Document QMkEaeDLvQo9xR7DJKMLM8LzL

FILE NAME: Abex (ABX) DATE: 1972 June 6 DOC#: ABX189 DOCUMENT DESCRIPTION: Memo to Members of Asbestos Study Committee RE Asbestos Fibers Emissions-Friction Materials with June 19 Cover Memo AMERICAN B R A K E B LO K D IVISIO N W IN CHESTER O FFICE MEMORANDUM June 19, 1972 SUBJECT: ASBESTOS FIBE R S EMISSIONS - FRICTION M A TER IA LS The en clo sed m ailin g fro m the FM SI A sb esto s Study C om m ittee is of great in terest now that the E PA E m issio n study report is about to be relea sed . Note the item on " B rak es" , page 28. The assum ption appears to be that d isc b ra k es w ill be the "cure all" . We w ill attend the next m eetin g of the com m ittee and w ill report further findings. E. H. Feierabend E H F /le cc: M e ssr s. G. L. R om ine D. K. R ennie S. M. A ndrichak C. H. B orcherding. Jr. ' G. R. G raham J. J. Sheffield F. E. T ayler, Jr. A. M. Unger F ile SP NY 006096 -'FRICTION MATERIALS ST "'ARDS INSTITUTE, INC., E-21Q ROT'' 4, PARAMUc^J N. J. 07(v June 6, 1972 TO: Members of Asbestos Study Committeet SUBJECT: Asbestos Fibers Emissions - Friction Materials A seminar was held at the Illinois Institute of Technology Research Insti- ^ ^ e / a f t e r ^ n u a r , 1, and sold for use in Illinois." The pages from the IITRI paper are: pages 22, 25, 26, 27, 28, 6, 49, 65, 66, 67, 68, 69, 70, 71, 72, 73. Your Chairman, Mr. I. H. Weaver, sent this data to me for di^tJ'ibuttj?1?. t the Committee. He commented on the paper: "J'h ^ l"r1* ^ etheWree fibers or * H b r U s 're?easldSf?omWfrlot'ion^tefia7decomposition are truly hazardous in any wiy' and t believe he tends to underestimate the problems in non-asbestos containing braking systems. " Your Chairman boliaves that a acting of 1 O o i t t stouW oj^ed^ I'm asking for a reply on the attached form, for which w ^ k s n^t to f l U j ^ t i n g. From this I will try to arrive at a meeting date (perhaps late July or 1 August). ' EWD/lmc E. IV. Drislane Executive Secretary U N 2 i 1972 A.BEX CORPORATION m ed ical dept SPNY 006097 attachments such that the dust created is arrested at the s o u r c e and collected in filter bags. Commercial devices are available but normally firms with a sincere interest in pollution control, design and fabricate their own devices. Two examples of such ^ devices are shown in Figures 6 and 7. These control hoods work on the high velocity, low volume principle and can be readily adapted to industrial vacuum cleaner systems. When arrest-at-the-source systems are not possible, tech niques similar to those employed by the asbestos spraying industry may be utilized. Rules which relate more specifically to fabrication of- asbestos products may be found in such publi cations as: , . . 1. "Recommended Practices for Fabricating, Handling and Construction Industries," Health and Safety . Council-Asbestos Cement Products Association. 2. "Recommended Health Safety Practices for Handling ,, and Applying Thermal Insulation Products Containing Asbestos,". National Insulation Manufacturers ' - Association (NIMA) . . . 3. The Asbestos Research Council - Control and Safety ' Guides (London, England). 4. "Recommendations for Handling Asbestos," Engineering Equipment Users Association (EEUA), E.E.U.A. Hand book No. 33. . 3.3.3 Friction Material Applications . 1 " . . *' . * Typical friction materials contain 30 to 50% asbestos and may be up to 70%, and the industry that manufactures these ma terials is ranked third (19&9). in the consumption of asbestos fibers. Crysotile is the preferred variety because it has better frictional properties than amphibol asbstos and does nt exert so much wear on the opposing surface. . sThe. major uses of asbestos-co*ntaining friction materials * include^brake linings, brake discs and clutch facings. These product's have been applied to a wide variety of industrial and commerqial products. ' -r;: ' I IT R E SE A R C H IN STITU T E . 22 SP NV 006098 Sources of Emission - Emxssion of asbestos from friction materials results from normal day-to-day usage. An idea of the scope of this source can be gained from the estimation that the t * - average automobile wears out 3 to 4 sets of brake linings, and 1 to 2 sets of clutch facings during its lifetime and that commercial public transport vehicles wear out many more sets. Data concerning motor vehicle brake linings for the whole of the United States are given in the following: Vehicle miles during 1968 Mileage life of brake linings Brake lining sets on new vehicles Pounds of asbestos per set ol brake linings 1 ,010,00 0 ,000,000 27,500 10,718,000 ' 3 ' Tests, performed on brake linings have indicated that . under conditions of normal usage, considerable alteration of the asbestos occurs. It is reported that most of the dust collected from brake drums appears non-fibrous and is sxmilar in appearance to thermally degraded asbestos. The suggestion is that hxgh temperatures at the brake lining/drum contact points actually reach degradation levels. Tests on brake linings, brake discs and clutches have demonstrated that the quantity of fiber emitted is some function of the severity of the braking conditions (see Table 3). How ever, even at the level of 1%, the total emissions must b& considerable when the total tonnage in use is considered. Further, the emissions are likely to occur at places of high density population and restricted ventilation. That is, in busy main streets of towns surrounded by large buildings. The effect of different braking conditions and different types ;of friction materials on asbestos emissions is the subject' of a study being sponsored by the Environmental Protection Ag'ency. Other studies are being conducted in California and some work on roadsides has been done at Mt. Sinai, New York.- The EPA study 11 establish the extent and nature of the asbestos IIT RESEARCH INSTITUTE 25 SPN Y 006099 Table 3 ASBESTOS EMISSIONS FROM BRAKE LININGS (Test Results by Electron Micrograph) Brand Test Method 1. Automobile A drum brakes Friction 2. II B Friction 3. It C . Friction 4. C Friction i ` II 5. ` D French Friction 6. 1 . 1 E . Friction 7. II .F Friction Gentian 8. 1 G - Friction 9. It G Friction 10. II H . Friction No. of Sampler. 6 Conditions of Test-F 300-000 6 250-800 5 . 300-700 h 700-900 5 300-000 .. 5 ` 4 , 5 300-700 300-800 2 A 100-500 1 600-700 2 ` 100-600 11. Automobile J clutch Dynamometer 1 normal driving 12. Automobile K disk brake Dynamometer t 1 normal driving 13. Bus drum brake L Dynamometer 1 \ city driving 14. M Friction 2 450-550 15. Truck drum F Friction 10 brake (light) i *Uclght estimated from fiber volume. ' '* 300-800 Presence of Free Fibers Few *None Few Numerous Few Few Few Few Numerous Few None . . Few' None None Few 7. Free Fiber* <1 0 <1 ~-io <1 <1 < 1' <1 w-15 <1 0 <5 0 0 <1 26 SPN Y 006100 emitted from brake drumc, disc brakes and clutches of vehicles operating under real conditions. Hopefully the situation will be more' clearly understood at the end of those studies. _ Emission Control Techniques '' . Emission at Overhaul - To avoid blowing the accumulated dust into the atmosphere at the time of overhaul devices have been suggested for extraction of the dust from brake and/or clutch housings by suction. Of the (devices tried, a simple hand-held vacuum cleaner has proven to be the most flexible unit. Change's to the original design have been limited to the addition of a disposable paper bag Inserted in the original cloth bag. The paper bag may be easily sealed before removal to prevent emission. 1 Substitution - Beyond the adapttion of better cleaning practices during brake and clutch maintenance, as mentioned ,, above, additional controls seem tcS be limited to improve design of brake and clutch assemblies and/or substitution of other materials for asbestos. ~ The high temperature properties and exceptional tensile strength of asbestos have resulted in v.ery compact and economi cal design. These same unique properties-which make asbestos applicable to friction materials also make the application of substitute materials very difficult. The tensile strength-'and modules of rigidity of asbestos as compared to several candidate substitute *materials'follows: Tensile Strength lb/in.^ 2 Modulus of Rigidity lb/in. Asbestos Fiber yarns Slleel wool 550,000 180,000 . 50,000 30,000., 000 3,000,000 . 100,000 Mineral wool 25,000 * , 60,000 . *'Ty * - There.is no doubt that substitution of other .materials for asbestos is*possible, but the design changes required to accom modate the stresses and temperatures involved would result in * "* : .11T R E S E A R C H INSTITUTE . ' \ 1 27 ' ' SPN Y 006101 larger, more expensive components. Brakes - The recent adoption of disc brakes by the auto motive ipdustry makes material substitution more plausible. Disc brakes are capable of greater energy dissipation than similar sized drum brakes because the design results in con siderably lower heating rates. This is due to the fact that at any one time the friction pad contacts only a section of the disc surface. The lower operating temperatures permit the use of friction materials which do not contain asbestos. Another feature of disc brake design which has reduced the need of asbestos material's is the lower strength requirement of the friction material. . * Clutches - The substitution .of other material for asbestos in clutch facings of traditional design-could only be done by changes in size and design. Two- changes in clutch design which have reduced the requirement for asbestos-containing friction' . materials are the advent of the automatic transmission and the ' redesign of manual clutch friction surface. * . The clutch surface of the automatic transmission is im mersed in an oil bath which virtually eliminates airborne - pollutants. Further, the cooling affect.of the oil bath reduces the requirement for high-temperature capability materials. Automatic transmission clutch facings may be made from either sintered metals or fibrous cellulose materials. Many manual-clutches have redesigned friction surfaces which consist of numerous small circular pads or discs attached to the clutch face as opposed to the standard annular ring friction surface. These small pads act in the same manner as the diob brakes friction pad. Thus, lower stresses and oper ating -temperature^ associated with the new design reduce the ' ' need for asbestos-containing friction materials. - - * IIT RESEARCH ' 28 INSTITUTE . . ) ---- SPN Y 006102 ] ;] 1 J ] ] j ' ]' ] 1 1 1 ] ]. 1 I i I 10. SPECIFIC PROBLEMS * 10.1 Emission Levels In understanding control techniques,and their efficiencies, it is important not to be confused with efficiencies quoted"on ^ a weight basis and those based on a particle count basis. Firstly, considering efficiency based on a weight basis, it is relatively easy to get a very high efficiency with parti cles whose size is in excess of 5 with a variety of ^control devices (see Figure 10). However, the efficiency does drop off considerably with decrease of particle size, for example, see Figure 11 for 1/r particles. (It should* be noted that these graphs refer to spherical particles^ - information on fibrous particles is not presently available.) Now consider what these apparent high efficiencies mean in terms of numbers of fibers. It can be assumed that 10^ average fibers of asbestos weigh approximately l n g . ' t - ^ ` * If 1, g of asbestos material approaches a filter rated at - even as high as 99.999% efficiency, then>the quantity passing 4 through will be 0.00001 g, or 10 ng. . 7 - * 3 And since 1 ng ^ 10 fibers, then a total of 10 fibers will pass through the filter for every 1 g of material impinging upon it. . This is a situation not frequently brought out, but is very significant when exposure levels are monitored in terms of fibers per cubic centimeter. * . Thus the quoting of efficiency in terms of mass efficiency is a "red-herring" statement'that flatters to deceive. It bears no obvious relation to the number of fibers being emitted. ^.owever, based on tests which actually measure the number of fibers .being emitted, it would seem, that both fabric filters and high efficiency wet scrubbers are capable of reducing the . fiber counts to acceptable levels. British experience is that 0 . 2 'f/cc is routine and Johns Manville finds that 1 f/cc is an acceptable value when the results are averaged over a time period`s ' ` ' 1 ' ' IIT R E S EARCH INSTITUTE 46 ` " SPNY 006103 T? .i* : t I s :\ [ [ >i i r i r r I f The medical evidence as to the size of fiber responsible for adverse health effects is not positive nor is the question of whether fibrils of fibers are most hazardous. ' Until the medical questions are fully resolved, it would seem premature to impose inflexible or overly rigid regulations. This has been the view held by the Federal occupational health authorities in assessing their standards, it would seem that thei approach in limiting exposure to that which is possi ble using good modern technology is sensible-.- The same may be said for their monitoring techniques. . ' 10.2 Water Pollution / . ' / * Recycling of waste water is possible and is practiced in certain segments of the industry^ The question of the damage done to streams*, rivers, and lpkes by indiscriminant dumping of asbestos containing waste waters needs careful study. One' must remember it is a natural material which will appear in " water in any case. On the other hand, tfaere is evidence that .asbestos particles ingested into the stomach may cause stomach cancer. - - . '. . .. " * ~ - Again, until medical evidence is clear, it would seem sensible to recycle water whenever this pan be accomplished. -a v'<V: HT RESEARCH INSTITUTE . 49 SPNY 006104 ' ASBESTOS AIR POLLUTION RESULTING PROM THE WEAR OF BRAKE LININGS * 1 A . . v V - - . By . ,`- Colin F. Harwood, l4i.D. ABSTRACT , "** ' Asbestos containing brake lini,ngs have been cited as a _ source of ambient air asbestos pollution. This paper reviews the suggestion and an estimate is. presented which indicates that the asbestbs emission from brake linings is significant. The ways in which this emission may be reduced or eliminated - ,, are briefly reviewed. . .. - * IIT. RESEARCH INSTITUTE * 10 West 35th Street Chicago,.Illinois 60616 `0^ \ 117 R E S E A R C H 65 INSTITUTE " SPN Y 006105 ASBESTOS AIR POLLUTION RESULTING FROM THE WEAR OF BRAKE LININGS TMTRODUCTIOH . v ', * ' Recent interest in asbestos and the realization of its health hazard have raised the question of the extent to which people are exposed.to asbestos on a non-occupational basis. Measurements have been made on urban background levels,,and it has been shown that small but definite concentrations are to be found in areas quite remote from any apparent source. " since virtually every motor vehicles carries several pounds of qsbestos contained in its brake linings and since these are worn away to some degree every time'the brakes are applied then it is reasonable to expect that, they could present a significant emission source. This is. especilly acceptable when one considers^, the 100 million or so vehicles on the nations roads. The paper investigates the possible qxtent of such emissions and presents an estimate of the contribution to urban asbestos, concentrations. Possible means' of .reducing such emissions by use of an alternative or. sealing the sys.tem are briefly reviewed. The Extent of' the mission . ' ... .12 The best information available at the- present time ' indicates that the percentage of `asbestos contained in 'the dust normally emitted from, brake linings is of the order of 1%. However, under conditions, of severe breaking, this may rise to 15%. - ; '. ' /. . . The^average brake friction material contains of the order of 50% asb.e,stos, thus an explanation is necessary to account for the discrepancy between the measured and. theoretical values. : . The most likely explanation results*from the known facts with-regard to heatgenerated at friction surfaces. The work of Bowden and TaboJ- has shown that when two surfaces are placed together the contact area is dramatically less than the apparent area. . ` - ..IF R E S E A R C H INSTITUTE ) .. . . 66 t SPNY 006106 A. trr*i This means that very large energy transfer takes place at these, contact points and extremely high temperatures are reached. In th<? case of brake linings, some evidence of these temoerotures has been generated in unpublished work by the T General Motors Company4 . In this; study, a small hole was cut k through a brake shoe and the radiation collected from the ex rt posed <Thoe surface was monitored. The results suggested that under light broking temperatures of the order of 800-900C were fount}, while during heavy braking the temperature reached 1700-1800C. * ' kt . . ` . ' . . , ,~ *' * ' .* ' ' . *..*. ' , 'T The significance of this data jo the present case is that it is known that asbestos decomposes above 5 0 0 to give forsterite (Mg2Si04) , talc (Mg^Si^Oj Q (OH)2) and water vapor. i Acceptance of''the value of (1% of .asbestos emitted allows ' T< an estimate to be made of the effect of this emission on the \ % quality of-the atmosphere.' ... . / / . Estimation of Urban Concentrations of Asbestos From Brakes . r , ' * Assumptions * -s . .. . . . ' r- t ~ / -* . -:U -J ' ' * a. There are approximately.100 million* motor vehicles. b. Motor vehicles have an approximate average weight of 4 lbs of. friction material, when new, of which 50% is asbeptos. . - . c. The average motor vehicle will require replacement of the brakes after three years of use at which . , , . . time they will,have, l o s t .50% of their weight by ' abrasion. .. - ...- - . ' ' " < * *' * .* A ' * *T ' " V ' a. The. dust emitted will'contain 1% of asbestos fibers. o*.. t , e. O.f^the .wear dust, 80% is emitted and 20% is lodged within the svstem. - 1 " : i . * > * e T1`e -AA* claims there ape 109,000,000 licenced vehicles in cluding 90,000,000,passenger vehicles and 19,p00,000 trpeks. Ill RESEARCH INSTITUTE ' 67 SPNY 006107 .' \i l cm I :.i t~.i on 'Die total weight of broke linings in use is ^ ^ 2 0 00" X 4 = 200'000 Tons- - - The quantity worn off these linings per year follows from the assumptions made in c. as 200,000 x ~ x = 200^000 Tons/yr> This wear dust contains 1% asbestos, hence emission is . ^ QP~ x ^ Tons/yr. Allowing for the fact .that 20% is not emitted, the total emi'ssion is thus } 2000 80 1600 100 -- = 270 Tons/yr. Effect on the Atmosphere There are no facts relating directly to asbestos on ~ which one may judge the effect of these emissions on urban air. However, there has been a considerable ampunt of study done on the diffusion of other materials from automobiles, particularly lead and carbon monoxide. At a recent ACS Symposium in Minneapolis evidence was presented which placed the level for lead emission at 0.01 pg/m in Thule, Alaska and 2.5 |ig/m in Hew York City. Next to busy highways a level in excess of 60 |ig/m may well be possible.' In the light of this data the value of 2 jig/m for average urban air conditions, suggested by GM , seems eminently reasonable. Considering that 1.2j x 10 tons of lead are emitted in total from automobiles then the following factor is used. Avg. Cone, asbestos in^city air from automobiles . Quantity of 2 .|iq/m~ city air asbestos emitted x . , 1.25 x 10 tons Pb from cars Applying this figure to the present case and a'ssuming that 200 tons are emitted ir) city areas, then we get that: UT KtSLARCH INSTIIUTC 68 SPN Y 006108 The avg. cone. 200 x 5 * 1.25 x 105 A 3.2 x 10"3 ^g/m3 or lih . 3.2 x ng/ra3 A similar result is obtained using the dispersion factor for carbon monoxide. However, the values for lead are preferred since it is a particulate emission rather than a gas. The Significance of T h is Value * The question of whether asbestos containing brake linings constitute a significant source of ambient air background, asbestos levels can now'be considered. - Firstly, it is pertinent to review the available evidence , on asbestos levels in ambient air.' Perhaps the most up-to-date information is reported in a recent paper by Thompson and 7 Morgan of the EPA . Their data suggests that values 0.5-15 - . 3 . / *5 * ng/m are appropriate to urban sites, while 0.1 ng/m is to be found in nonurban sites. They give a figure of 0.01 ng/m3 for remote sites. * The California State Health Department in collaboration with the School of Public Health, Berkeley, California, have tested ambient air for asbestos. Their results suggest values of 0.06 source. Nicholson ng/m3 in remote sites and 3 ng/m3 * < Q and Rohl of the Mt. Sinai School near a # * of Medicine have also been active in the .measurement of asbestos in urban ambient air. The analysis of a large number of samples has revealed that 33% of the samples contained 0-0.9 ng/m3, 55% contained 1.0-5.0 ng/m and 10% contained 5-20 ng/m3 and a few Were in excess of this. - ? * . <"^ie workers have been at pains to point out that ` tho results are to be considered preliminary. Thu? they should be regarded not as final definite figures, but rather as good, 11T R E S E A R C H I N S T I T U T E 69 SPNY 006109 considered, preliminary findings. The similarity of the figures reported by the various workers does suggest that at least an order of magnitude has been established. r Consider now the estimate of 3.2 ng/m"5 calculated pre- " viousiy as the contribution from asbestos brake linings. Firstly, it should be stated that this figure is a conservative estimate and allowance has been made for the many factors which could re duce this figure. Secondly, although there is no reason to doubt the factor for the diffusion of lead, it should be realized that this figure is an average value for the whole of the city air. Consequently, much higher concentrations are to be expected in certain areas of high brake usage. For example, near inter sections, tollbooths, etc. In the light of the evidence here presented, one must conclude that asbestos emitted from brake linings may be a major contributing factor in the overall ambient air concen-- tration. ~ .. Further work is necessary to establish more definitely the major contributors to urban asbestos concentration levels. It is not possible to state with assurance how much these - low concentrations of asbestos constitute' a.threat to the health of the general public. Medical evidence and opinion is widely divergent on this issue. However, asbestos, has been rated as a hazardous substance by the EPA and as such it should be*treated with due respect. Emissions should be reduced or curbed wherever this' is possible. To .this end it is worth briefly reviewing how this may be achieved. -rf-xil-;9j^Qgy OF ELIMINATING EMISSIONS The/emission of asbestos to the atmosphere from asbestos ^ ntaining brakes could be prevented in two ways: its use could be ' ^ together, or, the brakes could be sealed. In the * ` r.ior case, * an alternate .would .have .to be found. Ill RESEARCH INSTITUTE r: 70 ' '' SPN Y 006110 Al f.ernati ves to Asbestos For a replacement to be as suitable as. asbestos, have to fulfill a list of desirable features as: ' it would * o Resist high temperatures without degradation or loss of frictional properties. o Combine excellent friction characteristics without severe abrasion. o Provide great strength - asbestos fibers have a greater tensile strength than steel and yet are more flexible. ` " } Have relative economy. Of the materials which have been considered, sintered metal with ceramics and fiberglass have been the most likely candi dates thus far. . ' Sintered Metal - This material has been used and indeed - has the desirable quality of being fade-free, for this reason it is still used in some racing cars. Hoyever, it h as several dis advantages. It tends to be noisy and brake screetch is a problem. They suffer from what is known1 in the trade as "morning sickness", this means that the first stop is very severe, or, . that the cold friction is high. Wear is higher than with asbestos and thus the brakes have to be ,replaced more frequently. R<*eplacing the brakes is more difficult sincie all brakes are honed to fit the drum. Honing metal is more difficult than asbestos friction material. ' ^ . Ceramic Metal (Cermets) - A sintered metal and ceramic composition has been developed and tried. Its use at this time seems to be restricted to the clutches on heavy-duty vehicles (tractors, etc.); in these cases it is usual to use . buttons of the material rather than'a complete annulus. ,, Although "'to a lesser degree, it suffers from the same complaints as sintered metal with respect to noise, wear and severe first stop, and in addition, it is relatively expensive. However, IIT. R E S E A R C H I N S T I T U T E 71 SPN Y 006111 its anti-fade characteristics have l e d :to extensiv^ testing For example, the Ford Motor Company put inserts of ceramic metal at the position of maximum brake wear on their 1958 - f Thunderbird. The concept was abandoned, reportedly duetto uneven braking leading to a directional pull when braking. Fiberglass - Attempts to use fiberglass instead of asbestos have been attempted since 1938. So far, no design has met the exacting standards required. As with the.other materials, the first stop is harsh. Apparently the design is better for disc brakes than drums. A problem is the sensitivity of the brake to moisture. / . Owens-Corning are undertaking development research in this area. They are very guarded with regard to the status of t h e m work, but state that they are actively engaged in developing a product. To date, no vehicles are known to employ fiberglass m their brake friction product. . -Y Sealed Systems t Sealed systems have been seriously considered. Normally c a rely on air cooling and the movement of air round the - per1 l y the m ti0n f the <=" with'high in a limia! mre Clln9 is required. This is achieved s manner by fabricating a superstructure which filte S ^ 31r 3nd dlrects it: inside the brake drum. If a " ' substantial ' n the GXltin* sid^ this would cause a 1 reduction in emissions. cooi t h ^ r r aesign wwch has been used is completely siai r r , ^ T to > problem^ area w ^ TM en'isFion are Possible. ;:ir r r , r . - -blems.aue to overheating ^ The one - .' ` 4 * IT R E S E A R C H INSTITUTE 72 SPN Y 006112