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h i' .I BRAKE LINING DECOMPOSITION PRODUCTS ' . .' BY Jeremiah R. Lynch -Occupational Health Program ' 1014 Broadway Cincinnati, Ohio 45202 U. S. DEPARTMENT OF HEALTH, EDUCATION*, AND WELFARE Public Health Service National Center for .Urban end. Industrial Health Occupational Health Prograte Presented at the Engineers Round Table Thirtieth AnnualKafctJ.nsr^T-'-- American Conference of ^pvlirninentRl Industrial Hygienists St. Louis, Missouri, Hay 12-, 1968 ' 012S36 JWK0Q7909 I SCF-FORD-0565 . . . ' brake lining decomposition products .. .! . * ABSTRACT - .. . . A number of Investigates have found asbestos bodies In the lungs of urban residents who were not occupationally exposed to asbestos. A relationship between the. carcinogenic properties of asbestos and the urban excess of lung cancer has been suggested. The decomposition products of brake linings have been described as a possible source of these fibers. Brake testing laboratory methods were used to test fiber emission from a variety of friction products. Only a very small fraction of the asbestos escaped as free fiber while.the remainder was transformed Into some other, non-fibrous, mineral. A significant release of free fiber occurred only under conditions extreme enough^to produce bfak^ failure. 0 1? O O*-> T JHK007910 BRAKE LINIRC DECOMPOSITION PRODUCTS A Jeremiah R. Lynch* Introduction - The-occurrence of coated fibers referred to as "asbestos bodies" - In the lungs of urban populations not occupationally exposed to asbestos has been noted by several investigators. The results of several autopsy series, as summarized by Cooper,^ are shown in Table Thomson, ^ in suggesting possible modes of exposure that could account for these bodies, stated "The average private'actor vehicle wears out three or four sets of brake linings and one or two clutch linings in its lifetime, and commercial and public transport vehicles wear cut many more. These linings consist largely of esbastos which is ground to dust as the lings wear, and most wear occurs in built-up areas. This alone in most cities .. .t would involve the discharge of many tons of asbestos dust and fibers in the streets each year." Since asbestos has been implicated as a carcin ogen (8>and lung cancer has a higher incidence^ among urban populations, the fate of the asbestos worn from brake linings becomes significant. *U. S. Department of Health, Education, end Welfare . Public Health Service . . Bureau of-Disease Prevention and Environmental Control National Center for Urban and Industrial Health Occupational Health Program ' 1014 Broadway, Cincinnati, Ohio 45202 . 01 O V.> vT-> |"> JHK007911 . .- - .. * ' -2- * . Table 1 ' '. .. - .-- -- . ' Location , Asbestos Bodies In Human Lunes ' . . Tear % Positive Cape Town (2) Miami (2) 1963 1965 26 27 Pittsburgh (3) 1965 41 Johannesburg (4) . 1965 39 Finland (5) . 1966 58 Montreal (6) . 1966 48 Saa Francisco (1) ' 1966 * 42 01 iOuOTOQ7 JWK007912 i -3- Brake Li.ning' Com position' ' ` r~ The average composition of typical brake linings of the type tested is- shown in Table 2. Individual ciixes may vary considerably from these averages. ;' ' f '. Table 2 . . . 1- Brake Lining Composition , . ` '' Ineredient Automobile Truck Asbestos Resins and Polymers Oxides and pigments Metals Carbon, graphite, etc. jr.v-y 55 28 9 3 5 1007. . 33 48 16 2 1 1007. Each of these ingredients performs a"particular" function. The asbestos provides strength, heat resistance and selective decomposition .* -v under stress. The resins and polymers hold the ocher ingredients together. Various oxides are added as pigments and to improve the grip of the lining on the drum. *. . Soft. metals such as lead and brass improve wear vhlle . carbon and graphite serve as friction modifiers. Brake lining quality depends to a large'extent on the type of binder " OH.O . . used, . Linseed oil, which begins to-decompose at about A50 F-, is used for light service brakes. More 'demanding service requires brakes made from cashew type resins or oJ modified phenol it resins."... jThese ingredients* are . mixed, either dry or with a solvent added," formed, into- shape and cured' - 012S40 JUK007913 -4- in an oven. The hardened lining is then cut, ground and sanded to the precise dimensions of Che finished linings. The dust produced by the abrading operations in asbestos friction product factories (Figure 1) contains free asbestos fibers thap are similar to Chose in Industries . `I where cancer is known to be in excess (10). The question to be resolved, Itherefore, is whether the dust produced by the.normal wear of brake linings contains this same type of free asbestos fiber. - Test Methods '' ' . In an initial exploratory survey, the dust obtained from Inside automobile brake drums removed for brake relining was examined by electron micrograph. Figure 2, which is typical of the series, does not reveal any free fibers. However, this finding did not eliminate the possibility that free asbestos fibers were released and that they had escaped into the atmosphere. To examine this hypothesis a series of experiments as devised to permit sampling decomposition products of the lining undjr simulated operating conditions. The tests (Table 3) were performed with the. brake testing machines in the laboratory of a major brake lining manufacturer. Most of the tests were performed on a friction-testing machine which used one-.lnch-square samples of the test lining. Heating and cooling apparatus permitted control of drum temperature from those., encountered with intermittent brake use to the maximum temperature which .occurred only in'extremely rapid or.J'panic" stops f rom'high'speed-. : ' Other tests were performed on a brake-testing dynamometer which subjected 012841 JWK007914 i -5- a complete brake assembly to a.series of stops and starts from different speeds and at different deceleration rates to simulate actual driving - conditions. In these tests the drum temperatures varied according to the driving condition simulated. During each run at a test condition, a sample was 'collected on an 0.8 ji pore sire membrane filter. Electron micrographs of these' filters were examined to determine the presence of free asbestos fibers and to quantify these fibers when more than a few occurred. . ' 012342 JWK007915 ' -6- - . Table 3 .. . Test Results by Electron Micrograph Product Brand 1. Automobile *A drum brakes1 2. , fl B 3. If C 4. * C 5. II . D French 6. tl E 7. M - F German 8. M G 9. ' It G 10. II H Test. Method Friction Friction Friction Friction Friction No. of Samples { 6 1 1 ,6 5 1 5 Conditions Presence of of Test-F Free Fibers 300-800 Few 250-800 300-700 700-900 300-800 None Few Numerous Few X Free Fiber* <r 6 <i --10 <i Friction Friction ' 5 5 300-700 300-800 Few Few <i <i Friction Friction Friction 2 . 100-500 Few 1 600-700 Numerous 2 100-6C0 Few <i --15 <1 11. Automobile clutch J Dynamometer 1 norasl driving None 0 12. Automobile ' disk brake K Dynamometer 1 normal driving Few <5 13. bus drum breke L -Dynamometer 1 city driving None 0 14. M x Friction 2 450-550 None 0 15. Truck drum F- ' brake (light) Friction ' . 'io' - : ~;'300-800 -- . Height estimated from fiber volume. ' riu y::; y <:i;' 012S43 JWK007 91 6 -7- Results . ' ' The object of the tests was to determine what proportion of the asbestos known to be present In the lining appeared as free fiber in the - decomposition product. No attesfit was made at a mass balance between the material worn from the lining andjthe decomposition product since It was not possible to collect all of tile decomposition product. However, the percentages obtained in the fraction of decomposition product examined are applicable to the total material worn from the brake and may be compared to the percentage of asbestos originally present. In all'but a few tests the automobile drum brake linings showed less than IX- free fiber In the decomposition product as compared to about . * $0Z In the lining. An election micrograph of.the decomposition product obtained from a typical test in this group Is shown In Figure 3. In those tests where e significant mass of free fiber was released (Figured), the temperature was In an extremely high range for the lining In question as evidenced by rapid drop In the coefficient of friction. Had these linings been subjected to like conditions In a vehicle, the brakes would-have- failed. . . Similar rcsults'werc obtained In the bus and truck drum brake tests and in the clutch test. The experimental model disk brake tested did releese some (>57.) free fibers, but no conclusion can;be drawn from..a single sampled . ' ' . .* \ A~\;. 5" 012S44 JWK007917 ` -8- . Discussion .. - Except in all but the most extreme driving conditions, only a very snail fraction of the 30 to 50Z asbestos present , in a brake lining escapes Into the atmosphere as free fiber. The question remains: What happened to the asbestosf A prevalent theory of brake operation holds that wear occurs not by abrasion of* the ling by the drum but by the I . production of minute areas of intense heat at the points of contact between the drum and the lining. Decomposition, not only of the binder but of the asbestos as well, occurs at these locations since the break- . down temperature of asbestos-, about 900T F. Is exceeded,. The decomposition products will thus Include not free asbestos fibers, but a different mineral resulting from the thermal metamorphosis of the' asbestos. ; Some Independent experiments done at a brake lining research labotatory^^ have 6ho*m that all of the magnesium present in the . .. . . - .v, chrysotile asbestos orglr.ally In the lining can be accounted for in the decomposition products. However, the characteristic X-ray diffraction pattern of chrysotile asbestos had vanished. Thus, it is apparent- that under conditions in which asbestos is worn from the lining of a brahe^ the asbestos is' destroyed.' Conclusion . .. . Only a very small properticn of the asbestos worn from brake . linings la released as free.fiber; the'remairid.er ie converted into.'pome.- other mineral as a result of the extreme temperatures generated at small spots on the lining surface. Thus, although urban ai.r-.contains a-few 01 2S4 JUK007918 9' - - free fibers as a result of brake lining wear, they represent a very small, proportion of the total asbestos used in the canufacture of brakes. Uany sources of respirable fibers not associated with asbestos products have been identified, t' t and the free fibers - from brake lining wear appear to be an inconsequential health factor .I in urban air pollution. 1 . - i i 012S46 JWK007919 10 - References 1. Cooper, V. "C.: Asbestos as a Hazard to Health. Arch, of Cnv. Health. 15:285 (19611. . ' . ' 2. Thomson, J. C., R. 0. C. Kaschula and R. R. McDonald: Asbestosls as a Modern Urban Hazard. S. Afr. Med. J. 37:77 (1963). 3. Cauna, D. R. S. Totten and P. Cross: Asbestos Bodies in Human Lungs at Autopsy. JAMA 192:37 (1965). " A. Webster, I'., in discussion o Thompson, S. F.: Physiological Effects of D20 in Mammals, Ann. N. Y. Acad. Sci. 84:736 (1960). . 5. Meurman, L.: Asbestos Bodies end Pleural Plaques in a Finnish series of Autopsy Cases, Acta Path Microbiol Scand Suppl 181:107 (1966). Aryllrel, L. and W. Thurlbeck: The Incidence of Asbestos Bodies in the Lungs of Random Autopsies in Montreal, Canada. Med. Assoc. J. 95:1179 (1966). .. .7. Thomson, J. G.: A.sbestos and the Urban Dveller. Ann. N. Y. Acad. ,;Sci. 132:196 (1965). ' 8. Ssllkaff, I. J., J.Churg and E. C. Hammond-; Asbestos Exposure and Neoplasia. JAMA 188:22 (1964). ' *' 9. Buell, P. and J. E. Dunn: Relative Impact of Smoking and Air Pollution on Lung Cancer. Arch, of Env. Health 15:291 (1967). . 10. Enterline, P. E..and M. A. Kendrick': Asbestos Dust Exposures at Various Levels and Mortality. Arch. Env. Health 15:161 (1967)." 11. Sinclair, D.: Study of Wear Dust from Brake lining. Johns-Manvilie Research and Engineering Center, personal communication (1967). 12. Cralley, L. J., R. C. Keenan, J. R. Lynch and W. S. Lainhart, M.D.: Sources.' and Identification of Respirable Fibers". Am. Indust. Hyg. Assoc. J.'29:2 (1968). .. 0I2S4 JWK00 7 920 Figure I. Brake lining factory dust. 012S4S JWK007921 o l>.">; - v f i* ;. ; * 6 o r ^ C7 V \ * &gf' ;KJ . i . *k' >. * ~J ' : o* a (3 >* *> ^~TY\\ . aA * v <? *v> ' D. - * j? * * >" * J* a vf r* ' O1 vV,,vl ` '. Ox ' * >' I I d_ J7-J ^ ^ / >o C .'-A'-;; o` *~\ n '-`v Vc V'r*."S ro - ,*$ c * - n " * *. -{3J s- c. % f"? ^ 'o O vc?c`$ ;0- cr <j- V , 5 D '-, r--' Q 'VS lv> ^ "^3 \t> ':> r V 'V^/ >> /7 //V^ r, ' J- X'/"<.-. '-N\ * >s. a ,*. - --y v * ^ . 4 r-X * *r :' l r; o <5'C-^ *o rN '\ : ci'. I/4. i b . ... **.. . . vr S. t.'^ : Figure 2. Dust removed from brake drum; 912S43 JWK007922 s Figure 3. Decomposition product from normal-wear - ~ of brake lining . .. i 012S50 JWK007 923 . . Figure 4. Decomposition product from brake lining - . c at failure . - '- ` 012S51 JWK007924 2H //. COPY Public Health Service - BSS Asst, to Chief for Epidemiology and TO: Field Studies, DOH FROM: Engineering Section SUBJ: Report on Brake Decomposition Tests At the New-York Academy of Sciences Conference on the Bio logical Effects of Asbestos" it was stated: *1) "The average private motor vehicle wears out ttrree or four sets of brake linings and one or two clutch linings in its lifetime, and commercial and public transport vehicles wear out many more. These linings consist largely of asbestos which is ground to dust as the linings wear, and most wear occurs in built-up areas. This alone In most cities would involve the discharge of many tons of asbestos dust and fibers in the streets each year." This statement was meant to explain, in part, the presence of "asbestos bodies" observed in the lungs of non- occupationally exposed residents of Cape Town, South Africa, and Miami, Florida. ^ To investigate this possibility, a study of the mode of dis integration of brake shoes under simulated operating conditions was undertaken by using test facilities made available by the American Brake Shoe Company laboratory at Kahwah, New Jersey. These tests were made as part of the Division of Occupational Health's overall epidemiological study of the asbestos processing industry. . Automobile brakes are composed of from 30-50% asbestos (usu ally chrysotlle) held together with various resins and con taining such other ingredients as carbon, brass filings and rubber. Theoretically, a brake wears by abrasion of the sur- . face by the drum and by thermal decomposition of the binder. The question to be resolved was: What fraction, if any, of the asbestos is liberated as free fiber in the wearing process undesvarlo4s operating conditions. (1) Thomson, J.C.: Asbestos and the Urban Dweller, Annals of the New York Acad, of Science, VI32, Art. 1 (196-214), . Dec. 1965 An I r 011350 JUK007 833 i- T I 2 Asst, to Chief for Epidemiology and PI eld Studies, DOH -- 4/8/66 At the Kahwah laboratory a number'of brake testing dynamom eters were available which could simulate various operating conditions. These machines were set to test a variety of typical brakes and air samples of the decomposition products were taken on membrane filters. Electron micrographs were made of the deposits thus collected and a number of fields were scanned for the presence of fibers. Where significant numbers of fibers were found an estimate of the fraction of the decomposition product which was fiber was made by sizing all of the particles and fibers seen. The results of these tests are as follows: Decomposition of Brake Linings No. Type of Brake Condition of Presence % Fiber Test of Fibers (mass) 1 Disk Brake Norma!;' driving Pew <5 2 Bus Brake City driving None 0 3 Automobile 100-200 F drum Few temperature 4 Automobile Brake 300-500 P drum temperature ^0 , <1 5 Automobile Brake 600-700 F drum Numerous temperature 15 6 Automobile Clutch Normal driving None 0 7 Bus Brake 450-550 P drum None temperature 0 8 Automobile Brake 100-300 P drum None temperature 0 9 Automobile Brake 400-600 P drum Pew temperature " 10 Bum- Brake ^50-550 F drum None temperature 0 One clump of fibers still largely coated with binder and having a roughly rectangular shape. ! Xrt 011951 JWK007834 `-f. :\ }. -3- Asst, to Chief for Epidemiology and Field Studies, DOH -- 4/8/66 In only one case (No. 5) did the percentage of fiber approach the percentage of asbestos In the brake and that was at a temperature of 600-700 F as compared with normal msLXlmum operating temperatures for automobile brakes In the range of 550-600 F It appears that when the design temperature of a brake Is exceeded, the binder decomposes and releases part of the asbestos as free fiber. At lower operating tempera tures the asbestos worn off the lining remains encapsulated in the binder and few free fibers occur. Thus, although urban air would undoubtedly-contain a few free asbestos fibers as a result of disintegrating brake shoes, they would represent an extremely small percentage of the total asbestos used In the manufacture of brakes. Jeremiah R. Lynch Senior Sanitary Engineer Engineering Section Research and Technical Services Branch 011952 JWK007 835