Document 2RdLeqN56maEEj4yjX0GGDb4R

THIS DOCUMENT WAS NOT A RFrnpn nc STM(T o F"ILES ANDIECSA'NINNCO"T~" EE AUTHENTiraiocnM by PBS INDUSTRIES, INC. UrHENTICA1E0 f 10TE: THIS I -- U ` c i j f,,, f '-. " COME FROM PPG Files Jwvfflioh R. Lynch National Center for Urban and Industrial Health * -.*e Brake Lining FILE copy Decomposition Products 1/ A number of invwtigaton have found asbestos bodies in the lungs of urban residents who were not oc cupationally 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. Broke 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, nonfibrous, mineral. A significant release of free fiber occurred only under conditions extreme enough to produce brake failure. I Table L. Asbestos bodies in human lungs. Location Cape Town (2) Miami CD Pittsburgh (3) Johannesburg (4) Finland (3) Monti eel (6) San Francisco (!) Year 1963 190 190 190 190 190 190 % Positive ' 36 27 41 39 a 41 42 Table 0. Brske lining composition. ingradlant AutomoMe Thick Asbestos fttvins md pdynurt Oxides and p^nunti fcfcttMa Carbon, graphite. ate. 0 29 9 3 9 TS5% 33 49 15 2 1 Mr. Lynch is Chief of thg Lxboretrey of Finginearing, Occupebond Heslth Program, Public Health Service, Department of Health. Education, sad Welfare, 1014 Broadway, Oncmnsti, Ohio Hie occurrence of costed fibers re ferred to as "asbestos bodies" in the lungs of urban populations nut oc cupationally exposed to asbestos has been noted by several investigators. The results of several autopsy aeries, aa summarised by Cooper,1 are shown in Table L1-4 Thompson,' in suggesting possible modes of exposure that could aoeount for these bodies, stated: Tbs avenge private motor vehicle wean oat three or four sets of brake linings sad an* or two dutch Hnings in its liferime, end wnmedsl tad public transport vehicles wear out many more. ThaMlmina consist largely of asbestos which is ground to dust as the linings weer-and most wear occurs m built-up mss. This alone in most arias would involve the discharge of many tons of asbestos doss and fibsre in the streets eachyeer. Since asbestos hag been implicated aa a raremofen4 and lung cancer haa a highs' incidence* among urban popula tions, the fate of the asbestos worn from brake hoomrinn significant Brake Lining Composition The average composition of typical brake finings of the type tested is shown in Table IL Individual mixes may vary considerably from these averages. Each cf there 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 cf the lining on the drum. Soft metals such as lead and brass improve wear while carbon igh^te serve aa friction modifiers. Brake fining quality depends to a large extent an the type of binder used. Linseed oil, which begins to decompose at about 450F, is used far fight service brakes. More demanding service re quires brakes made from cashew type reams or oil modified phenolic resins. There ingredients are mixed, either dry or with a solvent added, formed into shape, and cured in an oven. The hardened lining is then cut, ground, and sanded to the precise dmwminni of the finished linings. The dust produced by the abrading operations in asbestos friction product factories (Figure 1) contains free asbestos fibers that are similar to there in industries where can cer is known to be in excess.- The question to be resolved, therefore, is whether the dust produced by the normal wear of brake lining* contains this same type of free asbestos fiber-- Test Methods In an initial exploratory survey, the doit obtained from inside automobile brake drums removed for brake refining waa examined by electron micrograph, figure 2, which is typical of the series, does not reveal any free fibers. How ever, this finding did not eliminate the possibility that free asbestos fibers were released and that they had escaped into the atmosphere. To this hy pothesis a serin of experiments wee devised to permit sampling decomposi tion products of the lining under simu lated operating conditions. The teste (Table HI) were performed with the brake testing machines in the laboratory of a major brake lining manufacturer. Most of the teste were performed on a BB 0020768 | j, tel of the Air Pollution Control Association i vw im v. n..--i--. *o*v THIS DOCUMENT WAS NOT A RECORD OF PPG INDUSTRIES, INC. DID NOT COME FROM IT'S FILES AND CANNOT BE AUTHENTICATED BY PPG INDUSTRIES, INC. NOTE: THIS NOT C ?, jj r* > O i\': U. t Fleet* 2. Brake lining factory dust. Fleer* L Oust removed tram Stake drum. Hyara L Dacomoositxjn product from nor mal waar pt brake imtng. friction-testing machine which used one-ineh-square samples of the test lining- Seating and cooling apparatus permitted control of dram temperature from those encountered with inter mittent brake use to the maximum temperature which occurred only in extremely rapid or "panic'' stops from high speed. Other testa wen performed on a brake-testing dynamometer which subjected a complete brake assembly to a series of stops and starts from different speeds and at different deceleration rates to simulate actual' driving con ditions. In these tests the drum tem peratures varied according to the driv ing condition simulated. During each run at a test condition, a sample was collected cm an 0-8 m pare sixe 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. Results The object of the tests was to deter mine what proportion of the asbestos known to be present in the lining ap peared as free fiber in the decomposi tion product No attempt was made at a mass balance between the material . worn from the lining and the deeom' position product since it was not pos sible to collect all of the decomposition product However, the percentages obtained in the fraction of decomposi tion product examined are applicable to the total material worn from the brake sad may be compared to the percentage of asbestos originally present In all but a few tests the automobile December 1368 Volume IS. No. 12 drum brake linings showed less than 1% bee fiber in the decomposition product aa compared to about 50% in the lining. An electron micrograph of the decomposition product obtained from a typical test in this group is shown in Figure 3. In those testa where a sig nificant mass of free fiber was released (Figure 4), 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 Uninfp been subjected to like conditions in a vehicle, the brakes would have failed. Similar results were obtained in the bus and truck drum brake tests and in the clutch test. The experimental model disk brake tested did release some (>5%) free fibers, but no conclusion can be drawn from a angle sample. Discussion Except in all but the most extreme driving conditions, only a very small fraction of the 30 to 50% asbestos pres ent in a brake lining escapes into, tbs atmosphere as free fiber. The question remains: What happened to the as bestos? A prevalent theory of brake operation holds that wear occurs not by abrasion of the lining by the drum but by the production of minute areas of intense heat at the points of contact between the drum and the lining. De composition, not only of the binder but of the asbestos as well, occurs at these locations since the breakdown tem perature of asbestos, about 900F, is exceeded. Decomposition products will include not free asbestos fibers, but a different mineral resulting from thermal metamorphosis of asbestos. FlymwS. Oecompeertlen ptoduct trwn brake lining tfaicre- | DB Oii 20 769 j 3261 Table III- Test rwulf by electron mloograph. THIS DOCUMENT WAS NOT A RECORD OF PPG INDUSTRIES, INC. DID NOT COME FROM IT'S FILES AND CANNOT BE AUTHENTICATED Test Product Brand Metnod Presence No. of Conditions at Free Samples of Te*t-F Fibers L Automobile A drum Friction 8 300-100 Few <1 brakes 2. Automobile 8 drum Friction 8 250-00 None 0 brakes 3. Automobde C drum Friction 3 300 - 700 Few <1 brakes 4. Automobile C drum Friction 1 700 - 900 Numerous -10 brakes 5. Automobile drum rar-v-D-n--ean_ meson 5 300-00 FeW <1 brakes 6. Automobile E drum Friction 3 300 - 700 Few <1 brakes 7. Automobile F Friction drum German 5 300 - 800 Few <1 brakes L AutomobSa a m*eson_ 2 100-500 Few <1 drum brakes *. Autsnwbli Q Friction drum 1 800 - 700 Numerous -IS brakes 10. Automobile M mf 1e-srto n1 2 100-800 Few <1 drum brakes 1L Automobile J dutch 12. Automobfle K disk Dynemometar awW a anvwig 1 rtarm w* Few <3 anvwif r~^\ ivT --- i r ) lLi ^ O r'-j U. Bus drum L Dynamometer 1 aty None brake 14. Bus drum M Friction dllslug 2 450-B0 an>Q--nv 0 0 brake 13. Trudt drum F Friction 10 300-00 Few <1 brake OHM) from rtbor vfrumi. Some independent experiments done st a brake lining reeeareh laboratory11 hsre shown that all of the magnesium present in the chryaotde nsbeetoe orig inally in the lining can be accounted for in the decomposition products. How* ever, the characteristic X-ray diffiraetion psttem at chrysolite asbestos bed vanished. Thus, it is apparent thst under wmditinM in which asbestoa is worn from the lining of s brake, the asbestos is destroyed. 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 erf the extreme temperatures gen erated at small spots on the lining sur face. Thus, although urban air con* tains a few free fibers as a result of brake fining wear, they represent a very small I proportion of the total asbestos used in manufacture of brakes. Many sources at respirable fibers not iMoriatsd with asbestos products have'been identi fied,1* and free fibers from brake lining wear seem to be an inconaeqoimtiml health factor in urban air pollution- 1. Coopw, W. C, "Asbestos aa a hazard to health,'' .An*. of Eta. Eoaitk. 15: 285(1887). 2. TH**, J. (L, Tt--R. O. C,, and McDonald, R. R, "Aabeatcais as a modern urban hazard," 3. -A.fr. Mod. J. 37: 77 (1963). 3. Cauna, D., Totten, R. 3- and Groat, P., "Aabsatos bodiae in human tone at autopsy," JAMA, 192: 37 (1965). 4. Webstar, L, in djacuaainn of Thomp son, S. F_, "Physiological effect at D,0 in mammals," Ana. N. Y. Acad, Sea, 54: 738 (I960). 5. Maurman, 1*, "Aabaetoa bodies and pleural piyp'-- in a Finish tenet of autopsy easts," Ada Path MitroinoL n r Stood Stand; 151:107 (1988). & Aryibai, L. and Tburibeek, W,, "The incidence at asbestos bodies in the tunes of randon autopsies in Mootraah. (".n-rt. Mtd. A*me, J-, 95:. 1179 (1968). 7. TIwmb, J. G* "Asbestos and the ur ban dweller," Awn. N. Y. Acad. Sea, 132:198 (1965V 8. Sahknfl, L J,, Churg, J-, and Ham mond, E. C_ "Azbeatos exposure and neoplasia,"/Aifk, 1SS: 22 (1964V 9. Buril, P. and Dunn, J. R, "Relative impact of and sir pollution an lung cancer," Arch, of Eta. Eoaitk, 15 : 291 (1967V 10. Enteriine, P. E. and Kendrick, M. "Asbeatoe dust exposures at various and mortality," Arch. Eta. Eoaitk, 15:181 (1987) 1L Sinclair, DM "Study of wear dust from brake lining," Jahne-Manvilie Rea and Ea^Ctr., personal oommunication 12. CraDey, I- J., Keenan, R G., Lynch, J. R, and Lambert, W. S_ "Source and identification of reepirable fibers," Amer. Ind. Hyg. Asaoe. Jn 29: 129 (1968V bb" oo 20T70 1 3262 Journal of the Air Pollution Control Association