Document oDpovvLqo5yMaeMGjK0e2j2YE

TO, Members of Asbestos Study ConmiHee SUaJECT:Asbestos Fibers Emissions - Friotion Uaterials A seminar was held at the Illinois IMtitute of Tecivlelogy Research Insti~ 'lute baok i" Fopdl of this yaar. Dr. Colin i-01lrwooodf llTRI w.IISone ef the aOvisors 'Ie the tllinois Pollutien Control Soard who was in faver of the proposed 1971 regulations as wriHe ......t.hat is tc iflClude a ban en the# un o-f as.bestes in the brake lining of vehicles ll'Illfl<,lfaeturedafter January 1, 1975 and sold for U$e in Illinois." The pages frc>rllthe I!TAt papar are: pages 22, 25, 26, 27, 28, 1.1>, 49, 65, 66, 67, 68, 69, 70, 71, 72, 73. Your Chairman, Mr. t. H. W6a~r, sant this data 'Ie me fer distributien to the Colm\!Hee. fie comnented On the ~er: "The main issue! would have with Dr. harwood's conclusien would have 'Ie do with whather er not the free fibers or fibrils te'.ased from frictie" matarial decemoosition are truly hazardous i" eny way. and 1 also believe he te"ds 'Ie underestimate the problems in non-asbeSlos ceniaini"g braking systems." Yeur Chairman beliaves that II meeting ef the ConmiHee should be called. I'm IHlking fer a reply On the attaehed ferm., for which ~ !l.lrl .b .all i! meeii"p. From this I will t~y to IIrri~e at a meeting date (perhaps late JUly or late ....g. ust). . E. \'I. Drislane Executive Seeretary --pc:''tfSl. OC25 PLAINTIFF'S j EXHIBIT , :!YY3!!ill!l WV-06017 TO: Fdctlof'l Material!; Ste.ndarels Instituta, 1:_210 Route Ii, Parlllll.l5. N. J. 07652 Inc. GenUemal'" Concerning a prcpcsed meeting of the Asbeato$Study Co"l'llIHe-e, Pl..E~S; DO NOT SCH;wt.E IT rCA THE fOLLOWING 'BEF.J<S: ....ly 24-28 August 7-11 August 1","18 """" 21_25 l<ugust 28-31 Additlcnal Cotmtet>ts: _ c,,,,,.,B,, y,------- _ c.,., _ -.. .. ..., ,,<,~.:- ,, ,".,'~' "''""" ' ;,:. "" June 1, 1972 l:r. t. W. Drislane, E,:(e<;:utive Secret.a..-;!' Friction ~.ateria:Ls Standards Im.titute, Inc ~rgen ~~ Offiee Center, .210 Rouu II. ?ar=..s, K.J. 07652 Lear Ed: The a.ttached lIl<lterial concerning autoootino eminions of UDestos fibre "'"as received from Illinois- Im.titute of Tecnnologv Resea..-<;:hInstitut.e Y"'st.erday an:! pro"gal:tly will be of .interest. to other llIlilmi:>erli of the f'!GI ASDell':.OSSw:!y Commit.tee. 1 suggest t.hat you cir'0m4te it to them. ':1"';"sll'.a.t!!r-';" 'WaSfOl"'l!1!.Tdebdy- !Jr. COlli F. Harwood-o~!I'I'Rl as a S\;?pJ.!!::Ie:'lt<: ir.!::r:;;ation presented at & selllina: on a:"oest.Qs- th!!y eencu<;::'edApril L t.hrough 7. Very little at:t.ention "''ll-S devoted to allUl:llOtive ell!issior. ecw-eee dl.:rinS t?e seminll.r. The l:2lill issue 1 wculd have ",<itb. Dr. Haf'wc>od's conclul'don "Ow.d have to do lo1.th wether ot' nat tht: free fib:'es es- fi'QrUl! rf!leased froOll f ...ietion J::atf!"':j.a1d. ecolllpositiop are t::"l<ly ::a:n.rdolls in a.ny way, and 1 ;;.150 belieVf! he tends to \lllderellti:late the problems involYed in non- asbestos eonta.ining brakinG s,.stems. Sines it appears lUU'll!cessuy and }It'Qbab1s iJ:Il?::'l!sibll! to schedule an Asbestos Study Co"lllli.ttel! meetin!> in June and I "l'W. be awar the !it'st t'I<Qweei'_~in J-u.l:y, 1 think it miiht be p:nldent to tentatively schedule '...-roI'<lli':l! :la"t1lr. July, ,prtlfe:-,wl-y--dlU"ing tM 14st,-x... .By ,tilai;,.t.1llle ;;: ~eet there will be a m1llli>er of lNbjects wcTtm.ilile review'.r.e;. "It pI< agree, ltincl1y ea.nV&I!lt!he other lllelIlbers and pick a date. As fil%' as 1 kno'o<, 1 will ee available: lU)t:ime durin!> tbe week of Jll1"v 2.l... 1 am abo open eee _ek a!tll'T that in t.he event this- suita the at.non-s- better. Best TegarodS-, (I<';: ,1. H. WI!&ver at~achments such that the dust created is arrested at the sourc; and collected in filter bags. Commercial deVices are availa:le but normally firms ~th a sincere interest in pollution control, design a'nd fabricate their own devices. TWQ. ,examples of s*uch .. devfeee are shoWl'iln Figures 6 and 1. These control hoods werl: on the high veloeity, low volume principle and can be readily adapted to industrial vacuum cleal)er s)sterns. Whenarrest-at_the_source systems are not possible, tecn_ niques silnilar to those employed by the asbestos spraying industry IT.aybe utilized. .Rules WhlChrelate more specifically to tabrication of asbestos products may be found :tn such pUbli_ cations as: 1.. "RecommendedPractices for Fabrieating, Handling and Construction Industries." Health and Safety Council_Asbestos Cement Products Association. 2. "RecommendedEealth Safety Practices for Handling and Applying Tnermal Insulation Products Containing Asbestos," National Insulation ~janUfaeturers . Association (NIMA). 3. The Asbestos Research Council _ Control and Safety Guides (London, England). 4. "Recommendations for Handling AsbelltOS," Engineering Equipment Users Association (EEUA) , E.E.U.A. Eand_ hook NO, 33. 3.3.3 Friction Material A~~lications Typical friction materials contain 30 to 50% asbestos and may .. be .up J;..c .7.o-".aru:S; -t:hetnd_t:t'"J -t'h<l't"ll'llmU'factu1:'E!'st:hmesae-, terials is ranked third (1969) in the consumption of asbestos fibers. Crys01;ile is the preferred variety because it has better frictional properties than amph.i:bolasbeStos and does not exert so much wear on the opposing surface. The major uses of asbestos_containing friction materials inclUde brllke linings, brllke discs and clutch facings. These products have been applied to a Wide variety of industrial commercilll products. and nr RESEARCH INSTITUTE _sources of :mission _ EmJ,.$sionof asbestos f rcm frietlo:; m<lte:;ials results from normal day_tO_day usage. A.I:I idea of the scope of this source can be gained from the estimation that_ the average automobile wears out 3 to 4 sets of ~ake linings, aDd ~ 1 to Z sets of s.lutch facings during its lifetime. and that commercial public transport vehicles wear out many more sets. Pata concernin9 motor vehicle 'brake linings for the ..'.hole of the United States are given in the following: Vehicle miles during 19:66 Mileage life of brake linings 1,010,000,000,000 27, so.c arake lining sets on new vehicles 10.718,000 Pounds of asbestos per set of bra'ke linings 3 '!'ests performed on brake linings have indicated that under conditions of no~l usage, considerable alteration of the asbestos oceur~. It is reported that most of-the dust collected from brake drWlls appears non-fibrous and is s.l.ll'Iilar in appearance to thermally degraded _asbestos, The sU9gestion is that h.l.9h temperatures at the brake lining/drum contact points actually reach degradation levels. Tests on brake linings, brake discs and clutches have demonstr~tee that the quantity of fiber emitted is some function of the severity of the braking conditions (see Table 3) , HQW- ever. even at'the level of 1%, the totalell'lissions must be 1 conSiderable Whenthe total tonnage in use is considered. Furt;;her. the emissions are 'lik",~y to cccuz- at p"laees 0'1"'hi<jh j density population and restricted ventilation. That is, in busy main streets of towns surrounded by large buildings. j The effect of different braking conditions and different types of friction materials on asbestos ell'lissions is the sUbject 1 of a stuel:ybeing sponsored by the Environmental Protection Agency. i other studies are being conducted in California and some work on roadsides has been done at Mt. Sinai. NewYork. The PA 1 study will estaJ::,lish the extent and nature of the askest.os III RESEAlq:t\ IIUTITUTE J -._. , Tal::J.e A(STBeEsStTORS esEuMlItsSSIbOyNSEleFcRtOrMonBRMAiKcEroLgIrNaIpNhG)S , 1',."",,"'t L Allt","oblle <:1,.11,b"nk"s "" "" "" " ,", " 1I1"nnd , , c c n ,French 'tnt ~h2L :rdeUon Frietlon Frietion Fr1etictl Friction Fr1<:tion "No. S"'ltIh~~ 6 , s 1 s , Condtt!OM nf T,,'tr 300~llOO 2SO_800 300.700 700-900 :;00-800 300700 I'n'8enee of I'rN' rll:>..... ". "4 FTee rIb ...... <1 ..><0,. c , <1 tl....erou. _10 ,~ " ". <I 1. " F Friction s 300.800 ". <I Ce,.,..n ," c l'rJeth>n l00-S00 F~ <I , " c, " Fried"" I 600-700 llumerOIlJ _IS J " " ,~10, " Frieden a 100-600 <I 11, A"t""""bib J Dynlllll""''' t l!r I normal None c <::l uteh 1 , "." 11, 1111e""'" b i h ,,, <:I1$k b .. ak" Dyn" .. " .... te:r I dl'ivinl normal driving <' 13, BIl= dl""'" L Oyna.. QftI"ter I eity None o brake 1, ,,", " ,~IS, Truck d",," r 1 bnke (tight) Friction Friede" drivint a 450-550 NOM: 10 300-800 <I 1 ~W"Ir,ht estimated f .."", fibe" volume. 1, , i ,. emitted from brake drums, 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 Techniaues .. Emission at over"haul _ To avoid blowing t"he aocumulated 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 suet:ion. Of the devices tried, a simple hand_held vacuum cleaner has proven to be the mest flexible unit. Changes to the original design have been limited to the addition of a disposable paper bag inserted in the original doth bag. The paper bag may be easily sealed. before removal to prevent emission. SUbstitution - Beyond the adaptation of better cleaning practices during brake and clutch maintenance. as mentioned above, additional controls seem to be limited to improve de:,;ign of brake and clutch assemblies and/or $Ubstitution of other materials for asbes~s. The high temperature properties and exceptional tensile strength of asbestos have resulted in very compact and economi_ cal desi~n. These same unique properties 'Which make asbestos applicable to friction materials also make the application of substitute materialS very difficult. The tens~le stren~th and modules of rigidity of asbestos as compared to several candidate sUbstitute materials follows, Tensile Strength lWin.2 Asbestos 550,000 Fiber yerns 180.000 Steel wool 50,000 Mineral wool 25,000 Modulus of Rigiditv 30,000,000 3,000,000 100,000 60,000 lb/in.2 There is no doubt that SUbstitution of other materials for aSbestos is possible, but the design changes required to accommodate the stresses and temperatures involved 'WOuld result in lIT RESEARCH INSTITUTE 27 larger. more e~pens~ve components. arakes - The recent adoption of disc brakes by the auto_ motive industry 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 anyone 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 matet"ials 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 Il"::!ivoefntthe automatic trllnSlllissioannd the t"edesignof manual clutch friction surface. The clutCh surface of the automatic transmission is im_ mersed in an oil bath which Virtually ~lilninates airborne pollutants. Further. the COOling affect of the oil bath reduces the requirement for high-temperature capability materials. Automatic transmiSsion clutCh facings may be mace from either s;nterec metals or fibrous cellulose materials. Many manual clutches have redesigned friction surfaces Whicn consist of numerous small circular pads or diacs attached to the clutch face as Opposed to the standard annular ring friction surface. These small pads act in the same manner as the disc brllkes friction pad. 'rhus. lower stresses and oper_ ating temperatures associated with ,the new design reduce the need for aSbestos-containing frietion materials. tIT RESEARCH tNSTtTUTE 2. ----------------------------------- I -- 10. ,01 Emission Levels I In understanding control techniques and their effieiencies, it-is illlportant not to be confused With effieieneies quoted"on ,.. I ill "'eight hasis ~nd_those basea on Ii partiele count basis. Firstly, considering efficiency based on ill weight basis, J it is relatively easy to get ill very high effieiency with particles whose size is in excess of S~ with ill variety of control 1 devices (see Figure 10). However, the efficiency dees drop off considerably with decrease of particle size, for example, see J Figure 11 tor 1u particles. (It s1'l.ou.ldbe noted that these graphs refer to spherical particles _ information on fibrous particles is not presently available.) 1 Nowconsider what these apparent high efficiencies mean 1 in terms of numl:>erosf fibers. It can be assumed that 103 average fibers of asbestos weigh approximately 1 nq , 1 If 1 9 of asbestos material approaches a filter rateo at ,- ,even as high as 99.S9S% efficiency. then the quantity passing 1 :~::;:~ :~~~ ~t~~~~O~~ ~~70:i~rSn~11~;:s:i~~;0~g:9t~l~ilter for every 1 g 0' material impinging upon it. 1 This is a situation not frequently brought out. but is very significant w.henexposure levels are monitored in terms of 1 fibers per cubic eentimeter, 'Thust'he quoting of efficiency in terma of mass effie1enc)' 1 is a ~red_herring~ statement that flatters to deceive. It eeaee no obvious relation to the numberof fibers being emitted. 1 However.besed on tests which actually measure the number of fibers bein<;lemitted. it would seem that beth fabric filters I and higb efficiency wet scrUbbers a:re capable of redueing the fiber counts to aceeptable levels. British experience is that I 0.2 flee is routine and Johns Manville finds that 1 flcc is liln aeeeptlilbleverue whenthe results ar-e averaged over a time par:i.od. ut RESEARCH INSTITUTE The med~al evidence as to the size of fiber responsible for adverse health effects is not positive nor is the question ofwhether fibrils of fibers are most hazardous. Ontil the - medical questions are fU11y resolved. it wourd 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 possible 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 practic'ed in certa.insegments of the industry. The question of the damage aone to streams; rivers. and lakes 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, there is evadence that aSbestos particles ingested into the stomaeh may cause stomach cancer. Again. until.medical eVidence is clear. it would seem sensible to recycle water whenever this can be accomplished. I ! I I I IlT RESEARCH INSTitUTE 49 ASBESTOS AIR POLLUTION RESULTING FROM THE WEAR OF BRAKE LININGS By colin F. Harwoo~. Ph.D. ABSTRACT Asb~stos containing brake linings have been cited as a source of ambient air asbestoS pollution. This paper reviews the suggestion and an estimate is pre~ented vhich indicates that the asbestos emission from brake linings is significant. The ways in which this etnission may be reduced or eliminate~ are briefly reviewee. lIT RESEARCH INSTITUTE 10 West 35th Street Chicago, Illinois 60616 111 RstARCH IHSTllUTf ASBESTOS AIR POLLUTION REStJ1.'tING FROM niE WEAR OF BRAKE L1NINGS INTRODUCTION Recent interest in asbestos and the reali2ation 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 bean shown that small but definite concentrations are to be found in areas quite remote from any app<lrent source. Since virtually every motor vehiCles carries several pounds of asbestos contained in itsbrake linings and since thes~ 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 especially acceptable when one considers the 100 million or so vehicles on the nations roads. The paper investigates the possible extent of such emissions and presents an estima,te of the cont'ribution to urban asbestos concentrations. Possible means of reducing such emissions by use of an alternative or sealing the system are briefly reViewed. The Extent of the emission The best information available at the present timel.2 indicates that the percentage. of asbestos contained in the dust normally emitted from brake 1iniQqs is of the order of 1%. However. under conditions of severe breaking, this may rise to 15%. The average brake friotion material contains of the order of 50% asbestos, thus an explanation-is necessary to account for the discrepancy blitween the measured' and theoretical values. The most likely explanation results from the known facts with regard to heat generated at friction surfaces. The work of Bowden J and Tabor has shown that when two surfaces are placed together the contact area is dramatically less than the apparent area. ur RSr,o,RCH INSTITUTE " -------------------_ .. ------------------------------- Th~~ mebr.S~r~~ very large energy trar~fer takes place at thes, contact points and extremely high temperatures are reachec. In thecese of brake linings, some eVidence of these temp(!.':ll:ures has been generated in unpUblished. work by the Cener~l Motors C~pany4 In this study, a small hole was cut through a brake shoe and the radiation collected from the exposed shoe surface was monitored. The results suggested that under light br~king temperatures of the order of 800_900C were found, while during heavy braking the temperature reached 1700_1flOOC. The significance of thiS data to the present case is that it is known that 3sbestos decomposes above 500C5 to give forsterite (Mg2Si04), tale (Mg;;Si40l0(OHj2) and 'Water vapor. Acceptance of the value of 1% of asbestos emitted allows an estimate to be made of the effect of this emi.ssion on the quality of the atmosphere. Estimation of Orb~n Concentratia~s from arexes Assumntions af Asbestos' 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 aSbestos. c. The average motor vehicle will reqUire replacement of the brakes after three years of use at which 'ti:me1:'hey '"Wi'l:!. "'I-rav1e:Q'S't "$'0""" "o'f "their weigh';;by abrasion. d. The dust emitted will contain 1% of asbestos fibers. e. Of the wear dust. 80% is emitted and 20% is lodged within the system. -The AAA claims there are 109,000,000 licenced vehicles in_ cluding 90,000,000 passenger vehicles and 19,000.000 trucks. III lHSEARCH m s rrtvr r 67 -------- ----- Coleul"tiO/'l The toto1 weight of brake linings in use is 100,000,900 x 4 '" 200.000 Tons. 2000 The quantity worn off these linings per year follOWS from the assumptions made in c. as 200.000 ~~-~13 ~ .1.~.0..0....."" 200,6000 !'ons/yr. 'l'his wear dust contains 1% asbestos, hence e~i5~ion is 200,e0, 00 x rO1O '" 20600 Tons/,}r. Allowing for the fact ,that 20% is not emitted. the total emission is thus 2000 6 x 80 100 1600 "" 6 '" 270 Tonsjyr. Effect on the Atmosohere There are no facts relating directly to asbestos on which one may judge the effect of these emissions on urban air. llowever( there has been a considerable amount of study done on the diffusion of other materials from automobiles, particularly lead and carbon monoxide. At a recent AC$ SymposiUl'll in Minnenpoliso evidence was presented whico placed toe level for lead emission at 0.01 f!g/m3 in Thule, Alaska and 2.5 J~g/m3 in New York City. Ne~t to busy highways a level in excesS of , ,SO I,g/m may w~l be . possibl~. In the light of this data the ,value of 2 l,g/m for average urban air conditions, suggested hy.G.'l , ,s_S.emi.nelltl;- .r-..e<ilSCnl:a"J.:c)olnes.j derilll;lt..ha.t 1.25 ~ 10 S tons of lead are emitted in total from automobiles then the followi~g factor is 'used. I Avg. Cone. asbestos Quantity of :2 Hg/m3 city air t in eity air from automobile:s asbestos emitted x 1.25 x lOS tons Pb from carl> Applying this figure to the present case and assuming that I 200 tons are emitted in city areas, then we get toat: III ReSEARCH m s rrrur c I ':l':e i!v;:. ecec . :::R: ~ -0< ~ ,200 5 1.25 x 10' '.2 x 10-3 a I-'g/l'l\ '.2 x n9/m3 A similar result is obtained using the Qispersion factor for carbon monox~de. However, the values for lead are preferre: since it is a particulate emission rather than a gas. The Sionificance of This 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 a:nbient air. Perhaps the most up_ta-eate infantlation is reported in a recent paper by Thompson and Morgan of the EPA'. Their data suggests that values 0.5_15 ng/m3 are appropriate to urb~n sites, while 0.1 ng/m3 is to be found in nonurban s~tes. They give a figure of 0.01 ng/m3 for remote sites. The California State Health Department in collaboration with the School ~f Publ~c Health, Berkeley, cer.xeceni e , have tested ambient air for asbestos. Their resUlts suggest values of 0.06 ng/m3 in remote sites and 3 ng/m3 near a source. NichOlson and I".::a>holf the Mt.. Sinai SChool of MeQicine trave-aj-sobeen aee.ave in ,t:nmeeeeur emerrt;o'f asbest.os in ur'oan arr,bientair. The analysis a,f a large number of samples has eeveeree that 33% of the samples contained 0_0.9 n9/m3, 55,," COntained 1.0_5.0 ng/m3 and 10"" contained 5_20 ng/m3 and a few were in excess of' this. All of the workers have been at pains to point out that the reSUlts are to be COnsidered preliminary. Thus they should be regarded not as final definite figures, but rather as good. III UHA.CH IIUflTUtE " _._-----...-c- considered, preliminary findings. The s~ilariey of the t;.gures reported Oy the various worXers does suggest that at least an order of magnitude has been established. Consider now the estimate of 3.2 l'lg/am calCulated pre_ viously as the contribution from asbestOs brake linings. Firstly. it should be stated that this figure is a cons~rvative estimate and allowance has been made for the many factors which could re_ ecee this figure_ Secondly, altho1l9h there is no reason to dou!:>t the factor-for the cifusion of lead, it should be realized that this fi9ure 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, toll,.booths, 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 ccncentration. Further wor~ is neeessery to est~bli~h 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 ha~ardous substance by the EPA an~ 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 achieyed. 'l"CntlOLOO'f OF ELI1".U~A'1'rNG EMISSIONS The emission of asbestos to the ~tmosphere from asbestos COnta1nin9 brakes could be prevented in two ways: its use could be b4nncd altogether. or. the brakes could be seeaee :tn the fQrmer case, an alternate would have to be found. lit UnAtCIi ltUTHUf! 70 ------------ ------------------------------------------------------ -------------------------------- Alter-natives to Asbestos Fo~ a replacement to be as suitable as asbestos, it would have to fulfill a list of desirable features as: Resist high temperatures without degradation or loss of frictional propert~es. Combine e~cellent friction characteristics without severe abrasion. 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. sinter-ed metal with cerareics and fiberglass have been the most likely candi_ eaces thus far. Sinter-ad 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. Howeyer, it has several di~advantages. It tends to be noisy and brake sereetch is a problem. They suffer from what is Known- in the trade as "llIorning 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. Replacing the brakes is more difficult since all brakes ace honed to fit the drum. Honing metal is more difficult than asbestos friction material. Ceramic Metal. (Cermets) _.A sintered metal and ceramic cOlllposit:.iohnas 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 Duttons of the material rather than a complete annulus .- Althou.gh to a lesser degree, if"suffers frOlllthe same complaints as s1ntered metal With respect to noise, ~ear and severe first atop, and in addition, it is relatively expensive. However, liT RESEARCH INSTITUTE 71  its anti~fade'characteristics have led'to extensive testing. For ex~np~e. the Ford Motor Company put inserts of ceramic met'al at the post ticn of maxi.mu._lb'ar.ake wear on their 1958' Thunderbird. The eoncept was abandonea. reportec:11y Que to uneven 'braking leading to a Clireetional pull when"In'aking. ~ Fiberglu!! _ Attempts to use fiber91as~ instead of asbestos have been attemptea sinee 19)8. SO far. no design has met the exaeting standards re~~ired. As ftith the other maeedaJ..s.the first st.op is harsh. Apparently the design is better for disc brakes than drums. A problem is the sensitivity of the 'brake to moisture. Dwens_Corning are undertaking' development, research .in this area. They are very guarded with regard to the status of their work. but state that they are actively engageQ in developing a product. '1'0date, no vehicles are known to employ fibe:rglass in their brake friction product. Sealed SYstems Sealed systems have been seriously conSidered. Normally. cars rely on air cooling and the movementof air round the brall.e caused by, t:he motion of the car. However-with high performance cars. more cooling is required. This is achieved in a simple manner by fabricating II superstructure Which scoops up air and directs i~ inside the brake drum. If a filter were added on the exiting side. this would eause a substantial reduction in emissions. A more elaborate design'which has been used is to liquid <:001the, br>akesystem. This enab!e$ the braking system to be completely sealed and thus no emis.!'ion are possible. 'the one problem area with this' deSign 1$ that the oil seals must be extremely re1.iable. However. with a well designed system prOblemsdue to overheating eecre be 1.argely eliminated. ur RESEARCH INSTITUTE 72 CONCLUSIONS An estimate has been made of the asbestos concentrations to be found in urban air resulting from the use of asbestos , concaining brake materials. The results indicate that brake use may well constitute a major source of asbeseos background levels. The quantity in comparison to occupational levels is extremely low. A time weighted average occupational ex~ posure level of 5 flee would be of the order of 100,000 times greater than a background level of 3.0 ng/m3 The medical sig'nificance of these results is not known with any certain,cy" At the present time, no alternative to asbestos coneain~ ing friecio[l-l'roduccs is developed to the stage of finesse required by the i[ldustry. It is difficult to believe'that modern technology cannot overcome the problems presented by the use of alternates. The use of sealed brake units is a second possibilitY. Again there do not seem to be any ins,urmountable techno1ogi~ cal problems, but no info:t'lllacion is available all to the ccs t and time factors , u't RESEAlI.CK INSTITUTE 73