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r.N VI R(IS Ml V I Al KI\tAft<l< 12, U0-12R<19?6) i t Asbestos Exposure during Brake Lining Maintenance l and Repair* .( ArthurN. Rom.. ArthurM. Lancer, MarvS. Wolff, and Irving Weisman Environmental Sciences Laboratory, Mount Sinai School of Medicine of the City University of Sew York, New York, New York 10029 . Received December 10. 1975 i 1 Data obtained on asbestos exposure of garage mechanics during brake lining maintenance and repair work show' that fiber conccntraiions frequently in excess of regulated limits ire common. The presence of chrysolite, ranging from 2 lo 15%. in brake drum dusts, was I demonstrated by X*ruy diffraction, transmission electron microscopy, selected area electron 1I diffraction, and electron microprobe analyses. Unallered chrysolile was found, both in fiber and Hbril form, in air and brake drum dusi samples. The chrysolite asbestos coment of iII personal air samples, taken during automobile brake repair work, was measured both by optical anJ electron microscopic techniques. While a positive correlation exists between the ' i types of measurements, the present technique of optically counting asbestos fibers may considerably underestimate the levels of total asbestos exposure. V withst,, I INTRODUCTION )' portion J During the past decade. significant disease risk has been found associated with L f J the inhalation of asbestos fibers in a number of occupational and environmental k: U circumstances other than in asbestos mining, milling and manufacturing, where f serious hazard was already known (Wagner el al., I960; Newhouse and -------___ Thompson, 1 Vf,S; SelikolTel al., I%4, 1965; Harries, 1968). h It rI Such exposures were found in the construction industry and in shipbuilding, as ` well as in other industrial settings where asbestos products were used. More i Phenolic J recently, asbestos exposure hits been suggested to occur during automotive brake lining repair and installation work, and measurable concentrations of asbestos y R u b he r Tire scrq Ritch < fiber were observed in the work environment of workmen involved in these opera * <i ' Cork tions (Hickish and Knight. 1970; Hatch. 1970; Boillnt and Lob, 1973). With limited ft Ci 1 son i t c data available, however, uncertainly remained regarding the type and extent of y. Cashew asbestos exposure during this work. Some investigators have questioned whether V; ,t ftnil p. free asbestos fibers survive the high temperatures produced during braking action Dryrnp (Lynch, 1968; Hickish and Knight. 1970; Hatch. 1970) contending that asbestos decomposes as a result of the high point contact temperatures produced at the s. interface of the brake drum or disc and brake lining. We have sought to obtain information concerning asbestos exposure of work a men engaged in brake lining maintenance and brake shoe installation, by analysis i \ of residual dusts recovered from brake linings and by direct measurement of the 1 This research was supported by Center Grant ES 0092$ of the National Institute of Environments! Health Sciences of the U S. IX-partment of Health, Education and Welfure. Assistance was also provided in part by the Health Research Council of the City of New York HRC U 23?9and by the Ford Minor Company. 5 no ( I . IKK Acrk'lta hfss |<k I All tt*ku s< te|skM ts Ms #h> (otth rm t*r J 8004 1954 'ice ity :nancc >ts arc s. was edron n fiber rnl of ih by cn the s may .tied with anmental g. where use and tiding, as d. More ve brake asbestos se operah limited extent of ' whether ng action asbestos d at the jf workanalysis it of the onmenta) was also the Ford A.sHt.srm KxrosiiRK 111 free asbestos fiber content of workroom air in areas where these operations take place. In the United States, tin estimated work force of at least 900.000 auto mechanics and parage 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 (Sclikoff. Nicholson, and Langcr, 1972). Asbestos in tril lion Materials In the United States, an estimated 118 million pounds of asbestos is used annu ally for the production of brake friction materials (Jacko and DuCharme, 1973). After processing (cutting, grinding, punching), the asbestos in the material sold is approximately 103 million pounds per year. In addition, asbestos contained in automotive clutch friction materials amounts to 4.5 million pounds annually. Major Constituents oj Broke l.initios 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 I. Binder. The hinders used in the automotive industry today are primarily phenolic-type resins, which arc noted for high binding efficiency and ability to withstand pyrolytic breakdown. Other materials have been used, in varying pro portions and in addition to resins, for binder improvement (Table I). 7ABI.F I (i 1 M Ml IS (.' IMH \ N I S <>t AllDMUlIU BkSM LlSIW(.** Binder ;ind or^-mic friction modilVis Fiber reinforccr Property modifier Phenolic-typc icon Rubber Tire scrap Filch Cork Gl>oniic Cavhcw nutshell resin and particles Drying oils * Chryxotilc asbestos* (grades 4-7) Unaltered Calcined Mixed fiber Lead compounds Zinc compounds Antimony oxide Iron oxide Copper metal Brass chips Clay minerals Barite (BaSO<) Wollaxlonitt (CaSiO,) Quart* (SiO,) Cryolite (Na,AIF,) Rotlenstone (SiO,) Coke (C) Coal (C) Citxonile (C) Graphite (C) Carton black (C) Molybdenum sulfide (MoS,) Fluorspar (CaF,) * See Carroll, 1967; Anderson. 1969. Anderson. 1973; Jacko and DuCharme. 197); Bark, it ol.. 1975. * Chrysolite fiber constitutes about )OCf by weight of most aulumolix-c brakes currently manufac tured in the United Slates. 8004 1955 't! *. r- ;< *OHl. ET AL. Fiber. For fiber reinforccmenl of the friction product, chrysotile asbestos is temper used almost exclusively. The mineral typically comprises from 40 to 5(XT of the brake I brake product. Fiber grades 4 through 7 are used, and occasionally, several sizes fibers. 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 arc 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." Thernn Dirr. lion at (Mg.S< Monku variat:. varialt. prolon 1957; ) which help lo "recondition" the braking surface and remove deposited decompos ition products (e.g.. rottenstone. quartz); they net as "heat sinks." reducing bin der pyrolysis and fiber decomposition thereby extending the useful life of the lining (e.g.. brass chips, metals, etc.). In gcn incipk be ha v chry s; Il is important lo nolo 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 dchydroxylation and recrystulliz^ition ofehrysolile asbes Atud\ M tos at high temperatures) which may accumulate on the surface of the brake lining 'let. The hardness of the forstentc (hardness 6.5-7.0) is such that it lends to score and Optica. gouge brake drums and discs (hardness 3--3.5). degrading them prematurely. scant-.; Therefore, recrystallization of chrysotile to forsterite is an unwanted effect, hin deleft. dered insofar as possible by the modifiers present in the matrix. Op; Mule rials of Biological Interest - Asbestos, quartz, and heavy metals are constituents of automotive brake lin ings. each warranling special consideration from the viewpoint of biological activ ity. The focus of this report is limited to the problem of chrysotile asbestos exposure. Ma luinistns of Degradation of Brake Linings during Use Brake wear is dependent upon many factors, such as the temperature generated t. C. * detect spoil*, chrysi bintlc: Obsct; X-r all dr sampl at the surface of the brake shoe during braking operations. At any one time, only a son u small percentage of the rubbing area is in contact with the wheel, with "hot spots" generated, ranging up to MX) to IOOOC (Carroll. 1962; Anderson. 1969). Il is not uncommon during moderate braking action, to attain temperatures as high as siXkC (Carroll. IW>2). Some investigators have suggested that, in addition to bin der pyrolysis, chrysotile completely dehydroxylates under these conditions and k k occur comp were presc. tcchr. "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 X-ray diffraction, chrysotile in brake materials displays structural strain and substructure fragmentation, caused by shear during braking processes (Mizutuni et at., 1973). This shear strain produces material fatigue which, with hinder pyrolysis, can cause brake lining disintegration at t. T. * i k Ulcr.t: Tr. 1 w, Aulorr ftiaintc i the tin 8004 1956 'tile asbestos is 'I to 50% of the y. several sizes Mies. >n products are Med in Table 1. increase brake pressures (e.g.. xnt of friction .1 compounds); and enhancing d ``abrasives,'' ted dccompos' reducing binful life of the ng agents is to t in the brake rysotile asbes brake lining, s to score and prematurelyed effect, hin- :ive brake lin- ologicul activotile asbestos ) ure generated e time, only a h "hot spots" 969). It is not -s as high as klition to binmditions and . 1962). Howsscs, besides dation. (Burar have been ike materials shear during ices material teyration at \ A ASM.SKIS tXPlISlRF. ' 113 temperatures far hehne those reipdred for chrysotile dehydroxylation. Therefore, brake lining disintegration may liberate partially altered, or unaltered, chrvsotile fibers. " Thermal Decomposition of Chrysotile Differential thermal analysis indicates that chrysotile undergoes dehydroxyla tion ai 650 to 6X0C and rccrvstallizcs (anhydrous magnesium silicate to forsterite) (Mg,SiO,)nt about 810 to X20C (e.g.. Martinez. 1966: Daykin. 1971; Berry. 1971; Monknian. 1971; Harris, 1971). These temperature ranges are subject to great variation as a function of the chemistry of the fiber, particle size, instrumental variations, sample packing, etc. Also, forsterite has been noted to form, during prolonged static heating, at considerably lower temperatures (Bates and Comer. 1957; Martinez. 1966; Brindley and Hayami. 1965; Naumann and Dresher. 1966). In general, temperatures in excess of 57()C are required for dehydroxylation and 'ncipient forsterite formation in chrysotile. Extensive study of both the thermal behavior of chrysotile and brake lining composition and design indicates that chrysotile fiber may survive in the decomposed lining dust. METHODS . Analysis of Broke Drum Dust (De composed Lininp) Ten samples of automobile brake drum dusts were collected and examined by Optical microscopy. X-ray diffraction, transmission electron microscopy and scanning electron microscopy with microchcmical capability, for the purpose of determining the presence or absence of chrysotile.2 Optical microscopy, employing polarized light, was generally not useful for detecting asbestos in brake drum dust. A number of factors are considered re sponsible for this phenomenon including the low relief and birefringence of chrysotile and the nature of the matrix, consisting largely of road dust, resin binder, and pyroly/ed residue, which, in optical microscopic preparations, readily obscures the smaller asbestos fibers. X-ray diffractometry. in the continuous and step-scan mode, was performed on dusts. Chrysotile reflections (hkl = 002; 020; 004) were observed in all ten samples. Quantitative determination of chrysotile content was made by compari son of unknowns with calibrations of chrysotile dilution standards. The weight occurrence ranged from about 2-159), with an average ranging from 3--6%. Lead Compounds, quartz, calcite. mica, clays, barite, graphite, and alpha-iron particles were identified as well. In several samples, weak, diffuse reflections suggested the presence of forsterite, bul positive identification could not be made using this technique. Identification of Chrysotile hy Electron Microscopy Transmission electron microscopy, selected area electron diffraction, and elec- ' We ^knowledge the cooperation of the United Automobile Workert. Local Union No. nd the Automobile Dealer* Industrial Relations Association in helping us obtaJn these samples in auto ttantenance in the New York *rea Lach sample was liken from "a typical job" under way at the lime. 8004 1957 \ iron microprobc 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. I). Selected area elec tron 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 inlrafibril displacement (Figs. 2A, B). Occa sionally, fibers were observed without characteristic chrysotile morphology, with mottled surfaces and obliterated fibrils, indicating partial or complete recrystalli?ation. Flection diffraction patterns obtained from these particles displayed I! iI I * fu.. I. KtesUonphoiomicrogf.iph or Ijiye chrysolite handle in brake drum dust (JH.000 x m|tnif>calion) Olhcf panicles include pin-mil resin hinder *nd mud dusl debris. polycr rings I rochcti to pusbundle margin Frc< <2,000 small t in lent: optic;.: jet. fo, were f ureme. Using 22.000 were I. and t)t vs 42, data n ich of the ten panicles in a trysotile fiber led area eleceservation of ite reflections -A. B). Occa- 'holopy, with ie recrystallies displayed I A.NHt.S'ins hXI'OSL'Rk 115 i Pic. 2. Selected rea electron diffraction patterns obtained on fiberx of chrysotile obtained during air sampling a! brake repair shops. In A, the reciprocal a axis is marked a* as are the layer lines in the (Okll senes. Indexing of upper nght quadrant yielded 16 reflections corresponding to single crystal X-ray diffraction analysis of Whittaker and Zussman. 1956. Pattern in (B) displays "smearing" of reflections in a clockwise" manner suggesting inlerplanar rotation. - polycrystullinc characteristics of multiple random reflections or Debye-Scherrer rings rather than the distinctive single fiber chrysotile patlem (Fig. 2B). Mic rochemical analysis with a probe technique on the unaltered fibers showed them to possess the usual Mg:Si ratio of chrysotile. In addition to free chrysotile fiber bundles and fibrils, chrysotile was also frequently observed projecting from the margins of binder fragmcnls (Fig. 3). Free asbestos fibers present in the decomposed lining dusts were sized at 42,000x magnification. The results, seen in T able 2, show that most fibers arc too smulFto be seen by optical microscopy; almost alt of them are shorter than 0.4 pun in length; virtually all arc of respirable size (-5 ^m). Halch (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 m length category, while only 6% were longer than 5 ;im. Jaeko and DuCharme (1973) made size distribution meas urements 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 gm in length and that 60%> were longer than 0.5 gnt, Some discrepancies between our data and those of Jacko and DuCharme may be attributed to their use of the lower magnification (22.(XX)x vs 42.000x.). at which fibers shorter than 0.20 prm may 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 8004 1959 jOl i '% * *' -5 / .i i /* ttr. i j t v * Ii ii .4i* .i ii i? i* i x ii *. \r. J ii it j, f t i t I > air s: from were whic Ash, At repa: mini sunt; aeeo Safe ii (Mas ing I 'I Hirer corn fit.. 3. Klcciron photomicrographs of brake drum dusts. Chrysolite ts present in both free fiber and fibnl form Opaque jnanular material is road dust or phenolic binder, t. x 10,800. b. *9300; C. *30.000; d *3o.(xx>. jr W rep!; hue k re pa ard i indicate ihiti the chrysolite fiber population generated by brake wear is a strongly i New 4 skewed one. vs ith almost all fibers concentrated in the smaller than 5 pirn region. ^ aft ci J No attempt was made to si/e the asbestos-binder particulates. I' opet Personal Air Sampling during lirake Repair Work j and Personal air sampling for asbestos exposure during brake lining maintenance : area and repair was carried out at franchised auto dealer garages, (axi fleet repair . air I' t shops, and a municipal truck repair shop, all located in New York City.' Personal y by > prat! `Assistant r ill pnivl(lni|i tip|kiiliiinly tut s.iiiipliuy mas pisen by the Dcfculim-nl r Ait Kcsouncs. Nc* Voik C'uy. v: \ it! (ii'n it \ I 1 rvl. jA ' i.vl 4- ; * .-fjt >n\<1 ft. :t Hbtr nr,J : *>0.000; Wrongly region. enance repair rsonal 'urctj, ASRKSTOS f XPOSl'Rt 117 TABl.F. 2 LtM.in I)i\miM'iiov mi Chi\mihu Pint** iv Brakc Drum Dust* <*>1 7So l SouA, tsixi- ::miA ::sn- soooA 3000 - 3750A Total 1 Sample r;i <r-;t (%> (%) 11 2 p3 4 5? 5 KH `F. 6 17 9 r. 10 4\20 20 26 527} so 29 6 11 :34 ii j 32 :s 25 37 26 17 4 9 12 26 21 30 41 - . 2IS1 6 31 II 96 87 -- 70 7 96 -- 78 12 56 2 99 17 97 `10 75 31 79 * * :Fibers counted and sized at 42.000 nil fibers have diameters from 250 to 500A. air samples were taken during and after brake repair work and at varying distances from the work sites in other arcus of the garages and shops. The latter samples werc intended to provide information concerning levels of asbestos exposure 2 which garage employees other than those doing brake work might experience. Ashfsios Exposure Jiiriup Aitl<innihilc Rrakc Repair Work Air samples were first taken in the breathing 2onc of mechanics 'doing brake repair work. These peak exposure measurements were taken over periods of ?-8 minutes during which the wankers were blowing dust from brake drums. The air * samples, taken on membrane filters, were processed, and fiber counts made in accordance with the proccdutes which have been adopted by the Occupational Safety and Health Administration (OSHA) of the U.S. Department of l-abor (Bavcr. Brow n, and /.umwalde. 1975). F.ssentially. the analysis consists of count ing fibers 5 to 100 ^m. in a fiscd area of a Porton graticule, using phase contrast microscopy at a magnification of 400x . This microscopic method enhances image contrast and allows large asbestos fibers to be readily seen and counted. When a vehicle is brought into a repair shop for brake lining inspection or replacement, the wheel is removed and h>osc dust is removed from the drums and back plates, generally by means of a compressed air jet. A recent survey of brake I hrpitir establishments in Baltimore and Washington revealed that this is the stand \ ard method in those cities (Caslleman ct t//.. 1975). A similar situation exists in New York City. The cloud of dust that is produced is visible for several minutes afterw-uids (Fig. 4). Tahle 3 shows that fiber concentrations are high in the operators area under these conditions (an average concentration of 16 fibers/ml), 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 fi 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 fibcrx/ml or more, longer than 5 nm, as 8004 1961 M8 ROMt 7 AL. :V -* Jpf r r UU>. - BacJs If. at [t ' f Ur l Fit.. 4. Removal of Oust from brake drum and back plate by pneumatic air blowing at automobile garage. a time-weighted average for workers, and concentrations above 2 fibers/ml will be illegal after 1976. Regulations set a peak concentration (maximum excursion) of 10 fibcrs/ml of air. Newly proposed standards are designed to set a limit of 0.5 fibcrs/ml (500.000 fibers/m'), with a maximum excursion of 5 fibcr^ml. It Wits generally found that there was minimal, if any, effort to control dust in most garages. Workmen do not use respiratory protection. There was little aware ness of the potential hazard of brake dust. ' In a single instance, brake drum cleaning was not done with a compressed air jet. but with a dry hand brush. Fiber concentrations were somewhat less (2.5 fihcrs/ml) at the operator level, but background levels 12 ft away were the same as with air jet denning. Asbestos Exposure during Truck Broke Repair and Installation Work Personal air sampling was also conducted at the New York Department of Sanitation truck repair shop, where various kinds of brake application and repair work are performed. Used truck brake linings are salvaged by grinding the surface to remove grease and dirt, and new linings are ground to expedite break-in. The edges of new linings arc beveled on a grinding wheel or arcing machine to avoid noise problems. (Fig. 5). Holes are drilled or punched into the brake lining, which * t;: r p. i rX4 k r P fc.* 'k' V" t. ic if. ir i -. " v*. r< l Cie;tdr bt ---b-i-; -F M in HS *ng ir < 3 ,. is th done persi brak. in th cent: cone of sb brak-. in tli fiber the ; s.im; 8004 1962 at automobile 'ml will he sion) of 10 mil of 0.5 I. rol dust in tic aware- Tressed air i less (2.5 ic same as rtmenl of md repair ic surface k-in. The to avoid ig. which ASM.VI OS KXHOSt'KK 119 TABl.K 3 A sat shiv C<in< t s i > a t ions in kim. Aiiomohii t Bxxxr St avicr Operation Blowing dust out of brake drums with compressed air .jet Background samples taken t varying distance and lapsed times, .ifter brake drum blou mg Distance (ft) Number of samples 3-5 5-10 10- 70 4 j 2 Distance from operation tfn Time lapse (min) 10 0 :o 0 12 5 SO 5 65 7 75 M Fiber concentration (fiber^mt) Mean Range 16.0 h.h-29.8 3.3 2.0-4.: 2.6 0.4-4.8 Concentration (OberVml) 0.3 08 0.2 0.1 0.1 0.1 Distance Number of Fiber concentration . (fibervml) tfu sample* Mean Kange Cleaning brake drums with dry brush Background sample's taken 3 minuies after cleaning brake drums with drv brush 1-2 i: 2 2.5 1.3-3.6 3 0.1 0- 0.2 Fibers 5- 100 in length, counted by optical microscopy. * The new proposed Asbestos Standard of the U. S. Department of Labor records asbestos exposure in fibtrs'm', noting that a workman might respire approximately 8 m* of air per w-orking day. retain ing an unstudied proportion ttf inhaled fibers. The above table omits reference to air content of fibers c 5 rm in length. s 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 (l;ig. b), an average peak concentration of about 4 fibers/ml was found in the breathing zone of the operator. The data show that measurable liber con centrations are found 25 ft or more away. At a distance of 25 ft. for example, a concentration of I fiber'ml (1.000.000 ftbers/ml5) 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 t)f the operator. The average of five air samples was about 37 fibers/ml. Area samples, taken up to 30 ft assay from this operation, demonstrated (he presence of airborne fibers. It was of interest to note that, at the lime of this sampling, from eight to 15 other garage mechanics were working within this 8004 1963 -/I A 'Jr m KOHL IT At. < . <. i9 f > i 4 A. Fio. 5. Be vtlifif of truck brake linings a! 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 tire given in Table 4. Boillui 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 fibcrs/ml; four of the nine values exceeded 5 fibers/ml. A Comparison of Fiber Levels Visible by Lipbt Microscopy and Electron Microscopy In the ten brake drum dust samples examined, it was found that asbestos fibers shoncr than 0.4 gin predominated (Table 2). The OSHA Asbestos Standard does not require that short fibers 5 pm in 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, 19t).s; I'oti. Hath, and Friedrichs. 1972; Wagner, Berry and Timbrell, 1973; V' c< kr. t fv *if. Fn Hil.sc impo: The SCOpi'. oppo: optic: select taken corde grind. Frepii One dust s 8004 1964 l,.,; -. * * * ^ 3 ^ J * .c. . - *Vv i 4 * I t- M .*> j. 1 ->H of *jt>CS- bcrations d during 3 10 29.2 >s fibers rd does d. This ry sot ile !. 1965; I. 1973; Hilscher ft of, 1970). Atlcntion has recently been again called lo the potential importance of this question (Bouhuys, I97.S). There is little published information on the numbers of. and sizes of, submicroscopic asbestos fibers in occupational exposures. The present study afforded an Opportunity to collect data on the relationship between submicroscopically- and optically-visible fibers for this specific industrial exposure. Eight air samples were selected for both light and electron microscopic examination. Six of these were taken during brake drum dust removal operations with optical Tiber counts re corded from 0.1 lo y.h fibers/ntl. The other two samples were taken during light grinding of automobile brake shoes. Preparation and Analysis of Air Samples One square centimeter sections of the eight membrane filters were mounted, dust side down, on microscopic slides and ashed in low icmpcralnrc netivated 8004 1965 t. i I  4/ r if i j 122 kohl Hal. TABLE 4 Asm s i ns Coni :i.niiaimhw Di'iivc Taucx Easier. Sravicr 1 pittance Number of Fiber concentration (fiberVml) Operation (ft) samples Mean Range Renewing used linings by grinding Background to grinding used linings Beveling new linings Background lo beveling new linings Punching rivets inio brake linings Chipping rust off used brjke linings Sweeping floor around grinder Hackground (it sweeping fltmr around grinder 3-5 10 25 60 3-5 t i: 30 3-5 3-5 3-5 15 to 3. 1.7-7.0 2 I.J 1.2- 1.7 2 O.S 0.6- 1.0 1 0.2 -- 5 37.3 '23.7-72.0 1 0.6 _ 2 0.4 0.J-0.J 1 0.3 _ 2 1.5 1.9- 2.0 1 2.4 -- 1 3.6 -- 1 3.1 Fibers S-IIKl ^m in length. counted by optica) microscopy. oxygen to temove organic materials. The ashed residue was dispersed in a drop of nitrocellulose solution. The dispersal was accomplished by a "rubout" technique using the edge of a watch glass (Nicholson, Rohl and Ferrand. 1971). By (his method large asbestos fiber bundles are broken into their constituent smaller fibrils and large agglomerates of inorganic materials, which normally obscure the presence of asbestos fibers, arc broken into particles small enough to allow virtu ally all asbestos to be seen. By placing a second slide over the ground residue and nitrocellulose solution and then gliding the two slides apart, a thin film is pro duced. The dried film is cut into segments which are then floated off in water. The film is mounted onto Formvar-coatcd electron microscopic grids. Typically, four grids arc prepared from each sample and one square on each grid is scanned in the electron microscope at 42,lH>0x magnification to determine the quantity of 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 arc shown in Figs. 7 and K. RESULTS A comparison of the optical microscopic fiber counts and the electron micro scopic tola) asbestos mass calculations obtained from the eight samples is shown m T abic- y Figure V, 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 (- F - i I * l V ti,- 5 t> 8004 1966 i. t r; if: I k f F: No. laies seal pos Tab cun exc< on i anti up t fibc cou fibc sm < toll. <;inc 7-7.0 :-i.7 f. - 1.0 72.0 '-0.5 '-2.0 I Pr-,' ASRK.VmS JXI'OSt'KK ;i!23 - i ! .}. f Jrop of hnique itv this '.mailer lire the v vinuluc and is proer. The y. four J in the lily of ind asuarc is rs and micro own in :r. and ptical aunt of la is. Fi< . 7. Lleclron photomicrograph of air simple taken during brake drum blowing (see sample No. 4 . Table 5). Large numbers (70-100) of chrysoiile. some of which are masked by granular panicuUtej, prejumahly 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 cir cumstances in which the time-weighted TLV of 5 fibers/ml would not have been exceeded. Similarly. Fig. 9 shows that, since a microgram of asbestos represents on the order of I million fibers pci 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 (c.g.. Sample No. 5. Table 5). even though fiber levels in such a case arc 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 expo sure, 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 $004 1967 K *t '. .! ;f ` j' ' i- :l i ' I t T 4 I i \ jit i 1. Blowtr 2. Biickf, 3. Bhtwir. * B^ick^s 3. Backer minim** Clcami 7* l.ight >.* 8. Lipht , i Fk.. R. ElecUonmicrograph of air ampl< of clutter of chrysotiie fibril* in backfround sample (see sample No. 3, Table 3) (R3,000x ma|nific*(ion). asbestos fiber number, mass, and surface area. Additional studies relevant to this and other kinds of asbestos exposure arc needed to confirm and extend these findings. It is important to note that particles of asbestos-containing pulvcriwd brake lining were not included in this mass determination. Their importance, in terms of biologic potential, is presently unknown. SUMMARY AND CONCLUSIONS (I) Chrysotiie asbestos fiber is a major component of brake lining materials. Degradation of the lining is brought about by a combination of factors, which i 4 f. `V (' % ji 2, 8004 1968 include eluded i and h, dehydro ation is nal to th niay net* ylation ( (2) Te C'ity. at; tion ana ence of about 2 chrysoti ASHt.VIOS rXIMISOlU - 125 TABt.i: .< ` If ('llWI'AKIVIN (It Ol'IK SI (VII Kill IKIIV Mil C ><l( 1 (Mil. PlM* CotMS ( )pcrllHn Optical microscopy (Hbers/ml) Electron microscopy (^p/m*) I. Blowing Jus! oft Jriiiu wilh air jel (10 ft away) 2.0 1.27 Background !o blowing oul brake drum (10 ft away) 3. Blowing duvl off drum wilh air jet t-0 ft away) 0.3 0.2 0.4 M 4- Background to blowing oul brake drum (20 ft away) 5. Background to blowing out brake drum (65 ft away--7 0.8 0.1 minutes afler hlowing slopped) Cleaning brake drum with hand brush Light grindings of new linings before installation fc- Light grinding new linings before installation .1 0.2 3.6 6.5 4.7 53.0 2.7 66.0 - include thermal stress, material fatigue, and shearing. Modifying agents are in cluded in brake linings which lower the contact temperature between the lining and wheel interface; this, in turn, prevents binder pyrolysis and chrysotile fiber dchydroxylation. The amount of chrysotile fiber which survives the braking oper ation is related to a number of additional factors, including some which tire exter nal to the properties and quality of the lining itself. As a consequence, degradation may occur at temperatures signficantly low er than that required for the dchydrox ylation of chrysotile, with the persistence of fibers. (2) Ten samples of dust were taken from automobile brake drums in New York City, and analyzed. Optical microscopy was of limited usefulness. X-ray diffrac tion analysis, using both continuous and step-scan modes demonstrated the pres ence of chrysotile in all dust samples. The proportion of chrysotile ranged from about 2-15%, and averaged about ?-6Cf. This included both free fibers and chrysotile which survived in pulverized hinder as particulates. Forsteritc, the . ..fx 5i it I* /- * i> 4' v; i It to this id these Ivcrized ;tnce, in aterials. >, which .1 Km.. V (.'ompariwm of optical and electron microscopic fiber counts. 8004 1969 i *. i- >V *- 1*1 ,ftj^rv i '*"* #**** * * r .r r ! r' n i ^illi fft j l 1 126 KOHL T At thermal transformation product of chrysotile could not he unequivocally identified by continuous scan X-ray diffraction. (3) The presence of chrysotile asbestos in the ten dust samples was further verified by transmission electron microscopy, selected area electron diffraction and electron mieroprobc analyses. Chrysotile was found, both in Tiber and fibril f k (9) Rotenh servicing. It i in such work hygiene men- form, with unaltered structure and chemical composition. Its frequency of occur *{ rence was consistent with, but lower than the quantitative determination made by Wc thank Dr- X-ray diffraction analysis. However, it should be noted that X-ray diffraction analysis is based on both free fibers and fibers present in clumps: the latter would valuable eonmic obscure the presence of discrete fibers on electron microscopic study. In addition to unajtcred fiber, partially altered and completely recrystullized fibers were also Anderson. A K seen. Anderson. A I. bmkv if\ mi> / (4) Size distribution analysis at 42.000x magnification in the ten samples indi No. cate that about four-fifths of all chrysotile, in fiber form, is shorter than 0.4 ^m in Bark, L. S.. M j length. These fibers are too small to be seen by optical microscopic techniques. (5) Persona! air sampling was conducted during brake repair work in automobile mjiicri.iis \l Bates. T I-' . ;,n Sec ft. ;3' i garages in New York City. Standard optical microscopic procedures for fiber Bayer. S. C. . f. I counting were used. In samples taken in Ihe vicinity of repairmen blowing dust Health. I ah I from automobile brake drums with compressed air. an average concentration of 16 and I Icalih t I nbcrs/ml was measured. Background and time-lapse samples indicate that measurable concentrations exist at least 75 ft from the work site and for at least 14 Berry, f- I 11> In I'tiv Wl. p.irv: minutes after jet air blowing. Boill.n. Ms. ((>) Personal air samples were taken at a municipal truck repair facility where brake luuiu. various brake fabrication and application operations are performed. Grinding of Bouhuyv A if I truck brake shoes resulted in an average concentration of about 4 ftbers/ml Brindley. C, W <4,(XXi.(XXVm'). During beveling, tin average fiber count of 37 fiberCml was meas ured. Rxpostirc levels during drilling, punching rivets, and cleanup were also serpentine Burv ell. J [ i Carroll, W (, i measured. Backgiound measurements show that fiber concentration gradients are Castl cm.in, H . produced during truck brake icpair and application work. Dat ing light grinding of ha/auU tl truck brake shoes, measurable fiber concentrations were found 25 ft or more Daykm. (\ W i I away, as w-ell as up to 30 ft from brake beveling operations. The background Inti (`on! > 7:h. 7 pp measurements, during both automobile and truck brake work, indicate that many Davis. J. M ; I employees in garages other than brake lining workers are potentially exposed to At oil. /, asbestos, including other mechanics and shop management. Harries. \* { t (7| Right air samples taken dating automobile brake repair work were analyzed Harris, A M t (if by other optical and electron microscopy. A positive correlation was found to September exist between optical fiber counts ( > 5 ^m) and the total chrysotile mass calcula Hatch. O. (iv" tions based on sizing all fibers at 42.000x magnification. These data indicate that standard (OSH A) optical fiber counts may be a useful index of total free asbestos exposure during brake repair work. They also demonstrate that the total free Hickish. n. t Onnr H. Hilscher, W . ** II asbestos exposure, in terms of fiber number, mass, and surface area is much greater than the optical counting techniques indicate. and Holt, P. F.. M,: i 1 (K) Attention is called to the fact that in addition to asbestos, other biologically active substances, including free silica and lead compounds, have been identified in brake lining dusts. Their concentrations in brake work environments are not lung. J. /'>> Holt. r. K . M Import.inw. Jacko. M (t .. . known, and warrant investigation. clutch luu*'. */ I 8004 1970 illy identified was further n ilil'I'rartion >er and fibril icv uf occuran made by diffraction latter would In addition "s were also imples indi n 0.4 n m in iechniques. automobile es for fiber owing dust lation of 16 Jicaic that - at least 14 ilitv where grinding of 4 fibers/ml was meas- were also adients arc grinding of ft or more .ic kground that many exposed to e analyzed s found to ss ealeula- licatc that ,, asbestos total free i is much ologically ' identified ;s arc not r I i ,ir ,'A .' 4 1 k \ s. ASBI.MIW I.XI'IISCRI 127 (9) Potentially hazardous asbestos exposure exists during automotive brake servicing. It has been reported that approximately 900,000 persons are employed n Stich work in the United States. It is recommended that stringent industrial hygiene measures to eontiol exposure be implemented as rapidly as possible. ACKNOWLEDGMENT "t thank Drv A t.. Anderson. R 1. Gr.ilcr. and E Lichen of The Ford Motor Company for their Valuable ciiinrnonls in icvicwing ihc mniiuscnpl. REFERENCES Anderson. A. B . IIVAV), Hmr m bruit- imiii'riuh. In PuK. Amer. Soc. MelaJx Weir Conference. Anderson. A. E.. (Icaler. R. I. . McCone. R C.. and Sprys. J. W. (1973). Ashesw, emission, from broke thnantomeier tests. Sv. Auto login. Meeting..Detroit. Michigan. 14-JK May, 197.V Paper No. 7M^49 * L. S.. Moran. I) . and Peicival. S J Chemical changes in a*hcslos-ba*ed friction rr li I c r i; 11 v during per Idrmancc -- a review. Wear 34. |\|-I39. Ba,C5T f and Conici. J ) 11 sis 7) in hoc. bih N.il'IConf, Clays and Clay Mineralogy. Ini. Monof. Sec 6. S. Ci.. Brown. I A., and /iiinwaldc. R. I). (1W7M. IXk/umcnt 1R-M. U.S. Department of Hcallh. Edu cation .ind Welfate. fhihlic He.ilth Service. National Insiluic for Occupational Safety and Health. (`me mnati. Ohio crry. h. h. (19*111 7hi rant I itnalvsis nf various t hr\ \ttfiles usiny evolved * aler analysis let hnit/nes. 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V * If f r r * > l e i f * r4 * ' . i / V tSVIKMwit Man-.M \ M 4'/ M;in\ Other hu power, i placed ii, In expoi in the In future h devclopi ant) irrI: authms t cal nt.il. trypan,*' altered com u* I fmnnci *1 Nine arlel'.ie I CX[V,!tc: the hi,*n COlinli i, theme iheaith s providit evaliinir irrigate, eluding health <. shown ' Control! niun-m. frequen The t diffeivn medic ii 8004 1972