby extending the useful life of the lining e.g. brass chips metals etc. It is important to note that one major purpose of the reconditioning agents is to retard the formation of forsterite a mineral not originally present in the brake material but created by dehydroxylation and recrystallization of chrysotile asbestos at high temperatures which may accumulate on the surface of the brake lining The hardness of the forsterite hardness 6.5-7.0 is such that it tends to score and gouge brake drums and discs hardness 3-3.5 degrading them prematurely Therefore recrystallization of chrysotile to forsterite is an unwanted effect hindered insofar as possible by the modifiers present in the matrix Materials of Biological Interest Asbestos quartz and heavy metals are constituents of automotive brake lin- ings each warranting special consideration from the viewpoint of biological activity The focus of this report is limited to the problem of chrysotile asbestos exposure Mechanisms of Degradation of Brake Linings during Use Brake wear is dependent upon many factors such as the temperature generated at the surface of the brake shoe during braking operations At any one time only a small percentage of the rubbing area is in contact with the wheel with hot spots generated ranging up to 800 to 1000 Carroll 1962 Anderson 1969 It is not uncommon during moderate braking action to attain temperatures as high as 500 Carroll 1962 Some investigators have suggested that in addition to binder pyrolysis chrysotile completely dehydroxylates under these conditions and reduces to powder where it is swept off the brake facing Carroll 1962 How- ever this hypothesis is oversimplified in that other important processes besides thermal wear contribute to shoe breakdown and brake shoe degradation Burwell 1957 For example the effects of abrasive wear and macroshear have been investigated When monitored by ray diffraction chrysotile in brake materials displays structural strain and substructure fragmentation caused by shear during braking processes Mizutani et al 1973 This shear strain produces material fatigue which with binder pyrolysis can cause brake lining disintegration at ASBESTOS EXPOSURE 113 below those required for chrysotile dehydroxylation Therefore temperatures far altered or unaltered chrysotile brake lining disintegration may liberate partially fibers Thermal DecompositionanoaflyCshirsysiontdiilceates that chrysotile undergoes dehydroxylaforsterite Differential thermal anhydrous magnesium silicate to tion at 650 to 680 and recrystallizes 1966 Daykin 1971 Berry 1971 Mg2SiO4 at about 810 to 820 e.g. Martinez are subject to great Monkman 1971 Harrisof 1th9e71cheTmhiessteryteomfptehreatfuirbeerrapnagrteiscle size instrumental variation as a function etc. Also forsterite has been noted to form during variations sample packing lower temperatures Bates and Comer static heating at considerably and Dresher 1966 p1r9o5l7onMgaerdtinez 1966 Brindley and Hayami 1965 Naumann and in excess of 570 are required for dehydroxylation In general temperatures Extensive study of both the thermal incipient forsterite formation in chrysotile and design indicates that behavior of chrysotile and brake lining composition chrysotile fiber may survive in the decomposed lining dust METHODS Analysis of Brake Drum Dust DecomdprousmeddusLtisniwnegre collected and examined by Ten samples of automobiledibfrfarkaection transmission electron microscopy and optical microscopy ray with microchemical capability for the purpose of scanning electron microscopy determining the presence or absence of chrysoltiiglhet.was generally not useful for Optical microscopy employing polarized considered re- in brake drum dust A number of factors are detecting asbestos including the low relief and birefringence of sponsible for this phenomenon matrix consisting largely of road dust resin chrysotile and the nature of the microscopic preparations readily binder and pyrolyzed residue which in optical obscures the smaller asbiensttohse fciobnetrisnuous and step mode was performed on in all ten ray diffractometrryeflections hkl = 002 020 004 were observed all dusts Chrysotile determination of chrysotile content was made by compari- samples Quantitative dilution standards The weight son of unknroawnngsedwfirthomcaalbioburtat2io-ns1o5f cwhirtyhsoatnilaeverage ranging from 3-6 Lead occurrence calcite mica clays barite graphite and alpha particles compounds quartz In several samples weak diffuse reflections suggested the were identified as well could not be made using this of forsterite but positive identification presence technique Identification of Chrysotile by Electron Microscopy and elec- Transmission electron microscopy selected area electron diffraction of the United Automobile Workers Local Union No. 259 and the * We acknowledge the cooperation obtain these samples in auto Automobile Dealers Industrial Relations Association in helping us under at maintenance shops in the New York area Each sample was taken from a typical job way the time 114 ROHL ET AL tron microprobe analysis of the brake dusts were carried out on each of the ten samples after preparation by a technique which disperses the dust particles in a nitrocellulose film without altering particle size distribution Free chrysotile fiber bundles and fibrils were observed in all ten samples Fig ) Selected area electron diffraction analysis of representative fibers demonstrated the preservation of the chrysotile structure Figs 2A B Some patterns displayed arcuate reflections suggestive of interfibril rotation and intrafibril displacement Figs 2A B Occasionally fibers were observed without characteristic chrysotile morphology with mottled surfaces and obliterated fibrils indicating partial or complete recrystalli- zation Electron diffraction patterns obtained from these particles displayed = a Wns ee) FIG 1. Electronphotomicrograph of large chrysotile bundle in brake drum dust 38,000 ^ magnification Other particles include phenol resin binder and road dust debris ASBESTOS EXPOSURE 115 FIG 2. Selected area electron diffraction patterns obtained on fibers of chrysotile obtained during air sampling at brake repair shops In A the reciprocal a axis is marked a as are the layer lines in the Okl series Indexing of upper right quadrant yielded 16 reflections corresponding to single crystal ray diffraction analysis of Whittaker and Zussman 1956. Pattern in B displays smearing of reflections in a clockwise manner suggesting interplanar rotation polycrystalline characteristics of multiple random reflections or Scherrer rings rather than the distinctive single fiber chrysotile pattern Fig 2B Microchemical analysis with a probe technique on the unaltered fibers showed them to possess the usual Mg ratio of chrysotile In addition to free chrysotile fiber bundles and fibrils chrysotile was also frequently observed projecting from the margins of binder fragments Fig 3 Free asbestos fibers present in the decomposed lining dusts were sized at 42,000x magnification The results seen in Table 2 show that most fibers are too small to be seen by optical microscopy almost all of them are shorter than 0.4 ...m in length virtually all are of respirable size -5 ...mHatch 1970 in reporting on optical fiber counts obtained from brake cleaning operations with compressed air jet found that 94 of the fibers fell in the 2-5 ...mlength category while only % were longer than 5 ...mJacko and DuCharme 1973 made size distribution measurements of asbestos fibers in brake dusts generated during dynomometer tests using both optical and electron microscopy They found at magnifications of 22,000 that 30 of the fibers were from 0.25 to 0.50 ...min length and that 60 were longer than 0.5 ...mSome discrepancies between our data and those of Jacko and DuCharme may be attributed to their use of the lower magnification 22,000 vs 42,000 at which fibers shorter than 0.20 mmay not be easily seen or identified on the electron microscopic screen Thus both the optical fiber count data in other studies and the electron microscopic fiber size distribution data 116 ROHL ET AL Fig 3. Electron photomicrographs of brake drum dusts Chrysotile is present in both free fiber and fibril form Opaque granular material is road dust or phenolic binder a ^ 10,800 b x9300 c 30,000 d x30,000 indicate that the chrysotile fiber population generated by brake wear is a strongly skewed one with almost all fibers concentrated in the smaller than 5 ...mregion No attempt was made to size the asbestos particulates Personal Air Sampling during Brake Repair Work Personal air sampling for asbestos exposure during brake lining maintenance and repair was carried out at franchised auto dealer garages taxi fleet repair shops and a municipal truck repair shop all located in New York City.Personal AsistanceAssistancein providing opportunity for sampling was given by the Department of Air Resources New York City ASBESTOS EXPOSURE TABLE 2 LENGTH DISTribution of Chrysotile Fibers in Brake Drum DuST Sample 1 2 3 4 5 6 7 8 9 10 750-1500^ % 40 32 20 26 57 23 50 29 6 11 1500-2250^ % 34 23 25 37 17 9 26 30 41 6 2250-3000^ % 11 32 25 26 4 12 21 21 18 31 3000-3750^ % 11 - 7 12 2 17 10 31 a Fibers counted and sized at 42,000 all fibers have diameters from 250 to 500^ 117 Total % 96 87 70 96 78 56 99 97 75 79 air samples were taken during and after brake repair work and at varying distances from the work sites in other areas of the garages and shops The latter samples were intended to provide information concerning levels of asbestos exposure which garage employees other than those doing brake work might experience Asbestos Exposure during Automobile Brake Repair Work Air samples were first taken in the breathing zone of mechanics doing brake measurements were taken over periods of 3-8 repair work These peak exposure dust from brake drums The air minutes during which the workers were blowing taken on membrane filters were processed and fiber counts made in samples adopted by the Occupational accordance with the procedures which have been Safety and Health Administration OSHA of the U.S. Department of Labor Bayer Brown and Zumwalde 1975 Essentially the analysis consists of count- ing fibers 5 to 100 ...min a fixed area of a Porton graticule using phase contrast microscopy at a magnification of 400 This microscopic method enhances image contrast and allows large asbestos fibers to be readily seen and counted a When vehicle is brought into a repair shop for brake lining inspection or the wheel is removed and loose dust is removed from the drums and rbeapclkapcleamteenstgenerally by means of a compressed air jet A recent survey of brake repair establishments in Baltimore and Washington revealed that this is the stand- ard method in those cities Castleman et al 1975 A similar situation exists in New York City The cloud of dust that is produced is visible for several minutes afterwards Fig 4 Table 3 shows that fiber concentrations are high in the operator's area under these conditions an average concentration of 16 fibers and that there are significant concentrations at least 20 ft away Background or area sampling during the same operation shows that at least 14 minutes after jet air blowing and up to 75 ft away asbestos concentrations are still measurable even by optical microscopy The data in Table 3 indicate that an asbestos concentration gradient dependent on distance and time is associated with this operation It is evident that any person 65-75 ft away can be exposed Current interim regula- tions of OSHA prohibit concentrations of 5 fibers or more longer than 5 mas 118 ROHL ET AL FIG 4. Removal of dust from brake drum and back garage plate by pneumatic air blowing at automobile a weighted average for workers and illegal after 1976. Regulations set concentrations above 2 fibers will be fibers of air Newly a peak concentration maximum excursion of 10 proposed standards are designed to set a limit of 0.5 fiIbt ers 500,000 fibers with a maximum excursion of 5 was generally found that there fibers most garages Workmen do was minimal if any effort to control dust in not use respiratory protection There was little ness of the potential hazard of brake dust aware- Personal air sampling was also Sanitation truck repair shop conducted where at the New York Department of work are performed Used truck various brake kinds of brake application and repair to remove grease and linings are salvaged by grinding the surface dirt and new linings are ground to expedite break The | ae cement seranereap Ir ASBESTOS EXPOSURE 119 TABLE 3 ASBESTOS Concentrations during AUTOMOBILe Brake SeRVICE *** Operation Blowing dust out of brake drums with compressed air jet Background samples taken at varying distance and lapsed times after brake drum blowing Distance ft 3-5 5-10 10-20 Number of samples 4 3 2 Distance from operation ft 282837 282837 282837 282837 282837 75 Time lapse min oonst oonst oonst oonst oonst 14 Fiber concentration fibers Mean Range 16.0 3.3 2.6 6.6-29.8 2.0-4.2 0.4-4.8 Concentration fibers 0.3 0.8 0.2 0.1 0.1 0.1 Distance Number of Fiber concentration fibers ft samples Mean Range Cleaning brake drums with dry brush Background samples taken 3 minutes after cleaning brake drums with dry brush 1-3 12 2 2.5 1.3-3.6 3 0.1 0-0.2 5-100 Fibers 5-100 min length counted by optical microscopy * The new proposed Asbestos Standard of the U. S. Department of Labor records asbestos exposure in fibers noting that a workman might respire approximately 8 mof air per working day retain- ing an unstudied proportion of inhaled fibers The above table omits reference to air content of fibers < 5 ...min length is then riveted onto a steel plate Some of these operations are similar to those done during the manufacture of brake shoes Table 4 summarizes the results of personal air sampling in the course of this work During light grinding of truck brake shoes Fig 6 an average peak concentration of about 4 fibers was found in the breathing zone of the operator The data show that measurable fiber con- centrations are found 25 ft or more away At a distance of 25 ft for example a concentration of 1 fiber 1,000,000 fibers was found Much larger numbers of shorter fibers would simultaneously be inhaled During the beveling of truck brake shoes on a grinding machine very high concentrations of fibers were found in the vicinity of the operator The average of five air samples was about 37 fibers Area samples taken up to 30 ft away from this operation demonstrated the presence of airborne fibers It was of interest to note that at the time of this sampling from eight to 15 other garage mechanics were working within this 120 ROHL AL ey } eo FIG 5. Beveling of truck brake linings at municipal garage Arrow indicates accumulation of asbes- tos dust perimeter and were exposed to asbestos Fiber levels for other kinds of operations at the truck garage are given in Table 4 Boillat and Lob 1973 have reported fiber concentrations measured during drilling holes for rivets and grinding They found values ranging from 0.3 to 29.2 fibers four of the nine values exceeded 5 fibers A Comparison of Fiber Levels Visible by Light Microscopy and Electron Microscopy In the ten brake drum dust samples examined it was found that asbestos fibers shorter than 0.4 ...mpredominated Table 2 The OSHA Asbestos Standard does not require that short fibers < 5 ...min length be counted or controlled This oversight may have considerable biological significance in that small chrysotile fibers readily produce asbestos disease Holt Mills and Young 1964 1965 Davis 1965 Pott Huth and Friedrichs 1972 Wagner Berry and Timbrell 1973 122 ROHL ET AL TABLE 4 ASBESTOS Concentration During Truck Brake Service Fiber concentration Operation Distance ft Number of samples fibers Mean Range Renewing used linings by grinding Background to grinding used linings 3-5 022- 72787 022- 72787 022- 022- Beveling new linings Background to beveling new linings 3-5 512 * 512 12 512 30 1 Punching rivets into brake 3-5 2 linings Chipping rust off used brake linings 3-5 1 Sweeping floor around grinder 3-5 1 Background to sweeping 15 1 floor around grinder Fibers 5-100 ...min length counted by optical microscODY 3.8 1.5 0.8 0.2 37.3 0.6 0.4 0.3 1.5 2.4 3.6 3.1 1.7-7.0 1.2-1.7 0.6-1.0 _ 23.7-72.0 0.3-0.5 _ 1.9-2.0 _ _ _ ER materials The ashed residue was dispersed in a drop of oxygen to remove organic rubout technique nitrocellulose solution The dispersal was accomplished by a using the edge of a watch glass Nicholson Rohl and Ferrand 1971 By this method large asbestos fiber bundles are broken into their constituent smaller fibrils and large agglomerates of inorganic materials which normally obscure the of asbestos fibers are broken into particles small enough to allow virtu- presaelnlcaesbestos to be seen By placing a second slide over the ground residue and thin film is pro- ally nitrocellulose solution and then gliding the two slides apart a duced The dried film is cut into segments which are then floated off in water The film mounted onto Formvar electron microscopic grids Typically four is from each sample and one square on each grid is scanned in the grids are prepared to determine the quantity of electron microscope at 42,000x magnification chrysotile present By estimating the length and diameter of each fiber and as- suming a cylindrical fiber geometry the mass of chrysotile per grid square is determined Representative electron photomicrographs of chrysotile fibers and fibrils are shown in Figs 7 and 8 RESULTS A comparison of the optical microscopic fiber counts and the electron microscopic total asbestos mass calculations obtained from the eight samples is shown in Table 5. Figure 9 showing the same data is plotted on logarithmic paper and visual inspection indicates that a positive correlation exists between the optical and electron microscopic results although the data are limited and the amount of ASBESTOS EXPOSURE 123 FIG 7. Electron photomicrograph of air sample taken during brake drum blowing see sample No. 4 Table 5 Large numbers 70-100 of chrysotile some of which are masked by granular particulates presumably road dust 65,000 total magnification scattering precludes a regression analysis For example from these data it may be possible to predict that during the grinding of new brake linings Sample No. 8 Table 5 a worker could be exposed to about 0.5 mg of asbestos daily in circumstances in which the weighted TLV of 5 fibers would not have been exceeded Similarly Fig 9 shows that since a microgram of asbestos represents on the order of 1 million fibers per cubic meter of air of greatly varying diameters and lengths extremely high concentrations of submicroscopic fibers are present up to 65 ft away from brake repair work e.g. Sample No. 5 Table 5 even though fiber levels in such a case are barely detected if at all by the standard optical counting technique These limited data indicate that the standard OSHA optical fiber counting method may be only a fractional indicator of total asbestos exposure at least in the case of automobile repair work They also indicate that the total exposure is much higher than the OSHA technique records in terms of 124 ROHL ET AL 0.5 ... of cluster of chrysotile fibrils in background sample see FIG 8. Electronmicrograph of air sample sample No. 3 Table ) 83,000 magnification and surface area Additional studies relevant to this asbestos fiber number mass needed to confirm and extend these and other kinds of asbestos exposure are containing pulverized findings It is important to note that particles of in determination Their importance brake lining were not included in this mass terms of biologic potential is presently unknown SUMMARY AND CONCLUSIONS asbestos fiber is a major component of brake lining materials 1 Chrysotile of the lining is brought about by a combination of factors which Degradation ASBESTOS EXPOSURE 125 TABLE 5 CoUNTS COMPARISON of Optical and ElectroN MICROSCOPic Fiber Operation 1. Blowing dust off drum with air jet 10 ft away 2. Background to blowing out brake drum 10 ft away 3. Blowing dust off drum with air jet 20 ft away 4. Background to blowing out brake drum 20 ft away 5. Background to blowing out brake drum 65 ft away minutes after blowing stopped 6. Cleaning brake drum with hand brush 7. Light grindings of new linings before installation 8. Light grinding new linings before installation Optical microscopy fibers 2.0 0.3 0.4 0.8 7392 7392 7392 7392 Electron microscopy g 1.27 0.2 1.1 0.1 0.2 6.5 53.0 66.0 and shearing Modifying agents are in- include thermal stress material fatigue between the lining cluded in brake linings which lower the contbaicntdetrempypreorlaytsuirseand chrysotile fiber and wheel interface tahimsouinnttoufrnchrpyrseovteinltesfiber which survives the braking oper- dehydroxylation The factors including some which are exter- ation is related to a naunmdbqeuraloiftyadodfittihoenlailning itself As a consequence degradation for the dehydrox- nal to the properties occur at temperatures signficantly lower than that required may ylation of chrysotile with the persistence of fibers drums in New York 2 Ten samples of dust wemriectraoksecnopfyrowmas auotfomloibmiitleed bursaekfeulness ray diffracthe City and analyzed bOoptthicaclontinuous and scan modes demonstrated pres- tion analysis using all dust samples The proportion of chrysotile ranged from ence of chrysotile in This included both free fibers and about 2-15 and averaged about 3-6 Forsterite the chrysotile which survived in pulverized binder as particulates microspy 100- optical fe] - milter per Fibers 0.1 ce] 0.1 4 eo 1.0 10.0 100,0 Micrograms per cubic - elecetlerctoronn microscopy Fic 9. Comparison of optical and electron microscopic fiber counts ROHL ET AL 126 could not be unequivocally identified thermal transformation product of chrysotile by continuous scan ray diffraction in the ten dust samples was further 3 The presence of chrysotile asbestos selected area electron diffraction verified by transmission electron microscopy found both in fiber and fibril and electron microprobe analyasneds cChhermyisoctaillceowmaps osition Its frequency of occur- made by form with unaltered structure determination consistent with but lower than the quantitative diffraction rence was it should be noted that ray ray diffraction analysis However in clumps the latter would analysis is based on both free fibers and fibers present microscopic study In addition obscure the presence of discarletteerfeidbaernsdocnomepllecettreolny recrystallized fibers were also to unaltered fiber partially performed seen in the ten samples indi- Size distribution analysis at 42,000x magnification shorter than 0.4 ...min 4 of all chrysotile in fiber form is cate that about fifths be seen by optical microscopic techniques fibers are too small to brake repair work in automobile length These conducted during 5 Personal air sampling was microscopic procedures for fiber in New York City Standard optical blowing dust garages taken in the vicinity of repairmen counting were used In samples air an average concentration of 16 from automobile brake drums with compressed samples indicate that fibers was measured Backgroleuansdt 75anfdt fl roa m tphesweork site and for at least 14 measurable concentrations exist at minutes after jet air blowing at a municipal truck repair facility where 6 Personal air samplesawnedraepptlaikceantion operations are Grinding of of about 4 fibers various brake fabrication concentration brake shoes resulted in an average 37 fibers was meas- truck beveling an average fiber count of also 4,000,000 During drilling punching rivets and cleanup were ured Exposure levels during that fiber concentration gradients are measurements show During light grinding of measured Background brake repair and application work produced during truck concentrations were found 25 ft or more truck brake shoes measurable fiber beveling operations The background to 30 ft from brake work indicate that many away as well as up both automobile and truck brake measurements during workers are potentially exposed to other than brake lining employees in garages and shop management asbestos including other mechanics brake repair work were analyzed 7 Eight air samples taken during automobile correlation was found to by other optical and electron microscopy A positive total chrysotile mass calcula- counts > 5 ...mand the indicate that data exist between optical fiber These all fibers at 42,000x magnification tions based on sizing be a useful index of total free asbestos standard OSHA optical fiber counts may that the total free during brake repair work They also demonstrate is much exposure of fiber number mass and surface area in terms asbestos exposure counting techniques indicate greater than the optical fact that in addition to asbestos other biologically 8 Attention is called to the and lead compounds have been identified active substances including fcroenecesniltircaations in brake work environments are not in brake lining dusts Their known and warrant investigation ASBESTOS EXPOSURE 127 9 Potentially hazardous asbestos exposure exists during automotive brake servicing It has been reported that approximately 900,000 persons are employed in such work in the United States It is recommended that stringent industrial hygiene measures to control exposure be implemented as rapidly as possible ACKNOWLEDGMENT We thank Drs A. E. Anderson R. L. Gealer and E. Eichen of The Ford Motor Company for their valuable comments in reviewing the manuscript REFERENCES Anderson A. E. 1969 Wear in brake materials In Proc Amer Soc Metals Wear Conference Anderson A. E. Gealer R. L. McCune R. C. and Sprys J. W. 1973 emissions from - brake dynamometer tests Soc Auto Engin Meeting Detroit Michigan 14-18 May 1973. Paper No. 730549 Bark L. S. Moran D. and Percival S. J. 1975 Chemical changes in asbestos friction materials during performance review Wear 34 131 139 Bates T. F. and Comer J. J. 1957 In Proc 6th Nat'l Conf Clays and Clay Mineralogy Int Monog Sec 6 237 248 Bayer S. G. Brown T. A. and Zumwalde R. D. 1975 Document TR U.S. Department of Health Education and Welfare Public Health Service National Insitute for Occupational Safety and Health Cincinnati Ohio Berry E. 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W. 1971 A study ofthe infrared spectra ofchrysotile and related minerals In Proc Intl Conf Chemical Asbestos Minerals Louvain Univ 6-9 September 1971 paper 6 7 pp The 2nd No. Davis J. M. J. 1965 microscope studies of asbestosis in man and animals Ann N. Y. Acad Sci 132 98 111 Harries P. G. 1968 Asbestos hazards in naval shipyards Ann Occup Hyg 11 135 145 Harris A. M. 1971 The effects of grinding on the structural and thermal properties of chrysotile asbestosfibers In Proc 2nd Intl Conf Chemical Asbestos Minerals Louvain Univ 6-9 September 1971 paper No. 2A 6 pp Hatch D. 1970 Possible alternatives to asbestos as a friction material Ann Occup Hyg 13 25-29 Hickish D. E. and Knight K. L. 1970 Exposure to asbestos during brake maintenance Ann Occup Hyg 13 17 21 Hilscher W. Sethi S. Friedrichs K. H. and Pott F. 1970 Zusammenhange zwischen Asbestose and Faserl^/ngeNaturwissenschaften 57 356 Holt P. F. Mills J. and Young D. 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Zussman Ed pp 335 37A0cademic Martinez E. 1966 Chrysotile asbestos Press New York crystal structure Canadian Mining anRdelMaettiaolnlshBiuplolf6th9e 4s1u4rface42a0nd thermal properties to the Mizutani Y. Obara H. and Nakajima K. 1973 ray study of friction and asbestos Wear 23 387 392 wear of bonded Monkman L. J. 1971 Some chemical and mineralogical aspects of the acid chrysotile In Proc 2nd Intl Conf Chemical Asbestos Minerals LoduevcaoimnpoUsintiivon6-o9f September 1971 paper No. 2 9 pp Naumann A. W. and Dresher W. H. 1966 The influence of tion Amer Mineral 51 1200-1211 sample texture on chrysotile dehydra- Newhouse M. L. 1965 Epidemiology of mesothelial tumors in the London Sci 132 579-602 area Ann N. Y. Acad Nicholson W. J. Rohl A. N. and Ferrand E. F. 1971 Air pollution in New Proceedings of the Second International Clean Air York City In Eds pp 136-139 Academic Press New York Congress H. M. Englund and W. T. Berry Pott F. Huth F. and Friedrichs K. H. 1972 Tumors of rats after chrysotile and pyrene Zbl Bakt 1. Abt Orig 155 463 i.p. injection of powdered Selik2o2f-f3I8. J. Churg J. and Hammond E. C. 1964 Asbestos exposure and neoplasia JAMA 188 Selikoff I. J. Hammond E. C. and Churg J. 1968 Asbestos JAMA 204 106 112 exposure smoking and neoplasia Selikoff I. J. Nicholson W. J. and Langer A. M. 1972 Asbestos air Health 25 1-13 pollution Arch Envir Wagner J. C. Berry G. and Timbrell V. 1973 Mesotheliomata in asbestos and other materials Brit J. Cancer rats after inoculation with 28 173 Whittaker E. J. W. and Zussman J. 1956. The characterization of diffraction Min Mag 31 107 serpentine minerals by ray