Document O1M94yQmNRd4Kxx0oMgOwjqZX

?HiC* 10'.< f.;ATR I A.S STANDASDS 11ST I T^T , .-j ( Oily 15, 1976 To: Asbestos Study Committee Subject: Mount Sinai (Dr. A. K. Rohl) Paper: "Asbestos Exposure during Brake Lining Maintenance and Repair11 On February 6, 1976, I advised the Asbestos Study Conwiitee that t had received a paper entitled "Asbestos exposure during brake lining main tenance end repair" from Dr. A, Af. Boh) of Mount Sinai* You may refer to my February 6, 1976 covering letter* I have now received from Dr. Rohl copies of page proofs of that article as it v;i11 appear, Dr. ftohl believes, in the August 1976 issue of Environmental Research, This is essentially the same paper presented by Dr. Rohl at the May 1974 meeting of the American Conference of Governmental industrial Hygienists (AtfSfK). ft has been up-dated and expended to include papers in 1974-75 for re"e^ence. ir, reviewing this, I do not believe his figures include fiber counts of asbestos longer than 5 microns on an S hour time weighted average (TIM) basis. The emphasis continues to be turning to asbestos fibers shorter than 5 microns and their measurement by other than optical microscopy. E. \h Dr i si ana Executive Director \ P-FMSI. 0C3H PLAINTIFFS WV-06046 ao o io > :o ^'.khco inj/j mNjvvnogiANir 1 5 j it * \ I I <i!i i aj( 1 I i i <i i T V t \ }' r - M 12. JltMJI *19161 * frcx? ' i Asbestos Exposure during Brake Lining Maintenance and Repair' Authw N. RoHU Arthur M. Lakcck. MariS. Wutrr. asti IftVS.N'C WdSMAN Stiencn Lahornwr). AIohoj Stool Srhool 6//itttfirmr of UmvrnUy of X>' >*i, >ei. A> Vftri 10019 Ctty Received Oec-mber ID. 1975 Data or asbrne* *ipe*ur* of ;sq^ mechnoict during brake lining mamteftbAet , and repair iho* chat fiber coneemrsciom frceucmly rsettt alyetaw* kmtti are common- The pnssme o! eftiyvaire. nnjmg from i 10 IS*. in brake drum 6tmt, wtt acmcmuraied by X-ray difFmetien, transmtftueft election miaoop). arierted areaelctiroa diftractioe. and eteetftrn mieeopretK analym. Unaltered eftrytotit; wa fesuW. bh to fioer and fibril tc*rm. t ab and brake drum dtut sample*. The chrysolite aiteuM content uf persona) ar samples. taken during automobile brake repair wait. was c*aored boxH by optical and electron mereeop<e teebnictuee. WWe a (Wi correlation smt* between the lypei nl measurements. the present technique of piicahy coumj; atrevo* fioen mas roPStdesoWy uAfiarcsdrame the level* of total aebeaioe exjK*tvs. ** 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 alrcadv known (Wagner ei <i!.. I960: Newhouse and Thompson. 1965; SelikofT a!., 1964, 1965: Harries. I96S). Such exposures were found In the construction industry and i shrpbufld/ng, 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 (Hicktsh and Knight, J970( Hatch, 1970; Boillat and Dob. 19751. With limited data available. However, uncertainty remained regarding the type Mid extent of asbestos exposure during this work. Some investigators have questioned whether free asbeyos fibers survive the high temperatures produced during braking action (Lynch, 1968: Hiekish and Knight. J970; Hatch. 1970) contending that asbestos decomposes as a result of the high .pain? contact temperatures produced at the interface of the brake drum or disc and br3ke lining. We have sought to obtain information concerning asbestos exposure of work men engaged in brake lining maintenance and brake shoe installation, by analysts of residual dusts recovered from brake fmtogs unci by direct measurement of the *( I t 'THi* research wa supported by Cemer Oram ES M97R t the Xi*unn1 of Fftvw>nsemj* Hold* Science* fthe i/.S. Dcpunnwnt of Health. Education aJ \n chore. A\*Kt.inre nets at* I pnwtjrd if* part b> On Heafth ftswareh CwuocU ol the C*y of New Yml tIKC U and by ite i FwJ Motor Company. * \ C -*b* V> A^iV"*: TV(-. l*. r lf> ktifa i+isi'J no j tufwwn Assofswws/ K.rft Asidta -S35 ' vL I. V/. Suils 4D2 Hisi::v:?ACZr D, C. 2CCSS r5 hud'..' m free asbestos fiber content of workroom sir in areas where these operations take place- In the United States, an estimated work force of at least 9W>,0OP auto mechanics and garage workers is potentially exposed to asbestos in the servicing of both brake and clutch liftings. Furthermore, much brake dust enters the general environment during automobile use (Jacko ami DuCharme. 1973). to add more to the burden of asbestos air pollution (SelikofF, Nicholson, and Langcr, 1972). Asbestos in Friction AItttrrtah In the United States, an estimated ! 1S million pounds of asbestos is used annu ally forth* production of brake friction materials (Jocko and DuChnrme. 1973). After processing (cutnng. 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 Constituent* ofBrake 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* ificr). These are listed in Table, U Binder. The binders used in the automotive industry today sgt primarily phenolic-type resins, which are 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 1). TABLE t CoiiMosi Cfro*fc*-r o* At'Tc^tOTivi Bkauc Ltvrve** fimiler onJ orpnie frkuen mtxJifieri Fiber reinforcer Property modifier Pnervobc-type reiio Rubber Ti/e &er*p Pitch Cert; GilMtcme Cfethew nurihel] retie *1 panicle? Dryr{ elb Chrysolite itshrttos* |prad;> A-?} Uealicred Cakirred htued Tiber Lead compound* 2"tc compound* Aiummax* exiCe Iren side Copper metal Bratt chip* Cb>> mineral* Bartte tBaSO.t WeliasreAite (CaSiOj) Cryolite INa,Alrtt Buticmuxte tSiOj) CokeC> CeJiCl G^>onite (C? Graphite (C> CarKui Hack (Ct SMjhJeiujm >utfi4e (MoSj Fltavsfui iCaF.i * Sr<Cur#.*n. tWJ; AeUcrtun, i96*>; Arlcr*on. TjckoandtJoCtemre. 1"?ML.rk./,. IVT5- * Ov> .nil- f,tvi cyn-Jnuw>. stnnn 5i>" hj uetjtii ot *kw automvMhc Nut.ev curremi) rruiwfj.-. u<*d to the ItaticU Stairs jromicir 1 ttt ' it Fibr/- For fiber reinforcement of the friction product. chrysorile asbestos is ' used exclusively. The mineral typically comprises from *10 to 505r of the brake product. Fiber grades 4 through 7 are used, and occasionally, several siies- arc 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 !. Modifiers are used for a number of purposes; they are included to increase brake It 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 compountfs); 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 decompos- ition products (e.g.. rouenstone. junrt2): they act as "heat sinks,'* reducing bin der pyrolysis and fiber decomposition thereby extending the useful life of rite lining (e.g., brass chips, metals, etc.). It is important to note that one msyor purpose of the rtcondutoning agents is to retard the formation of forsierite (a mineral not originally present in the brake material, but created by dehydroxylation and recrystalIizarionofchrysorile asbes tos a? high rempurtuures) vhlch may accumulateon the surface offhe brake luring. The hardness of the forstcrits {Mohs. 6.5-7.0) is such that it tends to score and gouge brake drums and discs (hardness 3-3.5), degrading them prematurely. Tnsrcfore. recrystallization of chrysmile to forsierite is an unwanted effect, hin dered insofar us possible by the modifiers present in the matrix. Materialg of Biological Interest Asbestos. quari2- .and heavy metals are constituents of automotive brake lin ings, each warranting special consideration from the viewpoint of biologies! activ ity. 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 rime, only a small percentage of the rubbing area is in contact with the wheel, with "hot spots" generated, ranging up to 800 to JG00"C (Carroll. >962; Anderson. 1969). It is not uncommon dunng moderate "btaking action, to artam temperatures sv,hrgh as 5>3*C (Carroll. 1962), Some investigators have suggested tiui. m addition to bin der pyrolysis, chrysotile completely dehydroxyhues under these conditions and |a'reduces to powder*' where it is swept off the broke facing <Cam>H, 1962). How* ever, Ihi? hypothesis is oversimplified, in that olher important processes.' besides .theema} wear, contribute to shoe breakdown, and brake shoe degradation. (Bur* .well. 1957). For example, the effects of abrasive wear and macroshear have been mvesrignted. When monitored by X-ray diffraction, chrysotile in brake materials 'displays structural strain and substructure fragmentation, caused by shear during broking processes (Mi/niani et ul.. l9Tjy This shear strain produces material fatigue which, with binder pyrolysis, can cmiir brake fining dishiirgrmionttt r iENVIRONS NTAt RESEARCH end C Y N lC O lO G iC O N C G tO G l Currtroii i m ' temperatures far hehw those irquiredfur chrystuile dehydroiyiath/tt. Therefore, brake lining disintegration may liberals partially altered, or unaltered. chrvsatite fibers. Thermal Decomposition ofChrysolite Differential thermal onalysK indicates that chrysodte undergoes dehydroxyte- uon at 650 to fiSO'C and recrystaJlizex (anhydrous magnesium Silicate to forsterhe) (Mg-SiO,) at about 810 to 820*0 <e.6-. Martinez, 1966: Daykin. 1971; Berry, >571: Monkman. 1971: Harris, 1970. These temperature range& are subject to great variation as a function of the chemistry of the fiber, panicle 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; Martinsi. 1966; Brindley and Nayami. 1965: Naamaaaaod Dresher. 19661. In general, temperatures in excess of 370*0 are required for dehydroxylotion and incipient forsterite formation in chrysolite. Extensive study of both the thermal behavior of chrysolite and brake lining composition and design indicates that chrysolite fiber may survive in the decomposed lining dust. METHODS ~ Annfysts ofBrake Drum Dust {Decomposed Lining) 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 microchemical capability. for the purpose of determining the presence or absence of chrysolite.* 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 ami birefringence of chrysolite and the nature of the matrix, consisting largely of road dust, resin binder, and pyroiyjed residue, which, in optical microscopic: preparations, readily obscures the'smaller asbestos fibers. X-ray difTraciomecry. *n the continuous and stcp-scan mode, was performed on Mi dusts. Chrysolite reflections (hki 002. 020; 004) were observed in all icn_ samples. Quantitative determination of chrysolite content was made by compari son of unknowns with calibrations of chrysolite dilution standards. The weight occurrence ranged from about 2-1559, with an average ranging from 3-6Lead compounds, quartz, calcite. mica, clays, barite, graphite, and alpha-iron panicles were identified as well In several samples, weak, diffuse reflections suggested the presence of forsterite. but positive identification could not be made using this technique. Identification of ChnsotHc by Electron Microscopy Transmission electron microscopy, selected area electron diffraction, and etec- JW swkm>sWJyv fh* Ci**p?n*ii<w7 frf ifcc Unfletl AuitvixthU? Wiwkfu, Lvu! ltam Ket, 254 ihe AinMTH>hili. CWuk'fN IpkImMiuiI kct.nms AsNnti.rtkm in K:ipn^ wv otum lh.se *,impU* in avu' mstmro.uw? 4hk>j*< the Sew York jic*. Ewh hampk* was token Irtvis "u y job*' umic? oyy ai Ih: time. U r; vi^m n*0 . ; ' ifur, mteroptoK; analysis of the brake dusts were carried oul Oft ejtfh or Ihe isn" s&fflplo after preparation by a technique which disperses the dust particles in a - nitfocetifc*< film without ateer/nf panfete fize disiributipn. Free chrysolite fibsr- bundles and fibrils were observed in all ten samples (Fig. \). Selected area elec tron diffrocimn analysis of representative fibers demonstrated the preservation of the chrysolite structure {Figs. 2A. B). Some patterns displayed arettaic reflections suggestive of mierfitorfl rotation and imraflbrii displacement {Figs. 2A, B). Occa sionally. fibers were observed without characteristic chrysotiie morphology, with mottled surfaces and obliterated fibrils, indicating partial or complete recrystaliization, Electron diffraction patterns obtained from these particles displayed ie jt Fiu. l. if Lirjfc chf'sv-.lW Kmjtf i Nuke Jrwm <iiU {XS.fiNO* nvipnifkia- in>n) CNN' furtik> hcUu'>* ptofek fxn twvf ro.wf <u>t Jvftris. i Fie. Z. 5eteeieC area eteeiren diffraction patierns o&takirti on fibeti f chrysolite obutincd earing aw tam^in; at brake tejwir ahttps. in A, the reciprocal a ri* h marked a* *< are the Inter tines in the (OKU senes lmierin? of spper rifhi piuulran! ietki) 16 rcftcciii'm etfresponding to ample crystal X*ra diffraction anjj i-*. gf Whiu-Acr a4 Tusimao. FuturnmiSr tiispljy* *meai< tft|" of refWetbn* in a '*}oci.wtte'' manner iu{pesiin; kuerplAnar mtatkm. polycrystaltine characteristics of multiple random reflections or Debye* Seherrer rings rather than the distinctive single fiber chrysolite pattern ("Fig. 2B). Wic* rochemtcal analysis with a probe technique on the unaltered fibers showed them to possess the* usual Mg:Si ratio of chrysolite, in addition to free chrysolite Tiber bundles and fibrils, chrysolite was also frequently observed projecting from the margins of binder fragments (Fig. , Free asbestos fibers present in the decomposed lining dusts were sized at 42.Q00x magnification. The results*, seen in Table 2. show that most fibers ore too small to be seen by optical microscopy; almost all of them are shorter than 0.4 nm in length: virtually alt are of respirable size (-3 *tm3. Hatch 0970) in reporting on . optical fiber counts obtained fiom brake cleaning operations with compressed air jet, found that 94% of the fibers fell in the 2-3 pm length category* while only 6% were longer than 5 /tm. Jacko and DuCharme (1973) made sire distribution meas* urements of asbestos fibers in brake dusts generated during dynamometer tests. using both optical and electron microscopy. They found, at magnifications of 22,00fix that 30% of the fibers were from 0.25 to 0.50 jim in length and that fitY7e were longer than 0.5 Mm. Some cltscrepnncics between our data ami those ofincko and DuCharme may be Attributed to their use or the lower magnification (22.000x vs 42.000x). at w hich fibers shorter limit 0.20 ;itn may nut he easily seen cw identified on the electron microscopic screen. Thus, both the optical fiber Cs<uiu data in otter studies and the electron microscopic fiber sue distribution dam Ii t ' IrrwvKu^it- "** ' j 1 -\ : * ` < i 1 i < ) t tI i < j i4I * { I Hk*\*SSi - *\w ^m&zzfrr, ^;i^is?35sgaaas,- I t!* <s* .** *>5s ' h*- V .. .$Hs * t'^g* j^SrQ* ^ - a****! *, *4* ^O O 'O ^lN iO 108*3*38 WN3ftH08lAN3 F>c. 3, Electron pK^ccnicrofrBphj of braVe drum 8su. Cfefysetito is p*cM in boft Itw Fiber bed fihrit lorm ~Op3quc yrptfy'iwtcrttf% to*i 0w ffrjrwlir.brndst.**- aJO^OO: b. *M0fc c. x&onfttf. *3Q.0. ------ , indicate that the chrysotile fiber population generated by broke wear is a strongly skewed one, with almost oil fibers concentrated in the swatter than $ ftm region Ho attempt was made to size the asbestos-binder paniculates. Persnnnl Air Sampling during Pmke Rfpfii' Work Personal air sampling for asbestos exposure during brake lining maintenance and repair was carried out i franchised auto dealer parages, taxi Reel repair shops, and a rmmtojxiJ micfc repair shop, all taeritcd i Hew York City.' Personal i JA*'txivtf in p*vi*bj opfvrm.i>i> f*w iwfwn? svp\tfi l*s ihc PeiMfiiwiM W Air R*vTte. N* Yoii Cuy. : !.. . ! I g Ir.ur.iiotM r ' r1J m* Ta&lE: l_> vctii D)ii*vi>av of Cnb^vmiii F<*i ' *' fii u.t D*vm D* *r* Sample ?jo-iinoA H (> 1500-223OA wmi 22*0-3ft*U N <*l JV`-37S0A nm TetaJ 1 40 \4 II Tl 96 2 32 23 37 -- S7 1 20 23 23 _ 70 " 4 26 37 26 ? 9i 5 57 17 4 -- 78 . 6U 9 n 12 36 7 50 26 21 2 99 t 29 30 21 i? 97 96 41 it to 73 to M 6 Si 32 ___ * 3slbcn caume and tiled Mi 42,030*; mti {fesn have dtameten (raa 230 (fi 303ik. sir 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. Th: 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 Broke Repair tV'ork Air samples were first taken in the breathing zone of mechanics doing brake repair work. These peak exposure measurements were taken over periods ofJ-S minutes during which the workers were Wowing dust from brake drums. The air samples, taken on membrane filters, were processed, and fiber counts made in accordance with the procedures which base been adopted by the Occupational Safety and Health Administration (OSHA) of the U.S. Department of Labor (Bayer. Brow n, and ZumwaUSe- 1975), Essentially, the analysis consists of count* ins fibers 5 to 100 in a fixed area of a Ponon 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 loose dust is removed from the drums and back plates, generally by means of a compressed airjet. A recent survey ofbrake repair establishments in Baltimore and Washington revealed that this is the stand ard method in those cities (Cattleman ei aft, 1975k A similar situation exists in New York City. The cloud of dust tnut is produced is visible for several minutes afterwards (Fig. 4>. Table 3 shows that fiber concernrations are high in the operator's area under these conditions (an average concentration of 16 fibervm!;, and that there are significant concentrations a! least 20 ft sway. 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 enn be exposed. Current (interim) regula tions of OSHA prohibit concentrations of5 fihcr&'ml or more, longer than 5 ;m. as (f :m 1 f i 4 *1 ui 1' S N V lR O N M tN fA i RtSCARCM .ul GYNCCOtOGIC O N C O tO C t Fig. 4. Removal f dutf fmm fef*V;c dmm an* fek plMt fey pfirUftMi? Vf fetewtnj u taianwfe&r a time-weighted average tor worker*, and concentmeions above 2 fiberx/'ml will bt illegal after 1976. Regulations set a peak concernration (maximum excursion) of !0 fibers'ml of air. Newly proposed standards are designed > set a limit of 0.5 fibers/ml {500.000 fibers/m1!. with a maximum excursion of 5 fibers'ml. It was generally found th3t there was minimal, if any. effort to control dust in most garages. Workmen do not use respiratory proteclion. There was little aware ness of the potential hazard of brake dust. fcnt*s*ngte mstwiee, trrofce dram 'droning -was not -done-wit!*-* Compressed-Air jet. but whh a dry hand brush. Finer concentrations were somewhat kss (U fibers/ml) at the operator level, but background levels 12 ft away were the same as with atrjet cleaning. Asbestos Exposure timing Truck Rmkc Repair and InsioUaiUm U'ori Personal atr sampling ww 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 br.ike linings are salvaged by grinding the surface to remove grease and dirt, ami new linings arc ground to expedite break-in. The edges of new linings arc beveled on a giimhny wheel or arcing machine to avoid noi.e problems, (Fig. 5}. Holes ate di tiled or punched into the brake lining, which I t. < rvenitu > M M l A\a>u TABLE ) Si MO Operation Slotting dust owl At br*U drums Mmp'tutd a }ci Dittwee fft) 3-5 5-10 !0- Number at iamp>*> 4 3 2 Fiber concentration fAtftrvmn .Mub Ranpe UO k 6-3*4 3.3 J.ft-4.2 2.6 0*-4.8 Distance bom operation Chi Timt lapse f<nin) Concentration ff*enuml) BxcVjrourwf samples uteri 10 0 0.3 *1 varying distance and 20 t 04 lapsed limes. after brake i: 3 (L2 rum lowest SO J d.\ t' 7 0.1 It 0.1 Dtuaoec Humber of Fiber toncenrratien tvpfrtmn (ft) xamptes Mean Rang* bnfre Aram* wttfc dry bru*h lUckprounO samples taken 3 rrumtie* after cic*nmj bn>We drums i:h 6ey bru%h t-3 12 2 2.1 tJ--3.6 3 O.i 0-0.5 * Fiber* 5- 100 m in lt*cth, counted b oprkal nicrOieopj. * The weu> AsStwoi$>V4*ixt4 o*'be \i. S. tJefianmem rf \_obv>frecord*>b*uo* expnore i AhetVrB*. tiaimf ifcnt a wo/Umn miphi revere approximately tt m* fair per arkrn$ day, retain ing an tm*rvtl*eJ proportion of inhaled fihrrs. Tbs atxwe taWt mm reference to air content of Abort < S *m in knp:h. s ............ .... j1 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 iht results of personal air sampling in the course of this work. During light grinding of truck brake shoes (Ktg. .fo.aa.average.peak conuemratiotvofabout-Offorrshfli wgstound iA the breathing tone of the operaio:. The data show that measurable fiber eon* corurations are found 25 ft or mure away. At a distance of 25 ft, for example, a concentration of 1 fibcr/ml O.pOO.QUO fibers/ml was found. Much larger numbers of shorter.fibers would simultaneously be inhaled. During the beveling of w\cfc brake shoes on a grinding machine, very high concertrracrons of fibers were found in the vicinity of the operator. The average of air samples was about 37 ftbers/mS. Area samples, taken up u> 30 ft away from this operation, demonstrated the presence of airborne fibers. 2{ was of interest to note that, at the lime of this sampling, from cighi to |5 other garage mechanics were working within this t.tv 'ir;r.ttt l >v i j ij ! I 1 < $ i } \ i RESEARCH o*<J CYNECCHOCIC ONCOVOOY Pit. 5. Revcirn; 9f iruck brtfce iinwp ai municipal fvagi. Arrow Miouei aceumulatkin of ubefttot perimeter and <*? exposed asbestos. Fibsr levels for other kinds ofoperations at the truck garage anrgrvetvTnTsWe--*. Boillai ami Lob (Wft have reported fiber concentrations tneasitred during drilling holes for rivets and grinding. They found values ranging from 0.3 co 29.2 I fibers/ml: four of the nine values exceeded S fibenUmi A Comparison of Fiber Levels Visible by Ugh Microscopy and Geeiron Micros` Copy In the ten brake drum dust samples examined, i? was f<H>nd that asbcsios fibers Shoner than 0.4 >*m predominated (Table 21. The 05HA A<be>tos Stamford does i>w requite that short fibers l< 5 Aim in length) l*c counted or controlled. This oversight may have considerable biological significance in that small chrysolite fibers readily produce asbestos disease |HoH. Mill'. :md Swine. 19M. i%5; Ditvis. 1965; Kt. Utah, and Frierfiichsu f?72; U'agucr. Berry ntidrimbtcli. !W: CO )i i i i i * Htlscher ei a!.. 1970). Attention has recently been acorn called lo the potently importance'of this question (Soubuys. 1975). There n^tttte 'pubSshed 4rrformattw-o the cambersaL and sizes of. submicro* scopi: asbestos fibers in occupations* exposures. The present study afforded *n opportunity to collect tinta on the relationship between submkrroscopicsli)'- rmd optically*visible fibers for this specific industrial exposure. Eight air samples were selected for both light and electron microscopic cxsiminatron. Six of these were talien during brake drum dust removal operations with optical fiber counts re* corded from 0.1 to 3.6 fibers'ml. The other tw samples were taken during light grinding of automobile brake shoes. Prtpartiiion and Analysts ofAir Samples One square centimeter sections of the eight membrane filters were mounted, dust side down, on microscopic slides and ashed in Uw temperature activated :o; yv( ;m r/iMXMt>4TAl RfSfAfiCH iC O K W O DIOOICOWAO Pun W W l'^ l* 1ViW9W}4CWlAN1 r i i I i < t < j ii f i i -n- v ! TAftj.C A**' Cv .s*v*o> Oib*c 1m\ B*vm Btvticr* Operatitm DitUMK* ff4> Number e? Fiber ft<radt> (fiberv'mil Mean Ra*j* Bite*mp used liiwop by fnnm$ Bscs$reu:ia io ;nndm; used hnmgi Beselmp ne Uuin* BickprewoJ to Mveimj Of*- jtiunp Punehint riven j brake linmsv dumping rusf off uKti bntke Iminst Soeepinf tow round pnndtf* Bsf^snauoa to sweecBTtf Am; &rund grinder 3-A 10 23 W> 3-y S tz 3D )-} 3-3 3-5 15 JO 3.8 0-7.0 m U 0-0 3 0.8 0.6-1.0 I 0.2 -- i 37.3 23.7-73.0 l 0.6 -- 2 0< 0.3-03 1 0.3 -- 2 1S 1.9-2.0 J 2.< DHW t 36 ****** ! 3.1 Fibers 3-IOO ttm ip length. counted by optical microteaer. oxygen to remove organic materials. The ashed residue was dispersed in a drop of nitrocellulose >o!uton. The dispersal was accomplished by a'mboot*' technique using the edge of a watch glass (Nicholson, Rohl and Femmd, 1971). By this methovl targe asbestos fiber bundles ait broken into their constituent smaller fibrils and large agglomerates of inorganic materials, which normally obscure the presence of asbestos fibers, are 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 ofTin water. The film is mounted onto Formvar-conted electron microscopic grids. Typically, four grids are prepared from each sample and one square on each grid is scanned in the electron microscope at 42.00fix magnification to determine the quantity of xfer^scuilr.present. ..By^sdmaimg Ibr length and diameter of each fiber, ami as-_ suming a cylindrical fiber geometry', the mass of chrysolite per grid square is determined. Representative electron photomicrographs of chrysolite fibers ami fibrils are shown in Figs. 7 and 8. RESULTS A comparison of the optical microscopic fiber counts and the electron micro scopic total asbestos mass calculations obtained from the eight samples U shown in Table 5. Figure 9, showing ihe same data, is plotted on logarithmic paper, nnd visual inspection indicates that a positive correlation exists between ihe optical ami electron microscopic results, ait)tough fie data arc Jimbed ami the ammmt of. i J... . rurv. ,ii i 1 i it iI l I Fc, ?. HirtJfon phoionfcftffninh of -w wmplf Li<* Uuun- brake dnm bWinpIvae No. 4. TaNe SK Larye numbers (7(WJOO) of eferyMXttc. umr of which are masked by pnuiiiUr f<amcu- taiei, pmiumaNy raaJ tfusf <6$.Ctf)0 total nujmificni'oni scattering precludes a regression analysis. For example, from these data it tnay be "pwsibie xtrpnsdret-Thai. dorms the srmding'of'new 'brafce fmKTgs-fSnmpfcr* No. <, Table 51. 3 worker eould be exposed to about 0.5 mg of asbestos dairy in cir cumstances in which the time-weighted TLV of 5 fiben'ml would not have been exceeded. Similarly, Fig. 9 shows thy. since a microgixim of asbestos represents on the order of I million fibers per cubic meter of air (of greatly varying diameters and lengths), extremely high concentrations of sttbnneroscopic fibers nre present up to 65 ft nwny from brake repair work <c.g., Sample No. 5. Table 5>. even though fiber levels in such a case are barely delected, if at all, by the standard optical counting technique. These limited data indicate that the standard (OSH Al optical finer counting method may be only a fractional indicator of total asbestos expo sure. at toast in the cate of automobile repair work. They also indicate that the total exposure is much higher than the OSHA technique records, in terms of .!.................................................... ! COe'/'riti * i> I \ 1 CNWRONMlt i \ M RESEARCH Iuac CYNICOlOGtC OtfCOlOGY ?&, 5 EkMsnHHnknvnph 1 aa s^pk ofeWwer f ehrysoiit* flHrtU in hackprwnfl Uih-*s lire MW?> Nu. J. TatsSs > <53.WO* . *, >- 1< asbestos fiber number..mass, ami surface area. Additional studies relevant to this and other kinds of asbestos exposure are needed to confirm and extend these findings, it is important to note that panicles of asbestos`Containing pulverized brake lining were not included in this mass determination. Their importance, in terms of biologic potential. t presently unknnwn. SUMMARY AND CONCLUSIONS (U Chrysolite nshesurs fiber is a major component of brake lining materials. Degradation of the lining is_b> ought about b> a combination of fi*cmt>, which i* ' ^ cor* wait ^ ... .... pit m TABLE S nr OrncAt .< Euciens Mier*orn Pie Cm si. Operation Opi/saf microscopy (fiUcrv'mh flecww? jruCrosccfvy l ), Bowing Uvw i&efum wiiftotf>ei 110 It awa>) 2.P 1.27 2 tackgroorwl to Wowing Out brake drum 110 fs a.ay) 8.3 0.2 3. Blowing Uw*t of? Crum with ait jet t?f) It sway) G.fi t.l 4, Background id Wowing but brake drum (Z& h *w>y) OS 0J }. Background lobUtwing out brake drum (6* h *wy--t minutei after Wowing tiopped* .1 02 4 peantet Brake drum with luni bru$h 3* L2 7. Light pnr>Jinj of nr* lining* before i*Kiaflat>oa 4.7 n.o & Light grinding re** tiningj before iMijIution 2,7 M.C include fhermaf stress, ma/erta! fatigue, and shearing. Modifying agents are in* eluded in brake imines which lower the contact temperature between the lining ami wheel interface; this, in turn, prevents binder pyrolysis and chrysolite fiber dchydro\vlation. The amount of chrysolite fiber which survives the braking per* anon is related to a number of additional factors, including some which are tx\cr* nnl to the properties and quality of the Iminy itself. As a consequence, degradation may occur at temperatures signficantly lower than That required for ihe dehydrox* ytaiion of chrysolite. with the persistence of fibers. (2) Ten samples of dust were mVcn from automobile bmke drums in New York City, ami analyzed, Optical microscopy was of limited usefulness. X-rav diffrac tion anah'sh. using both awwiftuous and step-scan modes demoimreted the presemre of chrysolite in all dust samples. The proportion of chrysolite ranged from about 2-15%. and averaged about 3~65. This included both free fibers nnd chrysolite which survived in pulverized binder as particulates. Forstente, the t i t Fu.. 9 CCffKlOHI e e e e OJi t pti;.0 ;ui,l <IiVkb nwmw:*pic fivi counts thermal transformation product of chrysolite could not be unequivocally identified by commuuns scan X*ray diffraction. - o> The, presence of chrysolite asbestos in the ten dust samples was further verified by transmission electron microscopy, selected area electron diffractw ami electron nilcroprobe analyses. Chrysolite was found, both m fiber and fibril form, with unaltered structure and chemical composition. Us frequency of occur*^ rence wax consistent with, but lower than the quantitative tfeterminalien mads by 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 obscure the presence of discrete fibers on electron microscopic study. In addition to unaltered fiber, partial!) altered and completely reerystzUized fibers were also seen. H> Size distribution analysis at 42.00Ox magnification in the teosaasphn fadI? cate that about four-fifths of all chrysolite. in fiber form, is shorter than 0.4 #tm in length. These fibers arc too small to b? seen by optical microscopic techniques. <5> Personal air sampling was conducted daring brake repair work in automobile garages in New York Cuy. Standard optical microscopic procedures for fiber counting were used, in .samples taken in the vicinity of repairmen blowing dust from automobile brake drum* with compressed air. an average concentration of 16 fibers.'ml was measured. Background and time-lapse samples indicate that measurable concentrations exist at least 75 ft from the worksite and for at least M minutes afterjet air blowing. (6) Personal air samples were taken at a municipal track repair facility where various brake fabrication and application operations are performed. Grinding of truck brake shoes resulted in an average concentration of about 4 fibers/ml <4.(XKUXXVmJ). During beveling, an average fiber count of 37 filwrsfmi wu meas ured. Exposure levels during drilling, punching rivets, and cleanup were also measured. Background measurements show that fiber concentration gradients are produced during truck brake repair ami application work. During light grinding ef track brake shoes, measurable fiber concentrations were found 25 ft or more away, as well as up to 30 ft from brake bfvding operations. The background measurements. during both automobile and truck brake work, indicate that many employees in garages other than brake lining workers are potentially exposed to asbestos, including other mechanics and shop management. (7.1 Eight air samples taken during automobile brake repair work were analyzed by other optical and electron microscopy. A positive correlation was found to exist between optical fiber counts l>^ym) and the lotnl chrysolite mass calcula tions based on sizing all fibers at 42.000x magnification. These data indicate that standard {OS HA) optical fiber counts may be a useful index of total free asbestos exposure during brake repair work. They also demonstrate that the total free asbestos exposure, in terms of fiber number, mass, nod surface area is much greater than the optical counting techniques indicate. (Si 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 Their concentrations in brake work environments arc not known, and warrant investigation. . i i i i 111 ~ (9) Potentially hanriUnji axbesios exposuie exist* during automotive brake semcmg. li ha* been reported that approxtmuicl5 9JKMKW person* 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 rhank On. A. E. AoUenecu ft. L. Dealer. vti t. 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