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Jeremiah R. Lynch National Center for Urban and Industrial Health Brake Lining Decomposition Products A number of investigators have found asbestos bodies in the lungs of urban residents who were not oc cupationaliy exposed to asbestos. A relationship between the carinogenic 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 os free fiber while the remainder was transformed into some other, nonfibrous, mineral. A significant release of free fiber occurred only under conditions extreme enough to produce brake failure. Table I. Asbestos bodies in human lungs. Location % Year Positive Cape Town (2) Miami (2) Pittsburgh (3) Johannesburg (4) Finland (5) Montreal (6) San Francisco (1) 1963 26 1965 27 1965 41 1965 39 1966 56 1966 48 1966 42 Tabla II. Brake lining composition. Ingredient Automobile Truck Asbestos Resins and polymers Oxides and pigments Metals Carbon, graphite, etc 55 28 9 3 5 m% 33 48 16 2 1 100% Mr. Lynch is Chief of the Lab oratory of Engineering, Occupa tional Health Program, Public Health Service, Department of Health, Education, and Welfare, 1014 Broadway, Cincinnati, Ohio 45202. *?l The occurrence of coated fibers re ferred to as "asbestos bodies" in the lungs of urban populations not oc cupationally exposed to asbestos has been noted by several investigators. The results of several autopsy series, as summarized by Cooper,1 are shown in Table I.1-* Thompson,1 in suggesting possible modes of exposure that could account for these bodies, stated: The average private motor vehicle wears out three or four sets of brake linings and one or two dutch 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. Since asbestos has been implicated as a carcinogen* and lung cancer has a higher incidence* among urban popula tions, the fate of the asbestos worn from brake linings becomes significant Brake Lining Composition The average composition of typical brake linings of the type tested is shown in Table II. Individual mixes may vary considerably from these averages. Each of these ingredients performs a particular function. The asbestos pro vides strength, heat resistance, and selec tive decomposition under stress. The resins and polymers hold the other in gredients 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 while carbon and graphite serve as friction modifiers. Brake lining quality depends to aL extent on the type of binder Linseed oil, which begins to deeon at about 450F, is used for light j brakes. More demanding service^ quires brakes made from cashew, resins or oil modified phenolic These ingredients are mixed, either! or with a solvent added, formed hi shape, and cured in an oven, hardened lining is then cut, ground, i sanded to the precise dimensions of I finished linings. The dust produeedjj the abrading operations in friction product factories (Fig contains free asbestos fibers similar to those in industries wberej cer is known to be in excess." question to be resolved, therefo whether the . dust produced byrj normal wear of brake linings this same type of free asbestos i Test Methods In an initial exploratory i dust obtained from inside brake drums removed for brake: was examined by electron Figure 2, which is typical of the j does not reveal any free fibers, ever, this finding did not i possibility that free asbestos 1 released and that they had < the atmosphere. To examine pothesis a series of experiinentj devised to permit sampling i ' _ tion products of the lining underj lated operating conditions. (Table III) were performed wit brake testing machines in the i ' of a major brake lining manufe Meet of the tests were perfo HWBUI0006668 Table III. Test results by electron micrograph. Test Product Brand Method Presence No. of Conditions of Free %'Free Samples Of Test-F Fibers Fiber* l Automobile A Friction drum brakes z. Automobile s Friction drum brakes 3. Automobile c Friction drum brakes 4. Automobile c Friction drum brakes 5. Automobile 0 Friction drum French brakes S. Automobile E Friction drum brakes 7. Automobile F Friction drum German brakes S. Automobile G Friction drum brakes 9. Automobile S Friction drum brakes 10. Automobile H Friction drum .brakes a. 'Automobile J dutch Dynamometer 12. Automobile K Dynamometer disk brake 13. Bus drum l Dynamometer . brake 14. Sui drum M Friction brake IS. Truck drum F Friction brake (light) 6 300 - 800 Faw <1 6 230 - 800 None 0 5 300 - 700 Few <1 1 700 - 900 Numerous -10 5 300.800 Few <1 S 300.-700 Few <1 5 300 - 800 Few <1 2 100 - 500 Few d 1 600 . 700 Numerous -15 2 100 - 600 Few <1 1 Normal driving i Normal driving l City ^driving 2 450 - 550 10 300-800 None Few None Nona F#w 0 <5 0 0 <1 Weignt estimated from fiber volume. Some independent experiments done at a brake lining research laboratory11 have shown that all of the magnesium present in the chrysotile asbestos orig inally in the lining can be accounted for in the decomposition products. How ever, the characteristic X-ray diffrac tion pattern of chrysotile asbestos had vanished. Thus, it is apparent that under conditions in which asbestos is worn from the lining of a brake, the asbestos is destroyed. Conclusion Only a very small proportion of the asbestos worn from brake linings is released as free fiber; the remainder is converted into some other mineral as a result of the extreme temperatures gen erated at small spots on the lining sur face. Thus, although urban air con tains a few free fibers aa a result of brake lining wear, they represent a very small 82C proportion of the total asbestos used in manufacture of brakes. Many sources of respirable fibers not associated with asbestos products have been identi fied,11 and free fibers from brake lining wear seem to be an inconsequential health factor in urban air pollution. References 1. Cooper, W. C., "Asbestos as a hazard to health," ArcA. of Ena. Health. IS: 2SS (1967). 2. Thomson, J. G., Kaachula, R. 0. C., rod McDonald, R. R., "Asbestoais as a modem urban hazard," 3. Afr. Med. /. 37: 77 (1963). 3. Cauca, D., Totten, R. S., and Gross, "Asbestos bodies in human lunn at autopsy," JAMA, 192: 37 (1965T 4. Webster, I., in discussion of Thomp son, 3. "Physiological effect of D0 in mammals," Ann. X Y. AeatL SeL, 84: 736 (1960). 5. Meutman, L, "Asbestos bodies and pleural plaques in a Finish series of autopsy eases," Acta Path Microbiol. Sand Suppi., 181: 107 (1966). 6. Aryilrel, L. and Thurlbeck, IV., The incidence of asbestos bodies in the lungs of randon autopsies in Montreal, Canada. Med. Auoc. J., 93: 1179 U9W/. 7. Thomson, J. G., "Asbestos and he -irban dweller," Ann. X 1". Aca-J. Set-, 132:196(1965). 8. Selikoff, I. J., Churg, J., and Ham mond, E. C-, "Asbestos exposure sad neoplasia," JAMA, 188 : 22 (1964). 9. Buell, P. and Dunn, J. E., "Relative impact of smoking and air pollutios on lung cancer," AreA. of Eta. Health, 15:291 (1967). 10. Enttrline, P. E. and Hendrick, M A, "Asbestos dust exposures at various levels and mortality," Arch. Em. Health, 13:181 (1967). 11. Sinclair, D., "Study of wear dust from . brake lining" Johns-Manvilla Res ana Eng Ctr., personal eommusueauoiw (1967). 12. CraUey, L. S,, Keenan, R. G-, Ly J. R., and Lainhart, W. S., and identification of respirable L Amur. Ind. Hyg. Assoc. J., 0968). Journal of the Air Pollution Control Associatfo** HWBUI0006669