Document MoM2YO82M6y00yaJx9q4d1wjz

DownloadSearchable PDFRandom document
ASBESTOS INFORMATION ASSOCIATION NORTH AMERICA 1835 K Street, N.W., Washington, D.C. 20006 (202) 223-4885 22 July 1976 Memorandum For: Subject: John Marsh John Riopelle ,0~-- ~~~ Erich Feierabend Edward R. Zacharias Advance of Mt. Sinai School of Medicine Article on Brake Lining Maintenance and Repair Attached galley proof of article prepared by Mt. Sinai School of Medicine (N.Y.) staff and scheduled to appear in the August issue Environmental Research and Gynecologic Oncology is forwarded as a matter of interest. This study was cited as the primary reference for the NIOSH "alert" issued August 1975 (distributed to members) calling attention to potential health hazards to workers exposed to asbestos dust during servicing of brake and clutch assemblies. The "alert" received nation-wide publicity. Ed Drislane, executive director, Friction Materials Standards Institu~e, was advised by Dr. Selikoff that the brake lining repair aspect of the asbestos-health question is going to become a major project." We are seeing increasing evidence to substantiate that remark. Mr. Drislane's memorandum on subject to FMSI 7 asbestos study committee is also attached. Attention is invited to the AIA/NA leaflet, "Asbestos and Brake Linings" and the apparent need to review this publication in the interests of current and positive addressal to subject. Your comments will be appreciated. H. Mereness Executive Director cc: ~es Armstrong, Stan Christian, Bendix Corp. ~- W. Drislane, FMSI Enclosures FMSI 06786 l : J1HCtiON MATERIALS STANDARDS INSTITUTE, INC., E-210 ROUTE 4, PARAMUS, N, J. 07652 l July 15, 1976 To: ~sbestos Study Committee Subject: Mount Sinai (Dr. A. N. Rohl) Paper: "Asbestos Exposure during Brake Lining Maintenance and Repair 11 On February 6, 1976, I advised the Asbestos Study Committee that I had received a paper entitled "Asbestos exposure during brake lining maintenance and repair" from Dr. A. N. Rohl 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 will appear, Dr. Rohl 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 (AGGIH). It has been up-dated and expanded to include papers in 1974-75 for reference, In review~ng: this, I do not believe his figures include fiber counts of asbestos lo[;ger than 5 microns on an 8 hou~ time weighted average (TWA) basis. The emphasis continues to be turning to asbestos fibers shorter than 5 microns and their measurement by other than optical microscopy. nm/erc Enc: E. \"J. Dr i slane Executive Director FMSI 06787 ]"'. .j ,.. .,.,.r'irJ~b-.y1 #1.17? .. :J .1".'1:1'1/I.CJo ... ]. ' ..I.. . I _t, : TtX I ! Asbestos Exposure during Brake Lining Maintenance and Repair1 ARTHCR N. RauL, ARTHUR M. LANCER, MARYS. WoLFF, ANn IRVI~C \VEISMAN E;;virmrmental Science., Lahoratory, Mount Sinai Srlrool of Medidne of the City Uniwrsity of Nt>w York. Ne,; rark, Ne-.. l"ork /0029 Receiv.:d Dec.:mber 10, 1975 r I ' Data obtained on asbestos exposure of garage mechanics during brake lining m:~intcnance and repair work show that fiber concentrations frequently in excess of regulated limits are common. The presence of chry~otilc. r~nging from 2 'to 15%, in br:Jke drum dusts, was demonstrated by X-ray diffmction. transmission electron mic:fl'Scopy. sek::ted are:J electron diffraction. and electron microprobe analyses. Unaltered chrysotilc was fc-und. both in fibt:r and fibril form. in air and brake drum <lust samples. The chr}sotile asbestos content of p;:r~nal air samples, taken during automobik brake repair wurk. WitS r.:easurcd both by optical :Jnd electron microscopic techniques. While a positive cw-rcbtion :::.~i~ts b.:tween the lypes of m~asurements. the present technique of optically counting a;t>~stos fibers may consiJaably underestimate the lc\'els of total asbestos expt>sure. 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 a~1d manufacturing. when! serious hazard was already known (\Vagnc1 et a/., 1960: Newhouse and Thompson, 1965; Selikoff eta/., 196-L 1965; Harries, 1968). Such exposures were found in the construction im.lustry and in shipbui!Jing, as well as in other industrial settings where asbestos products were used. More recently. asbestos exposure h:-~s been suggested to occur during automotive brake lining repair and installation work, and measurable concentr::~tions of asbestos zm fiber were observed in the work environment of workmen involved in these opera- ~ :;o tions (Hickish and Knight, 1970; Hatch, 1970; Boillat and Lob, 1973). With limited 0z data available, however, uncertainty remained regarding the type and extent of ~ mz };:' asbestos exposure during this work. Some investigators have questioned whether free asbestos fibers survive the high temperatures produced during braking action .- (Lynch, 1968; Hicl,ish and Knight, 1970; Hatch, 1970) contending that asbestos :;;o m decomposes as a result of the high point cor:tact temperatures produced at the tJ< m interface of the brake drum or disc and brake lining. }>- :;o n We have sought to obtain information concerning asbestos exposure of work- ::r: men engaged in brake lining maintenance and brake shoe installation. hy analysis c :> r::.. of residual dusts recovered from brake linings and by direct measurement of the !I . () .z-.<. () 0gl ri I ~I 0ol ~L 1Thi, r~s~;m:h w:~~ supported by Centt:r (iran I ES (109:'~ of the :--;;:tion::l ln,ti:L:t<." of Fn\'ir<>nmental Ho:.tlth S-.:it:nn:;; of the U.S. D~partm.:nt uf H.:;1lth. Etlucatinn :.nJ \\'elf'''" .\-'i>t . n,.:- wa' aho pr.>vi,k,l in p:1rt P] the H::alth R"'"arch Council tf th" City <>f ;-.;;:" York II RC li :'J2\l <~ml by th:! Ford Motor Comp:wy. ! I110 I r:.:.;::_:;!r}) HT~:'.~!-PQN ASS!}l}LUlON/ N~. t!1 .!\n:~~dc~ ! ~S35 { \; ~ .- :t d. \"1. Suite ~-t02 \~:5::i~ :~"!icr:, D. C, 200CD =-~-=~----~------------------------------ FMSI 06788 Ill free asbestos tiber content of workroom air in areas where these opcmtions take? place. In the United States, an estimated work force of at least 900,000 auto mechanics 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). AI> bestos in Friction M Merials In the United States, an estimated 118 million pounds of asbestos is used annually 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 ciutch friction materials amounts to 4.5 million pounds annually. Major Constituents of Brake Linings ' A number of materials is commonly used in the manuf."tcture of the three major automotive brake lining components (binder, fiber reinforcer, and proper1y modifier). These are listed in Table l. Binder. The binders used in the automotive industry today 2;e primaril}' phenolic-type resins, which are noted for high binding efficiency and ability to withstand pyrolytic breakdown. Other materials have been used. in varying pro-,p-o-rt-io-n-s-a-n-d--in-a-d-d-iti-on- -tor-es-i-ns,-fo-r--b-i-nd-e-r- im- pr-o-v-em..e.n-t -(-T-ab-le-1). ------1 I TABLE I Co~1~10:-< CoMtosons OF .-'t.Lro,IOTJ\"E BRAKE LtsJ-:G~~ BinJer anJ ors:mic fricrion moJifiers Fiber reinforcer Prop~rty modifier Phenotic-typ.! re~in Rubber Tire scrap Pitch Cor).; Gilsunite Cashew nutshell resin and particks Chrysnfil<! ashcstos~ (grades 4- 7) Unallo::red Calcined Mixed llt>er Lead compounJs Zinc comp<.'unJ> Antinwny o:-.id.: Iron oxide Copper metal Bras~ chips Clay minerals Barite (BaSO.l Drying oils Wollastonite (CaSiO,) Quartz IS!O,~ Cryolite r:-:a.AIF,l Rottenstone (SiO,) Coke (C) Coal!Cl Gihooite CCJ Graphile (Cl Cart>''" t>bd; ICI ~h'l}llJcnum ~t.:flcte (MoS~) Flll<'f~[>.tr ICaF,I s~.: Carr<>ll. l<lf.~: .-\nd<>h<>n. 196'l: An,krson. l<l? .1: J:.d-.<1 :HlJ DuCh:trruc. 111?.\. ll:.rl...<t of.. l'J-:"5. ~ Chry,l'lik llh.:r .:on,Jilut.:-; :lh>ul 50:; h~ \\.:i);ht ,,f ""''[ :lllh.llllc>li'c f,rak.:~ cur:.:ntly m.wufa..:- lllred in the UnilcJ Slal.:s. FMSI 06789 I.I I J: ~ w< rw.l) I..X... z~ w g~z 5z w "Uc: 0 d .0.... 0uz 0 u cg:5 0uzw >0 'I l_ ' zrn :S ;;o z0 ~ zm ~ r- :;>:> m V> m ' ;p. :0 (') I 0 :J I I 0.. C) -z< m (') 0 5 C) n n:0z 0 r -09r1 112 i. i Fiber. For fiber reinforcement of the friction product. chrysotile asbestos is us.:d almlhl exclu~ive\y. The mineral typically comprises from 40 to 50% of the -brake pruJuct. Fiber grades 4 through 7 are used. and occasionally, several sizesare admixet.l or even calcined to improve performance ch;tr;~cteristics. Modifiers. Perhaps the wit.lest range of materials used in friction products are the property modifiers. Nineteen representative compound~ are listed in Table I. 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 ret.luce 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 intemal"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 m<\ior purpose of the reconditioning agents is to retard the formation of forsterite (a mineral not originally present in the brake material. but created by de hydroxylation and recrystallization ofthrysotile asbestos at high temperatures) which may accumubte on the surface of the brake lining. The hardness of the forstcritc (l\tohs. 6.5-7.0) is such that it tends to score and gouge brake dmms 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 lntaesr Asbestos, quartz. and heavy metals are constituents of automotive brake lin- ings, each warranting special consideration from the viewpoint ofbioll1gical activity. The focus of this report is limited to the problem of chrysotile asbestos exposure. Meclwnisms of Dtgradation of Brake Linings during Use Brake wear is dependc:nt 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 \vheel. with "hot spots" generated. ranging up to 800 to 1000C (Carroll, 1962; Anderson. 1969). It is not uncommon during moderate braking action, to attain temperatures as high as 500,C (Carroll. 1962). Sollie ir.vest:~ators have suggested th<lt, in addition to bin.der 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 1hat other important processes: besides .thermal wear, contribute to sh0e breakdown, and brake shoe degradation. (Bur- :well. 1957). For example. th~ effects of ahrasive we~r ami macroshear have been 'investigated. When monitored br X-ray diffraction. chrysotile in brake materials 'displays structural strain and subqru-::turc fragmentation. causeJ by shear during br;.king rru.::cs-;cs (\lizut;\ni et of.. J97J). This shear stmin produces materi:ll .jrc,~,""" . ~.fatigu.: which, with hinder pyrulysi,;. can cause brake lini11g disintegratio11 at FMS\ 06790 113 temperaltlres far beloll' those required for chry.wtile de hydroxylation. Th<!reforc, brake lining disintcgr::llion may liberate partially altered, or unaltered, chrysotile -fibers. Thermal Decomposition of Chry.wti/e Differential thermal analysis indicates that chrysotile undergoes dehydroxylation at 650 to 630~C and recrystallizes (anhydrous magnesium "Silicate to forsterite) (~lg~Si04) at about 810 to 8:!0C (e.g. t-.fartinez, 1966; Daykin. 1971; Berry, 1971; Monkman. 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; l\hrtinez. 1966; Brindley and Hayami. 1965; Naumann and Dresher, 1966). In general. temperatures in excess of 570,C are required for dehydroxylation and incipient forstcrite formation in chrysotile. Extensive study of both the thermal behavior of chrysotile anJ brake lining composition and design indicates that chrysotile fiber may survive in the decomposed lining dust. METHODS Analysis of Brake 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 mi-:roscopy with microchemical capability, for the purpose of detl!rmining the presence or absence of chrysotik.2 Optical microscopy. employing polarized light, was generally not useful for detecting asbestos in brake drum dust. A number of factors are considered responsible fL1r this phenomenon including the low relief and birefringence of chrysotile and the nature of the matrix. consisting largely of road dust, r.:=sin binder, and pyro1yzeu residue. which, in optical microscopic preparations, re<tdily obscures the smaller asbestos fibers. X-ray diffractometry. in the continuous and step-scan mode, was performed on ali dusts. Chrysotile renections (hkl = 002; 020~ 004) were observed in all ten samples. Quantitative determination of chrysotile content was made by comparison of unknowns with calibrations of chrysolite dilution standards. The weight occurrence ranged from about 2-15%, with an average ranging from 3-6%. Lead compounds, quartz, calcite, mica, clays. barite, graphite, and alpha-iron particles were identified as well. ln sever<~! samples, weak, diffuse ref!ections suggested the presence of forsterite. but positive identification could not be made using this technique. Identification of ChryJotift hy Electron Microscopy Tran~mission electron micr?_s:opy, selected area electron_?J!.f~~ctioo, and elec- 1 .! >w.: a..:kno" kJ~.: th~ cuop~r:-~ti,,n of rh.: United 1\ut.,m<'hilc: Wc>rkc ~. L<'<:al Union ~o. 259 and the: Allll>mobik D.::.kr' lndu,ui;,l Rd;~ti<ns ;\"o.:iatin in h~lrin~ "' ,,tt:.in t!..:s.: ~-mrk~ in auw mairllcn.ln..:.: .;h,Jrs in th.: :-o;ew YurJ,. ar.:a. E:..:h samph: wa~ t"k.:n fnm"a typi.::.ljul.>" un<kr way at rh~ time. .i -- -. I .:I -:lj ,I I (.-j , L-.t,_ . i ! I I FMSI 06791 j I I I I I uJ: . w~. Ill, ,_,.Wrxt, -<' Zl w. ~~ Zl 0 IX 5z w -co: 0 t; g 0uz 0 u 5g 0u zw >- (.') 114 i) i .. - !- --- Ir - tron micr,1probe analysis of tht! brake dusts were carried out on each of the ten-- samples after preparation by a tcchniyue which di;;p<!rscs the uust particles in a -nitrocelluluse film without altering panicle:: size distribution. Free chrysotile fiher- bunules and fibril.s were observed in all ten samples (Fig. 1). Selected area elec- tron diffraction analysis of representative fibers demonstrated the preservation of the chrysotik !'itructure (Figs. 1A. B). Some patterns displayed arcuate reflections suggestivt! of interfibril rotation and intrafibril displacement (Figs. 2A, B). Occa- sionally, fibers were observed without characteristic chrysotile morphology. with mottled sutfaces and obliterated fibrils. indicating partial or complete recrystalli- Ization .. Electron . . . -diffraction patterns obtained fro-m--these-p-arti-c-le--s---disp-la-y-e-d- :z I<~ z0 ,tm3: I~~ ~'"~" :m }>- n:>:> :r: 0 :::> c.. 9 z nm. or0 FH;. I. Ek.::trllnpht>tornicngraph br~.: chr~ 'l'!ik tounJl~ in toral-t: Jrum Lith! t'S.Ot\0:< m:~gnifo.::t n0 .,() tion). Othn p.n1icle:; inclll<!'-' ph<:n<l r~,;n h.~J~r an,! ro.\J <hh! Jcbris. I0z n -lclli:YJ:IUII .0- 0 C-<l FMSI 06792 I- I .iHhVJ 115 F1c. 2. Sdecled area eleclron di!Trac1ion p;tllern5 obi;~ined on fiber:; of chry5otile obt:tined during ~i;: sampling at br:tke repair shops. In A. the reciprocal'' :t.xis is marked a as are the layer lines.in the (OK!) series. lmlexing of upp~r ri!;hl qu:~Jr:tnl )i..:IJcJ 16 n:fl.:ctiuns cvrrc\P.,nJing tu single crystal X-ra) Jinracrinn analysis of\Vhillakcr anJ Ztissman. 1956. Patlcrn in (B) displays "smearing of rellections in a "clockwise'" manna suggesting interplanar rotation. polycrystalline characteristics of multiple random reflections or Debye-Scherrer rings rather than the distinctive singk fiber chrysotik pattern (Fig. 28). Microchemical analysis \Vith a probe technique on the un:~ltered fibers showed them to possess the usual Mg:Si ratio of chrysotile. In addition to free chrysotile fiber bttndles 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 nil of them are shorter than 0.4 J.Lm in length; virtually all are of respirable size (-5 JLm). Hatch 0970) in reporting on . 9ptical fibt:r counts obtain~d from brakt: cleaning operations with compressed air jet, found that 94% of the fibers fell in the ~-5 JLm length category. while only 6% were longer than 5 pm. Jacko anJ DuCharme (1973) made size distribution mt:asurements of asbestos fibers in brake dusts generated during dynomom_eter tests. using both optical and electron microscopy. They fL'tmd. at m:1gnifi~:ations of 22.000x that 30% of the fibers were from 0.25 to0.50 /tm in length and that 60% were longer th~m 0.5 J.Lnl. Some dis~:repuncies between our dala ami those of Jacko and DuCharmt: may be attributed to th~ir u:o.c of the lower m;tgnifi~:atilHl (:::!2.000x vs 42.000x). at which fibers shlHter th<Hl 0..20 pm m:-ty nut be: c;tsily seen or identified on the electron micws~.opic screen. Thus, hlHh th~ optical fiber CLlllnt I .. - . .d:1ta in other stuuics and the clc.:tnm miLroscopic fiber siLc distributiLlll data i . '".-ir (ll' r.... ,, ., 1 ~--~---- FMSI 06793 I uxl, ~I IJl . ~I izl, ~. w5z1l "c0 D b 0_, u0z 0 u 'o6 : 0 u wz >- () -- ------------------- ------------------- 116 .I) ----'I-. I mz :S ;>o ! 0z I>z .~- F1c. 3. Electron photomicrographs of brake drum dusts. Chrysotile is present in both free fiber and fit-ril form. Opaque granular material is road dust or phenolic binder. a .. ><10,800; b. x9300: c. x}O,OOO; d. x30,000. .:.: ~ ,- I ::0 m indicate that the chrysolite fiber population generated by brake wear is a strongly 1./l m skewed one, with <llmost all fibers concentrated in the smaller than 5 p.m region. :> ;;o No attempt was made to size the asbestos-binder particulates. () :r: Personal Air Sampling during Brake Rtpair Wor/.; 0 :::> o_ P.::rsonal air sampling for asbestos e:\posurc during brake linin!! maintenance () and r.::pair wa<; carried out Cll franchi-;cJ auto dealer gar:tge-.. taxi t1cet repair z-< sh0po;, anJ a municipal truck rep::~ir shnp. alllt'Cat.:d in N--:w York City.) Per::-onal rnn I : 00 lA~~i"t~\:l~c in f'H''iding opportuuir> f,)r ~;~rnphng \'.~' bi"r.-n r~ th~ D.:p.~rtn1~nt t'f Air R\!..;.fun.::es. ' Cl ~c" Yok City. I(!n I z0 I . . . lF li'l>.l!l () ,0.... 0 Cl -< FMSI 06794 !Hr~'.l.l ! TABLE~ Lt"<:Tit Dt5ll<llll'TIO>; .... Clll<\"~01111 FIR>:!<''" OR.\J..t. D><L"'[ Dt'Sr" 117 Sample 750-1500..\ N (SC) 1500-2250A Nt%) nso-JOOOA N!~l JOO()- 3750..\ N(t;i-) Total I%) I 40 34 II II 96 2 32 23 32 87 3 20 25 25 70 4 26 37 26 7 96 5 57 11 4 78 I. 6 23 9 12 12 56 7 50 26 21 2 99 8 29 30 21 17 97 96 41 18 10 7.5 10 II 6 31 31 79 ~ Fib:~=~:~~d ~d--~~~:~:2::.~~~- ftbe: ~~:~~~=~:~~fr?m 250-to_s_oo_.l._._-----:-- air samples were taken during ami after brake repair work and at varying distar.1ces . from the work sites in other areas of the garages and shops. The latter samples were intended to provide information concerning levels of asbes,tos exposure which garage employees other than those doing brake work might experience. Asbestos Exposure during Automobile Brake RepCiir il'ork Air samples were first taken in the breathing zone of mechanics doing brake repair work. These peak exposure measurements were taken over periods of 3-8 minutes during which the workers were blowing dust from brake drums. The air samples. taken on membrane filters. were processed, ami fiber counts made in accordance with the procedures which have been adopted by the Occupational Safety and H~alth Administration (OSHA) of the U.S. Department of Labor (Bayer, Brown, and Zumwnlde. 1975). Essentially, the nnalysis consists of counting fibers 5 to 100 /-LID, in a fixed nrea of a Porton graticule. using phase contrast microscopy at a magnification of 400x. This microscopi;: 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 air jet. A recent survey of brake repair establishments in Baltimore and Washington revealed that this is the standard method in those cities C(:astleman 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 tt;"; operator's area under these condit!ons {an average concentration of 16 fibers/ml), and that there are significant concentrations at least 20 ft away. Background or area s3mpling during the same operation shows that. at least J..J minutes after jet air blowing and up to 75ft away. asbestos concentrations are still mc:asurahle even by optical microscopy. The data in Table 3 indicate that an ast-e.;;tos concentration gradient. dcp<.?mknt on distance and time. is a;;sociated with thi-; operation. It is eviJcnt th;1t any person 65-75 ft away can be e~pn.;ed. Current (interim) regula- urtions 0 S 1!.-\ prohibit concentrations of 5 llberstmt or Oltlre. l<'ng.:r than 5 Jtlll, a~ I I(- i (11'"r!:l'. .t: I I .I I I :uew<:xr:: wV) 0: ;..{.I. .z.... .. az~l 0: ~ w "'c0 0 0o__. : u0z 0 u (3 9 0uzw ~ FMSI 06795 118 [) \ f- I I ---I ( zm < ::0 0z ~ mz ~ r;:o m tn m > ' n;:o ~ 0 :J Q_ :z!C) i .., n g0 , n 0z n 0 0 C) -< F1c. -1. Rt!mov::.l of dust from br;,kc drum and back pbt~ b} pn~umatic air blowing at automobil~ garage. I a time-weighted average for workers. and concentrations above 2 fiberslml will be illegal after 1976. Regulations set a peak concentration (maximum excursion) of I0 fibers/ml of air. Newly proposed standards are designed to set a limit of 0.5 fibers/ml (500.000 fibers/m 3), with a maximum excursion of 5 fibersfml. It was generally found that there was minimal, if any, effort to control dust in most garages. Workmen do not use respiratory protection. There was little awareness of the potential hazard of brake dust. In a single instance, brake drum cleaning was not done with a compressed _air jet, but wi;l; a dry hand brush. Fiber concentrations were somewhat less (:?..5 fibers/ml) at the operator level. but background Je,els 12 ft away were the same as with air jet cleaning. Ashestos Exposure during Trttck Brake RepClir and Installation Work Person~1l air sampling was also conJucted at the f'ew York Department of S::mitation truck repair shop. where \ari011;; kint.ls of brake application and repair work are perfL>rmet.l. Used truck tJJ;tl,.:e linings arc- salv~g<'t.l by ,grinuing the surface to remove grea-;c and dirt. and n<:w !inin;;s arc ground tL) cxr..-dite break-in. Tht! edges of new lining-; arc bevcbJ on a ~rinding whc..:l 0r :m:ing machine to a\'oid n0i:,c problems. (Fig. 5). flok~ ;uc Jri!L.:d or punch;:t.l into the brake lining. \\hich 'i FMSI 06796 it I'I ,',[I 119 TAHLE J A~nr~ ros Co";r." rR.\ no:-.;s r>L.Ko"c: 1\L n>~Hllltl.t. BHAH Sr11ncr. 4 Fiber concenlr:uion Operation Distance (fl) Numhc:r of samples (liberslml! Range: Blowing dust ou1 of brake 3-.5 4 16.0 6.6-29.8 drums with compressed .5-10 3 3.3 2.0-4.2 air jet 10-20 2 2.6 0.4-4.8 Dislancc from op~ra1ion (fl) Time lapse (min) Concentration (fiberslml) Background samples token 10 0 0.3 at varying distance and lapsed times. aftc:r brake drum blowing 20 1:! 50 0 0.8 s 0.2 s 0.1 65 7 0.1 75 14 0.1 Distance Number of Fiber concentralion 1\\,bers/ml) sampks Mean Range Cleaning brake: Jrums wilh dry brush Background samples taken J minutes afrer cleaning br<~ke drums wilh dry bnt~h 1-J 12 2 2.5 1.3-3.6 3 0.1 0-0.2 a Fib.:rs 5-100 pm in length, counh:J by r>ptical microscopy. The new propused Ashesros Stambrd of rhe U. S. Depanment of Lnbur records a~besros exposure in fibersfm 1 noting thai a workon;,n mi1;ht rc'>pire approximatt:ly 8 m' of air ~r working tlay, rcrain- ing an unsrudic:J proportion of inhakd fibc:rs. The above tabI~ omits rdcrence to air content of fibers .,< .5 p.m in 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 tibers/ml was found in the breathing zone of the operator. The data show that measurable fiber concentrations are found 25 ft or more away. At a distance of 25 ft, for example, a concentration of I fiber/ml ( 1,000.000 fibas/mP) was found. Much larger numbers of shorter fibers woulJ simultaneously be inhakd. During the bl!vding of truck brake shoes on a grinding m;)chine, very high concentrations of fibers were found in the vicinity of the operator. The average of five air sampks was about 37 fibers/mi. Area samples, taken up hl 30ft away from this operation. demonstrated the presence of airborne fibers. It was of interest to note th:tt, at the time of this sampling, from eight to 15 other garage mech::wics wen: \\'Orkin~ within this t" -,-l', . - rr:;(_~,, I I uw:o<Xx: <wI) c..c..:. ~z w ~z 0ox >zw -uc 0 >e>- 0 u0z 0 u 5 0 0 u wz e>>- FMSI 06797 -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - _ _ _ _ _ _ _ _c.;.;::::.:..:.....;.c--"""'----''--'-'-'----'..:.:.:.:..:.c:l~ ,. \ 120,:\ I I i I ...I.. r I m F1c. 5. Beveling of truck brake linings at municipal garage. Arrow indicates accumubtion of asbesto~ ~ dust. :;o .- . -r 0z 3: perimeter and were exposed to asbestos. Fiber levels for other kinds cif operations z.m.... at the truck garage are given in Tuble 4. .>.- Boillat und Lob (1973) h:we repcrted fiber concentrations measured dui'ing :;o drilling holes for rivets and grinding. They found values ranging from 0.3 to 29.2 :m:;:; fibersiml: four of the nine values exceeded 5 fibers/mi. }> n:;o A Comparison of Fiher Lnels Visible by Light Microscopy wul Electron Micros:r: copy g 0. In the ten brake drum dust samples examined, it was found th:J.t asbt!stos fibers b shorter than 0.-1 ;.tm predominated (Table 2). The OSHA r\;;b~~tos Staml:trd does n7-<. not require: that short fibers (< 5 p.m in length) be c.nmteJ (>r controlkJ. This 0\ei.,i::ht may have COn<>iller;lhle hiok)gt.:al significance in that small chry~otile gQ fit-er~ rt:adily produce a~t>.:stc's clist::l'>e (1-loll. ~lilk ~tnd Youn!!. 196-1. 1965; D~1vi~. 1965; Pott, Huth, and Friedrichs. 1972; Wagn.:r, Derry and Timbrdl. 1973: ~ .IA lcor,~:l;tll I Slj ~~1-------------------------------------------------------~---- FMSI 06798 H~.\11 ! i!EXl _,_ ------ 121 . FIC:. 6. R.:newing of municipal tru.:k brake linings by light grimling to remoe greas~ and dir:t: Hilscher et al., 1970). Altention has recently been again called to the potential importance of this question (Bouhuys, 1975). There is little published information on the numbers of, and sizes of. submicro- toscopic asbestos fiber:; in occupJ.tional cxpusures. The present study afforded an opponunity collect data on the relationship between submicroscopically- and optically-visible libas for this specific industrial exposure. Eight air samples were sel~cted for both light and electron microscopic examination. Six of these were taken during bruke drum dust removal oper:llions with optical fiber counts recorded from 0.1 to 3.6 fibers.'ml. The other two samp!t:s were taken during light grinding of automobile brake shoes. Pnparation and Anll/.ni.\ of Air Snmples One square centimeh:r sections of the eight membr;mc filter::. were mounted, Ju~t sid~ dL)\':n, on micm~copic slides anli ash.::d in luw temperature activated :X: ~~ ~i tl) ~_i,, -=(! t- ~\ z~ 0 ~ UJ -co 0 b 0 u0z 0 u l5 9 0uzw b FMSI 06799 -1 l i I i l' ! I I I ; zrn ::5 ;;o :0zs: zm ~ r ;;o rn (., r.'l )> n;;o :I 0 :l Q_ C1 z-< .mg 5 () n 0z n .0-0 (I -< 122 ) i -J I TABLE -1 A soH~ ro~ Co,,-,_,.. 1 RYIIO-" OtRI"<: T~:n;~ BR.\H S[H\'Il:F. ft Distance Numt..:r of Fiber concentr;ttiun (fihers/ml) Operariun Rene" ing u~ed linings by srinJins Bacl.grounu to grinding used linings Be.ve!ing n~w linings Ba.:kground to b"veling new linings Punching rivets into brake linings Chipping rust off used br..tke linings Sweeping fluor around grinder Backgrouml to sweeping f1,1ur :J.round grinder (ft) sampl~' Mean R;:mge 3-5 10 3,8 1.7-7.0 10 ::! 1.5 1.2-1.7 :!5 2 0.8 0.6-1.0 60 I 0.:! 3-5 5 37.3 23.7-72.0 8 I 0.6 1:! 2 0.4 0.3-0.S 30 l 0.3 3-5 '2 1.5 1.9-2.0 3-5 2.4 3-5 3.6 ~ 15 3.1 Fibers 5-100 }Lm in length, counted by optical microscoov, oxygen to remove organic matcri:-tls. The ashed residue wus dispersed in a drop of nitroccllulus~ solution. The dispersal was accomplished by a .. rubout"' technique using the edge of a w:.~tch gbss (Nicholson, Rohl and Ferrand, 1971). By this method large asbestos fiber bundles are broken into their con'itituent smaller fibrils and large agglomerates of inorganic materials. which normally obscure the presence of asbestos fibers, are broken into particles small enough to allow virtually all asbestos to be seen. By placing a second sliue over the ground residue and njtrocel!ulose 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-coated electron microscopic grills. Typically, four grills are prepared from each sample anu one square on each grid is scanned in the electron microscope at 42,000x magnification to determine the quantity of chrysotile present. By estimating the length and diameter of each fiber, ami assuming a cyiindrical fiber geometry, tne 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 a'\bestos mass calculations obtained from the eight samples is shown in Table 5. Figure 9, showing the same tbta. is plott-.:d on logarithmic p:tper. and visual insp-:-ction inuic.ttt:s th~1t a positive corrdation ex.i-.t~ between the optical tnd el.:clron _micrlJ\copic r.:-;ults, nlthl1Ulh the data ar.: limitell ami th~ amount of__ . cur ,-~:,:.-f;; 1 FMSI 06800 t 1 { i I - lt-IEl\rJ --l,~c-:-~'_':'';~- --~: .... : .. ..,.. I ...... ...-~ ~ r. . '':- 123 I' I I I 1 I i I I I I I ~ i l .:.. . iI Ftc. 7. Electron photomi.:rog.raph of ;~ir sample taken during bmke drum blowing (~:.e ~a::-~ple No.4. Tab)e 5). Large numbers c7CI-100) of chrysotik. surne of which are rna~ked by gmnular p:trticulaces, presumably road dust (65.000 total m:>gnilicutionl. 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 coul~ be exposed to about 0.5 mg of asbestos daily in circumst::mces in \vhich the time-\veighted 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 mill inn fibers per cubic meter of air (of greatly varying diamt:!tcrs and lengths). extremely high concentrations of submicroscopic fibers are present up to 65ft 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! slanJ:~rJ optical coimting technique. The<;e limited data indicate that the standard (OSHA! optical fiber counting method m:1y be only a fractilHtal indicator of total asbestv:; expo- .lot:tlsure. at least in th.: ca~e of automobile rcp::tir work. They also imli.:ate that the e.xrosure is mt11.:h higher than the OSH.\ technique reconls. in terms of -~(oi;rri_.JII. -------- FMSI 06801 :r: ~ w wt l ) 0_:.: 3!<:(! ~ 0 ~I -~ w -co 0 (5 0 0 uz 0 u 5 0 0u "z-' >- l:) ,'-. )~4 I' I .. i -!I I -- -----. t . _..,-.iITI I... -= .I . ~--; : . -~ zm 0.5 fJ <::<; z0 ~ _:. ... I ..:~ 'mz Frc. 8. Electronmicrograph of air sample of cluster of chrysotile fibrils in b:lckcrour.d s<~rrt::t!e (see ,.,;;! r sa:n;::!~ No. 3, Tab!" 5 tll3,0..10x m:..gnificatio'!}. rn >Uml asbestos fiber number, mass, anJ surfilce area. Additional studies rele\'ant to this :n0 ami o:her kinds of asbestos exposure are ne~ded to confirm and extend lhest; :I: 0 finJings. It is important to note that p:micles of asbestos-containing pulverized "a.'.. brake lining were not incluJecl in this mass determination. Their importance, in C) terms of biologic potential. is presently unknO\vn. -z< nm SUMi,1ARY AND CONCLUSIONS 0 (I) Chrysntik asb.:sto~ ftba i<> a majur cornpunent of brake lining matcri:1l'\. 5 -C) ,-Dt:!;r~sLblion of . . -- ---- the - lining - .. is--l-:>.-mught . abo-u- t by a cumbin:ttion . of- -r~tc.tnr-s. -w-hich. n l0z n ICC)!" d~l-;t rr .0..... 0 (;) -< FMSI 06802 .I .. ----------- ------------- -------- ---------- I l TABLE 5 o ..Crni!'.~P.ISIIS Of ut:,\L A'Hl ELLCTRO" !\.locRncoolf" F1UFK Crlt::OO:I' 125 Operation I. Blowing du<;t off drum with air jet ( 10 fl away) 2. B"ckgroun.t to bh.l\ing out brak~ drum (10ft away) 3. Blowing dust off drum with air j~t C!O ft away) 4. B<JckgrounJ to blowing out llr.~ke drum CO fl ,.w,.y) j_ Background to blowing out brake drum (65 ft away-7 minutes aflr:r blowing stopped) 6. Cleaning brake drum with hand brush 7. -Light. grinJing'\ of new linings bcf,>re installation 8. Light grimlin:; r.ew lining; bdore installation Optical micro~cop)' (fib.:rshnll 2.0 0.3 0.4 0.8 .I ),(i 4.7 2.7 Electron mi.:roscopy (,u.g!m') 1.27 0.2 1.1 0.1 0.2 6.5 53.0 66.0 --T include thermal stress, m:.tterial fatigue, and shearing. Modifying agefltS are included in brake linings which lower the contact temperature between-the lining and wheel interface; this, in tum. prevents binder pyrolysis and chrysotile fiber de hydroxylation. The a'mount of c hrysotile fiber which survives the braking operation is related to a numher of additional factors, including so.me which are external to the properties anJ quality ofth.:: lining itself_ As a consequence, degradation may occur at t.::rnperatures signficantly lower than th:1t required for the dehydroxylation of chrysotile, with the persistence of fibers. (2) Ten samples of dust Wl!rc taken from automobile brake drums in New York City, and analyz~d. Optical microscopy was of limited usefulness. X-ray diffraction analysis, using bl1th continuous and step-scan modes demonstrated the presence of chrysotile in ::til dust s:1mples. The proportion of chrysotilc ranged from about 2-15%, and averaged about 3-6%. This included both Jrt;e.JibJ;J~S and chrysotile which survived in pulverized binder as particulates. Forsterite, the:_ J -..w~tn't=- .. COI'IRICIII 0 'l~ 0 0 0 0 0 o.L_.n______.__ -------- - ----------------- ~I .') tQ,J I.)OQ -- II - fMS\ 06803 I I I II:~X: < wl U) ~I ~I ~I g~zIl ~- I w -co 0 gb u0z 0 u l5 0 0 u wz b ,k_ I I ~6 ll I I I therm:tl transforn.latilln product of chrvsotilc could not be unequivocally id~ntified by continunus scan X-ray diffraction. (3) The presence of chrysotile asbestos in th.:: ten dust samples was further verified by transmission electron microscopy, selected area electron diffraction and electron microprobe analyses. Chrysotile was found. both in fiher ~,nd fibril form, with unaltered structure and chemical composition. Its frequency of occurrence wa~ consistent with: 'but lover .than the quantitative determin~tion' made by- X-ray dift"raction 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, partially altered and completely recrystallized fibers were also seen. (4) Size distribution analysis at 4:!.000x magnification in the ten samples indi- cate that about four-fifths of all chrysotile, in fiber form. is shorter than 0.4 J.lm in length. These fibers arc too small to be seen by optical microscopic techniques. I (5) Personal air sampling was conducted during brake repair work in automobile garages in New York City. Standard optical microscopic procedures for fiber I ! counting were used. In samplc:s taken in the vicinity of repairmen blo,ving dust from automobile brake drums with compressed air, an aver~ge~oncentration of 16 !1- fibers/ml was measured. Background and time-lapse samples imlicute that measurable concentrations exist at least 75 ft from. the work site and for at least 14 II minutes after jet air blowing. (6) Personal air samples were taken at a muniCipal truck repair facility where II I variuus brake fabrication and application operations are performed. Grinding of truck brake shoes resulted in an average concentration of about 4 fibers/ml {.:l,{XXl,()(){}'m 3). During beveling. an average fiber count of 37 fiberslml was 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 and application work. During light grinding of truck brake shoes, measurable fiba concentrations were found 25 ft or more zm ;<::; away. as \veil as up to 30 ft from brake beveling operations. The background measurements, during both automobile and truck brake work. indicate that many z0 3: employees in garages other than brake lining workers are potentially exposed to asbestos. including other mechanics and shop management. zm (7) Eight air samples taken during automobile brake repair work were analyzed .;t-:-;' 'X> by other optical and electron microscopy. A positive correlation was found to exist between optical fiber counts l > 5 J.lm) and the total chrysolite mass calcuia- m (/l m tions based on sizing all fibers ~1t 42,000x magnification. These data indicate that ~ :;u standard (OS 1-1 A) optical fiber counts may be a useful index of total free asbestos n :r exposure during brake repair work. They also demonstrate that the total free 0 - asbestos exposure. in terms of fiber number, mass, and surface area is much "a. greater ihan the opti.:al CL~unting techniques indicate. Cl z-< .mn 0 (8) Attention is called ICl the fa.:t that in addition to asbe-;tos, other biologically active substances. including free sili..:a and kaJ complHmds. have been id~ntificd in brake lining du"ts. Their concentrations in brake work environments arc not 0 knuwn, and warrant investigation. ICl n _j l 0nz -~U."lf'Jf:l-,i-:1 .0-- 0 Cl -< FMSI 06804 .\ 127 \ (9) Potentially hazardous asbestos expvsurc: exists tluring nt!tornotive brake servicing. It has been reported th::lt ~tpproximarcly 900.000 pasons are employt:d in such work in the United States. It is recommendeJ that stringent industrial hygiene measures to control exposure: be implemented as rapidly as possible. I ACKNOWLEDGMENT We thank Drs. A. E. Anderson. R. L. Gealer. and I. Eicht:n cii The Ford ~lotor Company for th~ir valuable comments in reviewing the manuscript. r REFERENCES 'Aml~rson, A. E. ( 19o9). Wear in brake materi.-.ts. Ill Proc .-\mN. Sue~ :\t,ltl!.\ Wcar C.mfnl'tiCt'. Anderson. A. E., Gealcr, R. L.. McCune. R. C .. :mJ Spr) s. J. \V. ( 19731. A.<h!'.IIIIS ~missimu from bra/..e dynamamerer lt'srs. Soc: Au10 '::ngin. Meeting. D.:troit. Michigan, 1+-IS May. 1973. Paper No. 730549. Bark, L. 5., l'.lomn. D. and Percival. S. 1. ( 1975). Chemical changes in asl:>estos-ba~ed friction materials during performance-a review. 1\'n~r 34. 131-139. Bate5. T. F. and Comer, J. J. ( 1957)./n Proc. 6th Nat" I Conf. Clays and Clay 1\liner::tlo~y. Tnt. Monog. Sec. 6, 237-~48. Bayer, S. G . Brown, T. A . nnd ZumwalJe. R. D. (1975). Document TRB4, l,;.S. Depnrtmt:nt or Health. Education and Welfare. Public Health Service. National lnsitut<! for Occupalion::.l Safety and Health. Cincinnati. Ohio. Berry. E. E. ( 1971 )_ Tht'fmnl <llltJiysis of nuiou.f chQ'sMile.! rtsing emled ,.-r.zt'r trnui.Hjs rcclmi<JIIt'S. In Proc. 2nd lnll Conf. PhysicaiChen.ical A~be5I05 Minerals. Louvain Uni,. 6-9 September, 1971. paper :!:7 15 pp. Boillat. M.A .. and Lob. M. ( 1973). Risk or a~be\losi~ in workers empl<)yed in re~lacing automobil.e brake lining~. Schwei~eriuhc Medd~tischt Wocht'flsdrriji 103, (39). D~+-1359. Bouhuys. A. ( 1975). Fiher~ and fioro~is. An11. lnzern. ,\f,d. 83(>). 898-1\99. Brindley. G. W .. and Hayami, R. !1%5). Mechanism of rormati>n or ronterite and enstatite from serpentint:. Min. Maf:. 35, IR9-195. Bur,,.:JJ. J. T. ( 1957). Sur.,.ey or pvs~ihl.: m.:~hani,m\. ll'o1>r, I, 119-141. Carroll. \V. G. (196:!). The manura~tUr<' or omke lining,. Bri/. Plnsrics AUJ;ll\1. .1J.J.-417. Ca5tlcman, B .. Camarota. L. A., Frit>ch. A. J .. l\lazzu~chi. S., and Cra'"~y. R. G. (1975). The haz:uds <)f a;!->,:,tos ft)r brake m~chaaics. Public H~a!zh R.p. 90 CNo. )I ~5+-256. Daykin, C. W. ( 1971). A sllld.' of rhc infrared JPI'Clrn of chrysotile cmd rc-lntoJ nritc'l(:/s. In Proc. 2nd Inti. Conf. Physicai-Ch~mical Ash~stos Minerals, Louvilin Univ. 6-9 S~p:~mb~r. 1971, p~~r No. ::!:6, 7 pp. Davis. J. M. J_ (1965). Electron-microscope: studies of asbestosis in m.-.n and animals. Ann. N. r. ,AcaJ. Sci. 13::!, 98-111. Harries. P. G. ( 1968). Asbestos h:tzan.l; in naval shipyard;. Ann. Occup. flyg. 11, 135-145. Harris. A. M. ( 1971). Thl! ef!tcu nf gri11ding on tilt stmcrural ard rlu:rmul pmpnries uf clrryso>tilt nsbesrusji!nrs. In Proc. 2nd Inti. Conr. Physical-Chemical AsbeMos :\.linerals. Lou\ain Univ. t'>-9 -September, 1971. Paper No. 3:::!A, 6 pp. Hatch. D. (1970). Possiblt: .alternalives to asbc=stos as a frictio~ material. 4nn. Occ11p. Hyg.' 13, 25-29. . - .. .- -- . - Hicki~h. D. E .. and Kni1;ht, K. L. (1970). Exposure: to abcstos during br~ke r.1aintenance. Ann. Occup. lin:. 13, 17-:! I. Hilschc:r, W., Sethi, S., Fric:drich>. K. H.. ::tnd Poll, F. (IIJ71l). Zus:~mm.:nh;m;;e Z"i~~hen Asbeslose and Fa~~r1flnge. Natnr,is_,.,.,_,choftt.'n 57, 356. Holt, P. F.. Milh. J .. anJ Young. D: K. ( 196-11. The early dT~cts of chrysotik asb~stc'S Jus on the rat lung.}. Patlr. Baa. 87, 15-::!3. Holt. P. F.. Mill\. J.. and Young. D. K. ( 19>5). E.,r<::rimt:ntal a~b~stos with f,:tr types of fil:-ers:- lmp.>nan::e ,,f sm:dl fibcrs. rl1111. S. r. Acad. Sci. .~:!. S7-97. Jad.o. :\1. G .. 01nd DuC'h:ume. R. T. r 1\lnl. Rt;oke cmi--:,n.;: Emi\,it>n m..:.t,ur.:m,:r.t; frc>m lrak.:- ami clutch linin!:' fr,Hn ~ch:ck,l mhik -;our-~l'i. EP,.\ R~f"'rt. 6!lll-IOil~O. I - u,r..-i!:.Jfl 1 :ur w<""' t3 ex ~z w z~ 0co= ~ UJ "c0 0 gb .u0oz u 6 0 0 u zLU >- ~ FMSI 06805 zm< :0 z0 3: mz ~ r- ;o m l/1 m > ;o (') :X 0 ~ CL Cl '-z< mn 0 0 nCl 0z n .0... 0 C) -< --Langer ..-\. \,\.. :lfld P<o1cy. F. n. 1197 3). 1dcntifi.:ation of ~ingk a,l:>e~tos fibers in human ti,ues. l11 of Fli,>!,;;i.::~1 Effect' of r\sbesto\ II'. [l,,g,w~ki. tr a/. Eds.)pp. 19-~5. l.r\.P..C. Lyon. France. L:~ns<r . .-\. '.I.. ~lacldcr. A- 0 .. and P<olcy. F. D. !1973). El<=ctron mi~w,.:upi.:a1 investigation of a~hc,:.>~ libas. Emir. llctdrh Pa.1p. 9. 63--80. L~ n~h. J. R. ( 196Sl. Br:~kc lining d.:.:omp<"ition prollucts.J. Air Ptllutinn Comrol Anoc. IS,ll24-8:!6. f'.kConndl. J.D. C. (1967)_ Elc<.:trnn micrll~copy and electron Jinr;lctiun. In "Physic;)! ~lethods in Determinative Mincr:tl,>gy" (J. Zu~sman. Ed.). pp. 3J5-370. Academic Press. New York. Man inez. E. ( 19titi). Chrysotik a'he,;tos: Rclation~hip of the surface ami thermal properties to th<: cry~t:Jl stru;:ture. CmwJtl Mining nnd ,\lt-I<J/1. Bull_ 69, -11-l-CO. Mon~rn:Jn. L J. ( 1971). Some ch.:mi.:a1 anJ mineralogi.:al aspects of the acid decompo>ition of chr: '''tile_ In Proc_ ~nd Inti. Cor; f. Physicai-Chemi..:al Ashesto~ f'.linerals. Louvain Univ. 6-9 September. 1971. paper No. 3;2. 9 pp. Naumann. A. W., and Dresha. W. H. ( 1':166). Th.: innuenc<: of sample texture on chry~otile dehydration. Amn. Minanl. 51, 1200-1~11. Nev. house. ~1. L. ( 1965). Epidemiology of mesc>thelial tumors in the London area. Awr. N. Y. A cad. Sci. 13 2, 579-Qil~. Nicholson. W. J .. R<>hl. A. N .. and Ferrand. E. F. (1971). Air pollution in Ne\~ York City. In 'Pro.:eedings of the Second International Clean Air Congress. (H. M. Englund and W. T. Berry. Ed~.). pp. 136-139. Academic Press. !';ew Yt>rk_ Poll. F .. Huth. F., and Friedrichs. K. H. (197~1- Tumors of rats 01fter i.p. iqjection of powdered chrysotile 01nd henz[a)pyrene. Zbl. Bakt. I. .-\bt. Orig. 155. 4f>3. Selikoff. I. J - Chmg, J .. and H:tmmoml. E. C. (19M). Asl:>estos exposure and r.eopla.sia. JA.\!A 188, 2~-~3. Selik<>ff. I. J.. Hammond. E_ C .. and Churg, J. (1968). Asb:!stos e"\posure. smt,king and neoplasia. JA.\IA 2fH,(2). 106-ll:!_ SelikoiT. l. J_, Nicholson. W. J .. and Langer, A. M. (1972). Asbestos air pollution. Arch. Emir. Hct:/:IJ. 25, 1-U. \Vagner. J_ C.. B.:rry, G .. and Timbrdl. V_ (197)). 1\le~othelilm;lla in rats ?..fter inoculation with a'he<tos and other m:~t.:rials. Brit. J. Cnnar 28. 173_ \Vhitt;!!-.t:r. E_ J. \\'., and Z'"'man, J. 19~6. Th~ ch:tr:lctcril_::ttion of serpentine mineral' by x-ray di!Tr:Ktion. Min. Mag. 31. 107. I i .i I II II II I I I I I- I I FMSI 06806