Document wqwkRqRNLzJGqqM2bMMd9n7Mo

MOUNT SINAI SCHOOL OF MEDICIN oj The City University ojNew York riri H AvtNur and iooth striet- nNliVv'^^OoRr* Tkturrimntcj Community Xltdicine ^ /./March 23, 1976 Dr. Erwin Eichen lord Motor Company Doom 162 6 The American Road Dearborn, Michigan 48123 Dear Dr. Eichen: 3 am enclosing a manuscript of "Asbestos exposure during brake lining maintenance and repair", which is being submitted for publication in Environmental Research. We would appreciate your comments, criticisms or suggestions. ANP.t si Enc. Arthur N. Rohl, Ph.D Environmental Sciences Laboratory 8005 1866 PRODUCED BY FORD ABSTRACT Date obtained on asbestoB exposure of garage mechanics during brake lining maintenance and repair work show that fiber con centrations frequently in excess of regulated limits, are common. The presence of chrysotile, ranging from 2 to 15 percent, in brake drum dusts, vbb demonstrated by x-ray diffraction, transmission electron microscopy, selected area electron diffraction and electron microprobe analyses. Unaltered chrysotile was found, both in fiber and fibril form, in air and brake drum dust samples. The chrysotile asbestos content of personal air samples, taken during automobile brake repair work, was measured both by optical and electron microscopic techniques. While a positive correlation exists between the types of measurements, the present technique of optically counting asbestos fibers may considerably under estimate the levels of total asbestos exposure. 8005 1867 PRODUCED BY FORD I Asbestos Exposure During Brake Lining Maintenance end Repair* Arthur N. Rohl, Arthur M. Langer, Wary S. Wolff and Irving Weisnan Environmental Sciences Laboratory Mount Sinai School of Medicine of the City University of New York New York, New York 10029 Introduction Imring the past decade, significant disease risk has been found associated with the inhalation of asbestos fibers in a number of occupational and environmental circumstances other than in asbestos mining, milling and manufacturing, where serious hazard was already known (Wagner et al., 1960; Newhouse and Thompson, 1965; Selikoff et al., 1964, 1965; Harries, 1968). Such exposures were found in the construction industry and in shipbuilding, 8S well as in other industrial settings where asbestos products were used. More recently, asbestos exposure has been suggested to occur during auto motive brake lining repair and installation work, and measurable concen trations of asbestos fiber were observed in the work environment of work men involved in these operations (Hickish and Knight, 1970; Batch, 1970; Boillat and Lob, 1973). With limited data available, however, uncertainty remained regarding the type and extent of asbestos exposure during this work. Some investigators have questioned whether free asbestos fibers survive the high temperatures produced during braking action (Lynch, 1968; * This research was supported by Center Grant ES 00928 of the National Institute of Environmental Health Sciences of the U.S. Department of Health, Education and Welfare. Assistance was also provided in part by the Health Research Council of the City of New York K?.C U 2329 and by the Lord Motor Company. 8005 1868 PRODUCED BY FORD L Hicklsh and Knight, 1970; Hatch, 1970) contending that asbestos decomposes bs 8 result of the high point contact temperatures produced at the inter face of the brake drum or disc and brake lining. We have sought to obtain information concerning asbestos exposure oi work men engaged in brake lining maintenance and brake shoe installation, by analysis Of residual dusts recovered from brake linings and by direct measurement of the free asbestos fiber content of workroom air in areas Where these operations take place. In the United States, an estimated Work force of at least 900,000 auto mechanics and garage workers are 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 jDuCharme, 1973), to add more to the burden Of asbestos air pollution (Selikoff, liicholson and Langer, 1972). Asbestos in friction materials 1 the United States, an estimated 11S 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 clutch friction materials amounts to 4.5 million pounds annually. Major constituents of brake linings A number of materials are commonly used in the manufacture of the three major automotive brake lining components (binder, fiber reinforcer, and property modifier). These are listed in Table l. 8005 1869 PRODUCED BY FORr Binder: Jn. ~~ -f - The birders used in tKe'automotive industry today are pri marily (phenolic resins^ vMch are noted for high binding efficiency and ability to withstand pyrolytic breakdown. Other materials have been used, in varying proportions, in addition to resins, for binder improvement (Table I). Fiber: For fiber reinforcement of the friction product, chrysotile asbestos is used almost exclusively. The mineral typically comprises from 40% to 50% of the brake product. Tiber grades 4 through 7 are used, and occasionally, several sizes are ad mixed or even calcined to improve'strengtheningicaaracter- is tics. , "t XJr* Modifiere: Perhaps the widest range of materials used in friction products are the property modifiers."'Nineteen^ representative compounds are listed in Table I. Modifiers are used for a timber of purposes; they are included to increase brake shoe ''density/' making the brake surface able to withstand high pressures (e.g., barite); they are included as "lubricants'* to reduce the coefficient of friction along the brake surface, and thereby prevent "grabbing" (e.g., lead compounds); they act as "friction agents" increasing the coefficient of friction and enhancing the braking action of the shoe (e.g., brass chips); they act as internal "abrasives," which help to "recondition" the braking surface and remove deposited de composition products (e.g., rottenstone, quartz); they act as "heat sinks," reducing binder pyrolysis and fiber de composition thereby extending the useful life of the lining (e.g., brass chips, metals, etc.). 8005 1870 fZQ PRODUCED BY FORD I1 It is Important to note that one major purpose of the reconditioning agents la to retard the formation of forsterite (a mineral not originally present in the brake material, but created by dehydroxylntion and re- crystallisation of chrysotile asbestos at high temperatures) which may y y y' accumulate on the surface of the brake lining. The hardness of the forsterite (Mohs, 6.5-7.0) is such that it tends to score and gouge brake XV-' `^(^linings (hardncs^yJt-3^5)), degrading them prematurely. Therefore, re- Vi v crystallisation of chrysotile to forsterite is an unwanted effect, V jf O' hindered insofar as possible by the modifiers present in the matrix. 'X- 0-\ - Materials of biological interest Asbestos, quart?., and heavy metals are constituents of automotive brake linings, each warranting special consideration from the viewpoint of biological activity. The focus of this report is limited to the problem of chrysotile asbestos exposure. Mechanisms of degradation of brake linings during use brake wear is dependent upon many factors, such as the temperature gener ated at the surface of the brake shoe during braking operations. At any one time, only a small percentage of the rubbing area is in contact with the wheel, with "hot spots" generated, ranging up to 800 to l,000c (Carroll, 1962; Anderson, 1969). It is not uncommon during moderate ---- --------------- -----// braking action, to attain temperatures as high as (&00 C (Anderson, 1969).)^. ' ..-^C S ------------------------------------------, vb "' Some investigators have suggested that, in addition to binder pyrolysis, ^l! chrysotile completely dehydroxylates under these conditions and "reduces to powder" where it is swept off the brake facing (Carroll, 1962). How ever, this hypothesis is oversimplified, in that other important pro cesses, besides thermal wear, contribute to shoe breakdown, and brake shoe degradation. PQ8005 1871 PRODUCED BY FORD vS* (Durwell, 1957). For example, the effects of abrasive wear and macro- shear 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 (Muzutani ct al., 1973). This shear strain produces material fatigue which, with binder pyrolysis, can cause brake lining disintegration at temperatures far below those required for chrysotile dehydroxylation. Therefore, brake lining disintegration may liberate partially altered, or unaltered, chrysotile fibers. Thermo3 decomposition of chrysotile Differential thermal analysis indicates that chrysotile undergoes dehydroxyl ati on at 650C to 680C and recrystallizes (anhydrous magnesium silicate to forsterite) (Mg^SiO^) at about B10C to 820C (e.g., Martinez, 1966; Daykin, 1971; Berry, 1971; Montanan, 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, for sterite has been noted to form, during prolonged static heating, at con siderably lower temperatures (Bates and Comer, 1957; Martinez., 1966; Brindley and Hayami, 1965; Naumann and Dresher, 1966). In general, temperatures in excess of 570C are required for dehydroxylation and in cipient 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. 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 8005 1872 PRODUCED BY FORD -G- end scanning electron microscopy with microchemical capability, lor the purpose o determining the presence or absence of chrysotile. Optical microscopy, employing polarized light, was generally not useful lor detecting asbestos in brake drum dust. A number of factors are con sidered responsible lor this phenomenon including the low relief and bire fringence of chrysotile and the nature of the matrix, consisting largely of road dust, resin binder and pyrolyzed residue, which, in optical micro scopic preparations, readily obscures the smaller asbestos fibers. X-ray diffractometry, in the continuous and step-scan mode, was performed on ail dusts. Chrysotile reflections (hkl = 002; 020; 004) were observed in all ten samples. The weight occurrence ranged frcn about 2-15 percent, with ar; average ranging from 3-6 percent.-- Lead'phases, quartz, calci'te, idea, clays, barite, graphite and alpha-iron particles 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 chrysotile by electron microscopy Transmission electron microscopy, selected area electron diffraction and electron microprobe analysis of the brake dusts were carried out on each of the ten samples after preparation by a technique which disperses the dust particles in a nitrocellulose film without altering particle size* * We acknowledge the cooperation of the United Automobile Workers, Local Union -259 and the Automobile Dealers Industrial Relations Association in helping us obtain these samples in auto maintenance shops 5n the New York area. Each sample was taken from "a typical job" under way at the time. PRODUCED BY FORD 8005 1873 distribution. Free chrysotile liber bundles and fibrils vere observed in ell ten samples (Fig. 1). Selected area electron diffraction analysis of representative fibers demonstrated the preservation of the Cbrysotile structure (Figs. 2A L B). Some patterns displayed arcuate reflections suggestive of interfibril rotation and intra/ibril displace ment (Figs. 2A & B). Occasionally, fibers were observed without charac teristic chrysotile morphology, with mottled surfaces and obliterated fibrils, indicating partial or complete recrystallization. Electron diffraction patterns obtained from these particles displayed polycrystal-- line characteristics of multiple random reflections or Debye-Scherrer rings rather than the distinctive single fiber chrysotile pattern (Fig. 2B). Microcbenacal analysis with a probe technique on the unaltered fibers showed them to possess the usual Mg:Si ratio of chrysotile (Fig. 3). In addition to free chrysotile fiber bundles, and fibrils, chrysotile'was also frequently observed projecting from the margins of binder fragments Free asbestos fibers present in the decomposed lining dusts were sized at 42,000X magnification. The results, seen in Table 11, show that most fibers are too small to be seen by optical microscopy; almost all of them are shorter than 0.4pm in length; virtually all are of respirable size. Hatch (1970) in reporting on optical fiber counts obtained from brake cleaning operations with compressed air jet, found that 94fc of the fibers fell in the 2-5pm length category, while only 6% were longer than 5pic. Jacko and BuCharae (1973) made size distribution measurements of asbestos fibers in brake dusts generated during dyna mometer tests, using both optical and electron microscopy. They found, at magnifications of 22.000X, that 30n of the fibers vere from 0.25jr to O.SOpru in length and that 60S were longer than 0.50pm. Sore dis crepancies between our data arid those of Jacko and DuCharme may he 8005 1874 PRODUCED BY FORD attributed tc their use of a lower magnification (22,0005 vs. 42,000X)f at which fibers shorter than 0.20pn> cay 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 indicate that the chrysotile fiber population generated by brake wear is a strongly skewed one, with almost all fibers concentrated in the smaller than opm region. No attempt was made to size the asbestos-binder particulates. Personal air sampling during brake repair work Personal air sampling for asbestos exposure during brake lining maintenance and repair was carried out at franchised auto dealer garages, taxi fleet repair shops and a municipal truck repair shop, all located in New York * City. Personal air samples were taken during_and.after brake repair work and at varying distances from the work sites in other areas of the garages and shops. The latter samples were intended to provide information concerning levels of asbestos exposure which garage employees other than those doing brake work might experience. Asbestos exposure during automobile brake repair work Air samples were first taken in the breathing zone of mechanics doing brake repair work. These peak exposure measurements were taken over periods of 3-8 minutes during which the workers were blowing dust from brake drums. * Assistance in providing opportunity for sampling was given by the Department o: Air Resources, New York City. 8005 1875 PRODUCED BY FORD The air samples, taken on membrane filters, were processed, and fiber counts made in accordance with the procedures which have been adopted by rw the Occupational Safety and Health Administration (0SEA) of the U.S. Department of Labor (Bayer, Brown and Zunwalde, 1575). Essentially, the analysis consists of counting fibers 5pm to 100pm, in a fixed area of a Porton graticule, using phase contrast microscopy at a nagnificaticn of 400X. This microscopic method enhances image contrast and allows large asbestos fibers to be readily seen and counted. Sj-vr'A^O 0 ,1 > J ~ .\4 /(rJ b ' 7 / J . ^ i , 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 end Washington revealed that this is the standard method in those cities (Castlcman et al, , 1575). A similar situation exists in New.York City. The cloud of dust ___ that is produced is visible for several minutes af terv e-ds VCTi g . <). \ Table 111 shows that fiber concentrations are high in the operator's r` : rS area under these conditions (an average concentration of 15 fibers/ml), i ''O ; \ '> hV , ft ' *Vf'; V and that there are significant concentrations at least 20 feet away. ..............- .........._ .............. -........... -- . ________________ . /Background or area sampling during the same operation shows that, at | J least 14 minutes after jet air blowing and up to 75 feet away, asbestos \ .. "^concentrations are still measurable even by optical microscopy. The data in Table 111 indicate that an asbestos concentration gradient, dependent on distance and time, is associated with this operation. It is evident that any person 65-75 feet away can be exposed. Current (interim) regu lations of OSRA prohibit concentrations of 5 fibers/ml or more, longer than 5pm, as a time-weighted average for workers, and concentrations above 2 fibers/ml will be illegal after 1976. Regulations set a peak 8005 1876 PRODUCED BY FORD -30- concentration (maximum excursion) of 10 fibers/ml of air. Xewly proposed standards are designed to set a limit of 0.5 fibers/rl (500,000 fibers/m3 ), with a maximum excursion of 5 fibers/ml. It was generally found that there was minimal, if any, effort to control dust in most garages. Workmen do not use respirator- 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 with a dry hand brush. Fiber concentra-rtons were somewhat less (2.5 fibers/ml) at the operator, but background levels 12 feet away were the same 8s with air jet cleaning. Asbestos exposure during truck brake repair and installation work (!/ ;. ,K. i i Personal air sampling vas also conducted at the New Fork Departmen of, < /-'.'ill' Sanitation truck repair shop, where various kinds of crake application s'" ' " -----------------------------------* and repair work are performed. A ^large proportion of used truck brake ~ ---------------4^. Ljy-C''[}, linings.are salvaged by grinding the surface to remora grease and in-J> ^ N perfections on the surfaces, and the edges of new linings are beveled on') a grinding wheel or arcing machine so that the brake rill grip pronerly \ (Fig. 5). Holes are drilled or punched into the brake lining, which is -js-ri-Ti ~j' Ck'--J then riveted onto a steel plate. Some of these operations are similar Xc to those done during the manufacture of brake shoes. Table IV summarizes , the results of personal air sampling in the course o: this work. During light grinding of truck brake shoes (Fig. 6), an average peak concentra tion of about 4 fibers.'nl was found in the breathing core of the operator. The data show that measurable fiber concentrations ana found 25 feet or more away. At a distance of 25 feet, for example, a concentration of 8005 1877 PRODUCED BY FORD 11 3 1 fiber/ml (1,000,000 fibers/m ) was found. Much larger numbers of shorter fibers would simultaneously be inhaled. During the beveling of truck brake shoes on a grinding machine, very high concentrations of fibers were found in the vicinity of the operator. The average of five air samples was about 37 iibers/ml. Area samples, taken up to 30 feet away from this operation, demonstrated the presence of airborne fibers. It was of interest to note that, at the time of this sampling, from 8-15 other garage mechanics were working within this perimeter and were exposed to asbestos. Fiber levels for other kinds of operations at the truck garage are given in Table IV. Boillat and Lob (1973) have reported fiber concentrations measured during punchingjholes for rivets and grinding. They found values ranging from 0.3 to 29.2 fibers/ml; four of the nine values exceeded 5 iibers/ml. A comparison of fiber levels visible by light microscopy and electron microscopy In the ten brake drum dust samples examined, it was found that asbestos fibers shorter than 0.4pr predominated (Table 11). The OSKA Asbestos Standard does not require that short fibers (< 5pm in length) be counted or controlled. This oversight may have considerable biological signifi cance in that small chrysotile fibers readily produce asbestos disease (Bolt, Mills, and Young, 1964, 1965; Davis, 1965; Fott, Buth, and Friedrichs, 1972; Wagner, Berry and Timbrell, 1973; Hilscber et al., 1970). Attention 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, subnicroscopic asbestos fibers in occupational exposures. The present PRODUCED BY FORD 8005 1878 study afforded an opportunity to collect data on the relationship between 9ubmicroseopically~ and optically-vlsible fibers for this specific in dustrial 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 fiber counts recorded from 0.1 to 3.6 fibers/ml. 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 temperature acti vated oxygen to remove organic materials. The ashed residue was dispersed in a drop of nitrocellulose solution. The dispersal vas accomplished by a ''rubout" technique using the edge of a watchglass (Nicholson, Kohl and Perrand, 1973). By this 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, are broken into particles small enough to allow virtually all asbestos to be seen. By placing a second slide over the ground residue and nitro cellulose solution and then gliding the two slides apart, a thin film is produced. The dried film is cut into segments which are then floated off in water. The film is mounted onto Formvar-coated electron micro scopic grids. Typically, four grids are prepared from each sample and one square on each grid is scanned in the electron microscope at 42,000X magnification to determine .the quantity of chrysotile present. By esti mating the length and diameter of each fiber, and assuming a cylindrical fiber geometry, the mass of chrysotile per grid square is determined. Representative electron photomicrographs of chrysotile fibers and fibrils 8005 1879 PRODUCED BY FORD ere shown in Figs. 7 and 8. O' ( C /. "A ~/.t\>J': ."' *J. c( Results J& ^uU Js ttp, -C-.^.-f' ^5 C;J.a * j.Jix, , 1 `-''-Z- 'S'J.j t<{"'"d /.iZj . A comparison oi the optical microscopic fiber counts and the electron .- / d-O^j^ fyy microscopic total asbestos mass calculations obtained from the eight :!/u` f' ' ~i' samples is shown in^Table V. Figure 9,)showing the same data, is plotted-'-?"-^ on logarithmic paper, and visual inspection indicates that a positive correlation exists between the optical and electron microscopic results. For example, from these data it may be possible to predict that, during the grinding of new brake linings, a worker could be exposed to about 0.5^g)per cubic meter of asbestos daily in circumstances in which the time-weighted TLV of 5 fibers/ml would not have been exceeded. Similarly, Figure 9 shows that, since a microgram of asbestos represents on the order of one million fibers per cubic meter of air (of greatly varying diameters and lengths), extremely high concentrations of subaicroscopic fibers are present up to 65 feet away from brake repair work (e.g., sample No. 5), even'though fiber levels in such a case are barely de tected, if at all, by the standard optical counting technique. These limited data indicate that the standard (OSKA) optical fiber counting method may be a useful index of total asbestos exposure, at least in the case of automobile repair work. They also indicate that the total ex posure is ouch higher than the OSKA technique records, in terms of as bestos fiber number, mass and 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 particles of asbestos- containing pulverized brake' lining were not included in this mass deter- VO o o VF oo VO O ^"^5 c initiation. Their importance, in terms of biologic potential, as presently unknown. <\ . cf 4 4t: ^ rl ' J *-! / / .o~ -Ud+Aji^ suJ-5; e, n> ~ f-m , ^ .f, < /.eiWvvl0i . . qc. c 'OTP'.'; r-f r.lj. d . - ' i ' c JU r^d\, .V,.v .d ,..........."* v - ^ ' PRODUCED BY FORD Summary and Conclusions 1. Chrysotile asbestos fiber is a major component of brake lining materials. Degradation of the lining is brought about by a combina tion of factors, which include thermal stress, material fatigue and shearing. Modifying agents are included in brake linings which lower the contact temperature between the lining and wheel interface; this, in turn, prevents binder pyrolysis and chrysotile fiber dehydroxylation. The amount of chrysotile fiber which survives the braking operation is related to a number of additional factors, including some which are external to the properties and quality of the lining itself. As a consequence, degradation may occur at temperatures significantly lower than that required for the defcydroxylation of chrysotile, with the persistence of fibers. 2. Ten samples of dust were taker, from automobile brake drums in Xev Tori: City, and analyzed. Optical microscop}- was of limited use fulness. X-ray diffraction analysis, using both continuous and stepscan modes demonstrated the presence of chrysotile in all dust samples. The proportion of chrysotile ranged from about 2-15 percent, and averaged about 3-6 percent. This included both free fibers and chrysotile which survived in pulverized binder as particulates. Forsterite, the thermal transformation product of chrysotile could not be 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 microprobe analyses. Chrysotile as found, both in fiber and fibril form, with unaltered structure 8005 1881 PRODUCED BY FORD and chemical composition. Its frequency.of occurrence was consistent with, but lower than the quantitative determination made by x-ray diffraction analysis. However, it should be noted that x-ray diffrac tion 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 42.000X magnification in the ten samples indicate that about four-fifths of all chrysotile, in fiber form, is shorter than 0.4pm in length. These fibers are too small to be seen by optical microscopic techniques. 5. Personal air sampling was conducted during brake repair work in auto mobile garages in Nev York City. Standard optical microscopic pro cedures for fiber counting were used. In samples taken in the vicin ity of repairmen blowing dust from automobile brake drums with com pressed air, an average concentration of 16 fibers/ml was measured. Background 8nd time-lapse samples indicate that measurable concentra tions exist at least 75 feet from the work site and for at least 14 minutes after jet air blowing. 6. Personal air samples were taken at a municipal truck repair facility where various brake fabrication and application operations are per form'd. Grinding of truck brake shoes resulted in an average con- 3 ccritration of about 4 fibers/ml (4,000,000/n ). Burning beveling, an average fiber count of 37 fibers/ml was measured. Exposure levels during drilling, punching rivets and cleanup were also measured. 8005 1882 PRODUCED BY FORD Background measurements show that fiber concentration gradients are produced during truck brake repair and application work. During light grinding of truck brake shoes, measurable fiber concentrations were found 25 feet or more away, as well as up to 30 feet from brake beveling operations. The background measurements, during both auto mobile 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. Eight air samples taken during automobile brake repair work were analyzed by both optical and electron microscopy. A positive corre lation was found to exist between optical fiber counts (> 5jjm) and the total chrysotile mass calculations based on sizing all fibers at 42,000X magnification. These data indicate that standard (OSM) 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 and surface area is much greater than the optical counting techniques indicate. 8. Attention is called to the fact that in addition to asbestos, other biologically active substances, including free silica and lead com pounds, have been identified in brake lining dusts. Their concentra tions in brake work environments are not kr.o~.Ti,. and warrant investi gation. 9. Potentially hazardous asbestos exposure exists during automotive brake servicing. It has been reported that approximately 900,000 persons arc employed in such work in the United States. It is 8005 1883 PRODUCED BY FORD recommended that stringent industrial hygiene measures to control exposure be implemented as rapidly as possible. 8005 1884 PRODUCED BY FORD References Anderson, A.E._ (19B9)^_Wear in brake materials. c^m. Wear Conf. Inj/Proc. Amer.. SeCj.y' ,n<' W" , fn* jU-'jP' a--'' T . . S/ Anderson, A.E., Gealer7 L., McCune, R.C. and Sprys, J.W. (1973). Asbestos emissions from brake dynamometer tests. BAfcC Soc. Auto. Engin. Meeting, Detroit, Michigan 14-18 May, 1973, (Rpi,> 730549. ' A Pa.^v *yJT. Ball, M.C., Taylor, H.F.W. (1963). The dehydration of chrysotile in air and under hydrothermal conditions. Min. Mag., 35, 467-482. Bark, L.S., Moran, D. and Percival, S.J. (1975). Chemical changes in asbestos-based friction materials during performance - a review. Wear, 34, 131-139. Bates, T.F. and Comer, J.J. (1957). in: Proc. 6th Nat'l. Conf. Clays and Clay Mineralogy, Inti. Monog. Sec., 6, 237-248. Bayer, S.G., Brora, T.A. and Zumwalde, R.D. (1975). Document TR-84, U.S. Department of Health, Education and Welfare, Public Health Service, National Institute for Occupational Safety and Health, Cincinnati, Ohio. Berry, E.E. (1971). Thermal analysis of various chrysotiles using evolved water analysis techniques. In: Proc. 2nd Inti. Conf. Physical-Chemical Asbestos Minerals, Louvain Univ., 6-9 September, 1971, paper 2:7 15 p. Biological Effects of Asbestos (1965). (I . J.' Selikof f and J. Churg, Eds.), Ann. N.Y. Acad. Sci. 132(1), 766 p. Boillat, M.A., Lob, M. (1973). Risk of asbestosis in workers employed in replacing automobile brake linings. Schweizerische Medizinische Wochenschrift. 103(39):1354-1359. Bouhuys, A. (1975). Fibers and fibrosis. Ann. Intern. Med. 83(6), -898-899. Bragg, L. and Claringbull, G.E. (1965). The chrystalline state. In: "Crystal Structures of Minerals" (L. Bragg, G. Bell and Sons, Ltd., Eds.), Vo).IV, London. Brindley, G.1V. and Hayami, R. (1965). Mechanism of formation of forsterite and enstatite from serpentine. Min. Mag., 35, 189-195. Burwel), J.T. (1957). Survey of possible mechanisms. Wear, 1, 119-14). Carroll, W.G. (3962). The manufacture of brake linings. British Plastics, August, 414-417. Cast)eman, B., Camarota, L.A., Eritsch, A.J., Mazzocchi. S. and Crawley, R.G. (1975). The hazards of asbestos for brake mechanics. Public Health Reports. Vol. 90 No. 3:254-256. 8005 1885 PRODUCED BY FORD 19- Daykin, C.W. (1971). A study of the infrared spectra of chrysotile and .related minerals. In: Proc. 2nd Inti. Coni. Physical-Chemical Asbestos Minerals, Louvain Univ., 6-9 September, 1971, paper 2:6, 7 p. Davis, J.M.J. (1965). Electron-microscope studies of asbestosis in man and animals. Ann. N.Y. Acad. Sci. 132, 98-111. Harries, P.G. (1968). Asbestos hazards in naval shipyards. Ann. Occup. Hyg. 11, 135-145. Harris, A.M. (1971). The effects of grinding on the structural and thermal properties of chrysotile asbestos fibers. In: Proc. 2nd Inti. Conf. Physical-Chemical Asbestos Minerals, Louvain Univ., 6-9 September, 1971, paper 3:2A, 6 p. Hatch, D. (1970). Possible alternatives to asbestos as a friction material. Ann. Occup. Hyg. 13, 25-29. Hickish, D.E. and Knight, K.L. (1970). Exposure to asbestos during brake maintenance. Ann. Occup. Hyg. 13, 17-21. Hilscher, W., Sethi, S., Friedrichs, K.H. and Pott, F. (1970). Zusammenhange Zwischen Asbestose and Faserlange. Naturwissenschaften. 57, 356. Holt, P.F., Mills, J. and Young, D.K. (1964). The early effects of chrysotile asbestos dust on the rat lung. J. Path. Bact. 87, 15-23. Holt, P.F., Mills, J. and Young, D.K. (1965). Experimental asbestos with four types of fibers: importance of small fibers. Ann. N.Y. Acad. Sci. 132, 87-97. Jacko, M.G. and DuCharme, R.T. (1973). Brake emissions: emission measure ments from brake and clutch linings from selected mobile sources. EPA Beport. 68-04-0020. Knight, K.L. and Hickish, D.E. (1970). Investigations and alternative forms of control for dust generated during the cleaning of brake assemblies and drums. Ann. Occup. Hyg. 13, 36-39. Danger, A.M., Mackler, A.D. and Pooley, F.D. (1974). Electron microscopical investigation of asbestos fibers. Envir. Hlth. Persp. 9, 63-80. Danger, A.M. and Pooley, F.D. (1973). Identification of single asbestos fibers in human tissues. In: Proc. Inti. Conf. of Biological Effects of Asbestos (P. Bogovski et al_. Eds.), pp. 19-25. I.A.R.C., Lyon, France. Lee, G.L. (1970). Removing dusts from brake assemblies during vehicle ser vicing--alternative cleaning methods. Ann. Occup. Hyg. 13, 33-36. Lynch, J.R. (196S). Brake lining decomposition products. Control Assoc., 18, 824-826. J. Air Pollution McConnell, J.D.C. (1967). Electron microscopy and electron diffraction. In: "Physical Methods in Determinative Mineralogy" (J. Zussman, Ed.), pp. 335-370. Academic Press, New York. 8005 1886 PRODUCED BY FORD Martinez, E. (1966). Chrysotile asbestos: relationship of the surface and thermal properties to the crystal structure. Can. Mining and Metall. Bull., 69, 414-420. Mizutani, y., Obara, H., Nakajima, K. (1973). X-ray study of friction and wear of resin-bonded asbestos. Wear, 23, 387-392. Monkman, L.J. (1973). Some chemical and mineralogical aspects of the acid decomposition of chrysotile. In: Proc. 2nd Inti. Conf. Physical-Chemical Asbestos Minerals, Louvain Univ., 6-9 September, 1971, paper 3:2, 9 p. Morgan, A., Holmes, A. and Lally, A.E. (1971). Solubility of chrysotile asbestos and associated trace metals in IN HC1 acid at 25C. In: Proc. 2nd Inti. Conf. Physical-Chemical Asbestos Minerals, Louvain Univ., 6-9 September, 1971, paper 2:8, 13 p. Nicholson, W.J., Rohl, A.N. and Ferrand, E.F. (1971). Air pollution in New York City. In: Proc. 2nd Inti. Clean Air Congress. (H.M. Englund and W.T. Berry, Eds.), pp. 136-139. Academic Press, New York. Naumann, A.IV., and Dresher, W.H. (1966). The influence of sample texture on chrysotile dehydration. Amer. Mineralogist. 51, 1200-12)1. Newhouse, M.L. (1965). Epidemiology of mesothelial turners in the London area. Ann. N.Y. Acad. Sci. 132, 579-602. Pott, F., Huth, F. and Friedrichs, K.H. (1972). Tumors of rats after i.p. injection of powdered chrysotile and benz[a)pyrene. Zbl. Baht. 1. Abt. Orig., 155, 463, . .......................................... Selikoff, I.J., Churg, J. end Hammond, E.C. (3964). Asbestos exposure and neoplasia. JAMA. 188, 22-38. Selikoff, I.J., Bader, R.A. , Bader, M.E., Churg, J. and Hammond, E.C. (1967). Editorial: Asbestosis and neoplasia. Amer. J. Med. 42(4), 467--196. Selikoff, I.J., Hammond, E.C. and Churg, J. (1968). Asbestos exposure, smoking and neoplasia. JAMA. 204(2), 306-112. Selikoff, I.J., Hammond, E.C. and Churg, J. (1972). Carcinogenicity of amosite asbestos. Arch. Env. Hlth. 25, 183-286. Selikoff, I.J., Nicholson, V.J. and Langer, A.M. (1972). Asbestos air pollution. Arch. Env. Hlth. 25, 3-13. Vagner, J.C., Berry, G. and Timbrell, V. (1973). Mesotheliomata in rats after inoculation with asbestos and other materials. Er. J. Cancer. 28, 173. Zvyagin, B.B. (3967). Electron diffraction analysis of clay mineral struc tures (translated by S. Lyser), Plenum Press, New York. 8005 1887 PRODUCED BY FORD Table 1 Common Components of Automotive Brake Linings Binder O'v^Qa^' Phenol esin Rubber Tire scrap 4 Pitch 4 Cork t Gilsoni te-^j^^ Cashew nut^resin Boron compounds *c Fiber Reinforcer I Chrysotile asbestos (grade 4-7) -- Unaltered - Calcined - Mixed fiber Property Modifier Lead compounds Zinc compounds Antimony oxide Iron oxide Copper metal Brass chips Clay minerals Barite (BaSO.) 4 Vollastonite (CaSi03) Quartz (Si02) Cryolite (NagAlF ) Rottenstone (SiO^) Coke (C) Coal (C) C-ilsonite (C) Graphite (C) Carbon black (C) Molybdenum sulfide (MoS_) Fluorspar (CaF^) Chrysotile fiber constitutes about 50% by weight of cost automotive brakes currently manufactured in the United States. * Sec Carrol, 1952; Anderson, 1969; Anderson 1973; Bark, e_t al_., 1975. DuCharvie, 805 1888 PRODUCED BY FORD Table II benpth Distribution of Chrysotile Fibers in Brake Drum Dust Fibers counted and sized at 42.000X (all fibers have diameters frer 250? to 500? Sample 750-1500.? 1 40% 2 32 3 20 4 26 5 57 S 23 7 50 8 29 96 10 11 1500-2250? 2250-2000? 34% 23 25 37 17 9 26 30 41 6 11% 32 25 26 4 12 21 21 18 31 3000-3750? 11% 7 - 12 2 17 10 31 Total 96% 87 70 96 78 56 99 97 75 79 8005 1889 PRODUCED BY FORD Table III Asbestos Concentrations During Automobile Brake Service (fibers 5-100p in length, counted by optical microscopy) Operation Distance Blowing dust out of brake drums with compressed air Jet 3-5 ft. 5-10 ft. 10-20 ft. Number of samples 4 3 2 Fiber Concentration (fibers/ml) Mean Range 16.0 3.3 2.6 6.6-29.8 2.0-4.2 0.4-4.8 Distance from operation Background samples taken st varying distance and lapsed times. after brake drum blowing 10 ft. 20 ft. 12 ft. 50 ft. 65 ft. 75 ft. Time lapse 0 min. 0 min. 5 min. 5 min. 7 min. 14 min. Concentration (fibers/ml) 0.3 0.8 0.2 0.1 0.1 0.1 Distance Cleaning brake drums witb dry brush 1-3 ft. Background samples taken 3 minutes after cleaning brake drums with dry brush 12 ft. Number of samples Fiber Concentra td on (fibers/ml) Mean Range 2 2.5 1.3-3.6 3 0.1 0-0.2 The Dew proposed Asbestos Standard of the U.S. Department of Labor records asbestos exposure in fibers/m^, noting that a W'orkr.an might respire approximately 8m3 of air per working day, retaining an unstudied proportion of inhaled fibers. The above table omits reference to air content of fibers < 5[j in length. 8005 1890 PRODUCED BY FORD Table IV Asbestos Concentrations During Truck 3rake Service (Fibers 5-lOOp In length, counted by optical microscopy) Operation Renewing used linings by grinding Di. stance 3-5 ft. Number of samples 10 Fiber Concentration (fibers/ml) Mean Range 3.8 1.7-7.0 Background to grinding used linings Bevelinc: new linings 10 ft. 25 ft. 60 ft. ^ .. 3-b It. 2 1.5 1.2-1.7 2 0.8 0.6-1.0 1 0.2 -- 5 37.3 2 3.7--72.0 Background to 8 ft. 1 0.6 beveling new 12 ft. 2 0.4 0.3-0.5 linings 30 ft. 1 0.3 Punching rivets into brake 3-5 ft. 2 1.5 1.9-2.0 3isings Chipping rust off used brake linings 3-5 ft. 1 2.4 Sweeping floor 3-5 ft. around grinder -. 1 3.6 --- Background to sweeping floor 15 ft. 1 3.1 around grinder 8005 1891 PRODUCED BY FORD Table V Comparison of Optical and Electron Microscopic Tiber Counts Operation 1. Blowing dust off drum with air jet (10 It. away) 2. Background to blowing out brake drum (10 ft. away) 3. Blowing dust off drum with air jet (20 ft. away) 4. Background to blowing out brake drum (20 ft. away) 5. Background to blowing out brake drum (65 ft. away 7 minutes after blowing stopped) 6. Cleaning brake drum with hand brush 7. Light grindings of new linings before installa tion . 8. Light grinding new linings beiore installation Optioal Microscopy (fibers/ml) 2.0 0.3 0.4 0.8 .1 3.6 4.7 2.7 Electron Microscopy ug/m3 1.27 0.2 1.1 0.1 0.2 6.5 53.0 66.0 8005 1892 PRODUCED BY FORD Figure 1. Electronphotmicrograph of large chrysotile bundle in brake drum dust (50,000x magnification). Other particles include phenol resin binder and road dust debris. 8005 1893 PRODUCED BY FORD 4- * t = ,* J Selected area electron diffraction patterns obtained on fibers of chrysotile oX V. v.cft'uifht- during air sampling at brake repair shops. Instrument used:ES a JEOL JEM- 120 U. Camera constant on screen: (LX^ = 47.17. The reciprocal a axis is marked *' a (A) 'as are the layer lines in the (Okl) series. Indexing of upper right quadrant yielded 16 reflections which were indexed(insert in A). Pattern in (B) displays "smearing" of reflections in a "clockwise" manner suggesting interplanar rotation. I I/ I 8005 1894 PRODUCED BY FORD figure 4 Removal of dust from brake drum and back plate by pneumatic air blowing at automobile garage. 8005 1895 PRODUCED BY FORD O'iMaT'* Fig. Beveling of truck^brakiee linings at municipal garage. AA:rrow indicates accumulation of asbestos dust. "jf JUsUfjJ CvS Ly /k 1 8005 1896 PRODUCED BY FORD Fig. 6 Renewing of municipal truck brake linings by light grinding to remove grease and dirt. S^-r, yt/juc, J fUu* pyJL* x/j svo fjuv-i, 8005 1897 PRODUCED BY FORD I tiS^rr,.. v ? rv-i: A* _ t / i- syls'- >-^'.{.VJ-' *r r- , !>'*"" '$*) ".a u t*>w t V, ,.. ft>'V</ov'.* . - ^ T7^j* . >.v>.v. ~ : '^*1 fear: \v. \ . K<i v v-v vy Sj'. - ^s. - t ^f-,. /-'V * yv '/S^-cV^T :-rf ^. c^U .. - \ //'' ; ?- W*> lif> ;/* ;-'^\ ' O*f**--' , **7 XS^ic.-i.y >;/ w 'uzy-r't .O^'*;. '.'= 'v-X--*- . '*". ^ '.`v r.,/, -f.' ! I 1 <3 - ^*v1 i Fig. 7 Electron photomicrograph of air sample taken during brake drum blowing ( sae sample # 4, Table V ) , Large numbers ( 70 )00) of chrysotile , some of which are masked by granular particulates, presumably road dust. ( 87, 000 total magnification ) 8005 1898 PRODUCED BY FORD h ' tea- /> - 5*j A \ , #fit \igv - f //W / ' ' :$is *J. I </7// v - V - - ' Aj*. 0.5 p ij Fjpure 8 Flectronmicrograph of air sample of cluster of chrysotile fibrils in background "sample (see sample "3, Table V, 110,000x magnification). 8005 1899 PRODUCED BY FORD -COMPARISON OF O P T IC A L AND EM F IB E R COUNTS AUTOM OBILE BRAKE L IN IN G S E R V IC E -M ICRO G RAM S/CUBIC METER ELECTRON MICROSCOPY PRODUCED BY FORD