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Ponearch S Development Cent or fay 22, 1973 i ' (^ ^ \ ASLESTOR-EMISSIONS FRO" BRAKE DYNAMOMETER TESTS A. E. Anderson, R. L. Coaler, R. C. McCano anti J. W. Spys, Scientific Research Staff, Ford Motor Company. (Presented at the.3973 SAE' National AutomobiIt* Engineering Meeting, Detroit, May If-, 1973) , SUMMARY by J..W. Axelson Dynamometer tests were made with a production disc: brake and all airborne wear pnrticJcs were collected on 0.45 um filters. Asbestos fibers were detected and measured by the use" of transmission electron microscopy at 40,000X and positive .identi fication was made by electron diffraction. Mont of the lining asbestos (99.95 percent) was found to be converted to a nonfibrous material by the high f]ar,H temperatures of the braking surface. Brake flash temperatures as high as 98 OC have been observed on a test machine. They estimate'.that about 28,000 tons of asbestos are used each year by the friction materials industry in the U.S. (J-M estimates about 45,000 tons). Bess than half of* til is,' or 12,000 tons, is estimated, to wear away. Throughout the paper they use a safety factor of JO to make sure they are stating maximum quantities. I'or instance, they found that only 0.002'3 percent of the lining wear was released as asbestos fibers, but state this figure as less than 0.02 percent. Likewise, the concentration of asbestos fibers in tli*' atmosphere from brake usage was calculated as 0.007 x , ' 1Q"9 gms per cu meter1' but was reported as 10 times that or 0,07 x 10"5 gins per cu meter. Rome, of the pertiinent. data are given in the following table. These are actual values without multiplying by the factor of 10 as they did in the paper. Background asbestos in ambient test air "Asbestos, fiber from brake m exhaust air Tora3 asbestos fiber in exhaust air EsIimi nted brake asbes tos in urban air* Asbestos fiber from brake in airborn wear dust Asbestos fibci released from lining wear 1.9 x 10"9 g/m3 1.3 x 10~9 g/n3 3.2 x 10"9 tt/m3 0.007 x 10-`J g/m'l 0.005 percent 0.0023 percent ^Extrapolated "from data on residence time for lead particles. t SCF-FORD-1062 s\ 'May. 22/ 197 3 ' J' iJj'O 2 ' \ Asbestos Emissions from Brake Dynamometer Tests ti Local Detroit atmospheric concentration ranges from 0.5 to 13.-Vx 10*"5 qms per mi motor so the calculated value of 0.00(7 x 10-5 gms per ci}, meter is only a minor fraction of normal conditions accruing from all sources i no Dueling ^natural weathering of* ashestos-bqar.ing rock and soil, mining, farming andexcavating. This leads to their final conclusion "Based on this up_ _per bound, the use of brakes was judged to be not significant ns a source of atmospheric asbestos". cc: i ) J. .E. M. Hutcheson - Asbestos N. W. Hendry - 3 West i H../G. Donovan ~ 3 West *15. M. Fenner 4 North ' F. J . Solon, - 1 West' W. C. streib - R&D Ctr S, Speil - BSD Ctr i t f J A t 1 1 J ' ASBESTOS EMir; 10.73 FROM BRAKS DYNAMOMETER TESTS .' i>y , '' \' A.,E. Anderson, R. L. Gealer, R. C. McCune, J. W. Sprys Scientiific Research Staff, Ford Motor Company, P1 Dearborn, Michigan 48121. i I asbestos hmtss tins from brake . DmftMOtoETgR TESTS ., by '' . A. E, ^Anderson, R, L. Sealer, R. C. McCune, J. W. Sprys 1 ' , Scientific Research Staff, Foret'Motor Company, Dearborn, Michi "an ` i . 1s8l?l i* ABSTRACT . Dynamometer tests of. a production disc brake provided new information on asbestos fiber emissions during breakin, normal use, and high temperature use conditions. Both anbient air and brake cooling air wore sampled isokinetically, using 0.1+5 filters. Examine!ion of test and background filters required a clarification process to maximize fiber detectability, the use of transmission electron microscopy (at 40,000 X) for detection, and electron diffraction for positive identification of asbestos fibers.' Most of the lining asbestos was 1' ' .found to be converted to a non-fibrous material by the high flash temperatures of the braking surface. Le,ss thihn 0.02& of the lining wear was released * as asbestos fibers. The/, concentration of asbestos fibers in the urban atmosphe>re, `` < _ due-to brake usage, was conservatively estimated at less than 0.07 x lC~a grains per cubic metey. Based on this upper'bound, the use of brakes was judged to be not significant ss & source of atmospheric asbestos. ' INTRODUCTION Asbestos has he^n. a rancor constituent of automotive friction materials for, more than 50 years. It is.used to impart strength, ^flexibility, i and. heat resistance to a brake lining and to enhance friction and wear proper- ties.i Most present brake linings use resin or rubber binders and chrys'otile asbestos, together with organib and inorganic friction modifiers and fillers. 'The asbestos content varieG with formulation, from s. low of 25$ to about 65$ by weight.. Minimum asbestos levels are found in some high performance European disc brake linings which are highly filled with metals and inorganic constituents, brake linings in the U. S. average about 50S asbestos content. ' (730 Kkr.) Of a total U. .0. annual asbestos consumption of 8CO,000 tons).about (25 Mkg) f 28,000 tons/fof chrysotile asbestos are purchased annually for friction materials , * of all types (l). Of this, it has been calculated that brake lining wear ' (U MkC) consumes about 12,000 tonsil of asbestos per year. Roughly an equal amount * \ remains on brake shoes at the time of replacement or is manufacturing wastage. Recent tests have shown that densely populated urcan atmospheres Often contain significantly `higher asbestos concentrations than surrounding areas (2). Background asbestos levels in the atmosphere result from the r* natural weathering of asbestos-bearing rock and soil, as well as from mining, farming,.and excavating. The generally higher urban concentrations suggest commercial and industAal sources. Brake lining and clutch facing wear was suggested by ibomson (^) as a possible source for higher asbestos levels in the urban atmosphere. ( Lynch (4), in a study undertaken by the Public Health Service, 1 ` reported the findings of several brake dynamometer and friction machine -teet6 in which wear debris was trapped on a filter and subsequently examined by means/of a transmission electron microscope (TEM), He concluded that' "Tree fibers from brnke lining wear seem to be an Inconsequential health factor in urban air pollution." Lynch delected no free fiber from ar^ automobile Clutch.and a bus,'drum brake, but some free fibers were found in one test of an experimental disc brake.' ' ' i ! ' 1 With mounting concern o'/er air quality in general, and asbestos pollution in particular, this`study was initiated in 1970to provide additional lata on, the asbestc3 emissions from disc brakes. OBSERVATIONS OF LINING WEAR The near absence of free p.sbcstcs fiber from lining wear has been 1' I , reported by LuxOn (5) using X-rny diffraction and by Lynch (V) using the TEM (transmission electron microscope). Several authors have suggested that } '' interfauial temperatures during braking could be high enough to decompose . the chrysotile asbestos into non-fibrous thermal degradation products. Ana-' *i lytioal relationships exist which permit calculation of ir.terfaciol tempera- unis (6). However, several of the significant parameters arc difficult to determine accurately for heterogeneous materials such as brake linings. The asbestos crudes (larger fjiber bundles) were calculated to reach their rapid t decomposition temperature during normal braking at speeds above 56 MPH $` (2? m/a) as an upper bound value and above 18 MPH (8 m/ ! J as a lower bound value. An experimental approach v;as undertaken to provide closer bounds. * i Added insight into the thermal decomposition of asbestos fibers in brake lining' wear was ablempted by direct visualization cf tne frictional t process; A Gmail laboratory friction test machine was constructed using a thermal shock resistant (Vyco^) glare rubbing surface (replacing the conventional cant iron) In which the friction interface was directly viewed wi*h a low power (7-50X) binocular microscope (7). Scaled rubbing velocities were ure.i to compensate for '/ *w the thermophysical property differences between the glass and rset iron. -3- ' Moderate scaled velocities, roughly equivalent to 12 MFH (5 m/s ), provided a view of intermittently incandescent asbestos crudes. During the ' ' \' initial burnisliing operation resinous material surrounding these asbestos .i crude^ vas observed to pyrolize, producing microbcoca of condensation ' 'I products around the crude. Th<?wse organic products of resin degradation and , t.ne apparently powdered a,sbestos decomposition products'were seen to smear ' into platelet?, often of such size as to be discernible to the unaided eye. ' ' At higher rubbing velocities {over 30 MEI, or 13 m/6 J the platelets formed a surface char layer under the action of more severe thermal and mechanical action. The larger asbestos crudes then could be seen to glow 1l with1apparent depth and for greater time durations, often several seconds. i . Hie actual brake lining contact area was only a few percent of the total > ' * '' available surface, .with contact spots moving in a random manner with time. Prom these fraction visualization studies it appeared that local flash temperatures and .severe mechanical action could be major factors in the breakdown of asbestos fibers for most brake usage.- Examination of the lining surfaces reverted the presence of non-fibrous magnesium silicate'in both crystalline (Porsserite; and amorphous phases. McgAesiur^ silicate is a thermal degradation product of chrysotile aSbestos.^ Forsterite transformations have been reported to occur at bOOC over a period of hours1. Differential thermal analysis (DTA) studies in our laboratory indicated this transformation occurs within seconds at 620C. ' Special brake lining formulations were then prepared and tested on the glass visualization apparatus ar.d a Friction Assessment and Screening Test (FAST) machine.(8). Chemical reactions were found to take place at the friction interface'Which would require a flash temperniure rise of 7^0"C to initiate when an. equivalent of 31? MPH (l6 m/s) rubbing speed was used on the lt FAST machine. At this same speed melting of inorganic lining additives and ** 1 ' metal particles confirmed brake flash temperatures up to y80"C. .' '' x -Ji.- . *' 'l Based on these findings, it Mould not appear surprising for few asbestos fibers to be emitted from brakes in normal usage, however some . mechanical rer' poval of fiber appeared possible during the first sev\ e'ral brake applications with new linings. Also, high brake temperatures possibly could i1 ' > weaken the organic binders and cause increased fiber emissions. ti JEST PROCEDURES - i Complete sample collection and examination procedures, along with * sample data calculations are included as Appendixes I, II, and III. Briefly, , the bests were performed ns follows; a new Pinto disc broke assembly was installed on a single station brake dynamometer In a room v/hich was cleaned rI ' of extraneous asbestos sources. Air from within the room was blown through a diffuser screen to provide a velocity distribution over the brake which .l ' approximated that .of vehicle usage. The air stream in front of and behind the brake was sampled isokinetic ally, using matched 0.4j lira filters, holders, and air pumps. Note the system schematic in Figure 1 and the actual test- sc-tup * 1 in Figure 2. The brake exhaust sir was discharged out of the building. The first pair of.filters were used during the first 82 burnish .* stops, ;o represent "breakin" conditions. After further burnishing, a second pair of filters collected samples during 560 "normal use" braxe applications. 5 ._ A third set of filtenb then were utilized in a "high temperature use" test of 41 brake stops. ' All brake applications were made from a 40 MFH (lfl m/s) equivalent speed. Breakin and norranl use tests employed brake toremes corresponding to - one-quarter "g" (4,9 m/sp) deceleration. This torque level was doubled for the high temperature tests. During the normal use procedure, the test filter was located for 20 - I *, . brake applications at each of 28 grid locations in the exhaust duct throat, to ' insure a representative-Stapling of the'air flow over the brake. Thl3 test grid  ! ` , \ ' \ and filter may be seen in Figure 3* ^ central collection site in the test grid N was uned for the "brcakirl' test1' and the final "high temperature" test. Samples of the three pairs of filters (breakin, normal line, and high temperature use) were subjected to a clarification process involving low temperature' ashing to oxidize all! organic material and mechanical action to "i i separate the particles. This assures maximum detectability of asbestos fiber (2). \ RESULTS AND DISCUSSION '_ ' Transmission electron microscopy at ^0,000 magnification was used in the search for fibers. At this magnification the ultimate fibrils appear to be above^ one millimeter (O^.Oto inch) in diameter. Quantity, length, and apparent diameter measurements provided data for calculation of asbestos fiber mass per unit of filter area. Couoled with dimension, mass, and flow determinations from .- t" ' the dynamometer tests, this data was used to calculate the emitted asbestos > fiber concentration in the collected wear dust, in the coding air stream, and from the `brake lining worn. The sifce distribution of collected fibers was not determined by this method, since the clarification process involved sufficient ` mechanical action to reduce most fiber bundles to the ultimate fibril size. . Additional jamale,? of the "normal use'1 test filters were examined ' on the ^EM without recourse to the clarification process, in an effort to determine the asbestols fiber size distribution. Roughly 10$ of the asbestos fiber was visible on the background sample, based on the results from corres ponding samples after clarification. The largest observed fiber bundle was 0.20 um in diameter and over 1.1 um long. A similar direct TEM search of the "normal use" test filter revealed about ZNj of the asbestos fibers observed after clarification. This reduced percentage of visible fiber was attriouted to the greater-.concentration of obscuring matter in the test filter. However, the . ,t largest observed,asbestos finer in the test filter (O.13 uf- in diameter and over . 1. 1 i"? urn t 'l wps about; the s.-ittip rti 7P rus was found on the h.-ickpoond snirvnlr. -6- ' The similar, low fiber content of both >% i ekf'round nncl tost filters precluded n fiber size distribution estimate. However, It appeared Unit the quantity of the larger asbestos fibers on the test filter war, no greater than tfyat of the I backgro' und filter..i '' This supports ti he observation from the lining wear visualization tests 'I . that normal brake wear degrades most of the asbestos fibers. A brake lining grade l' \ . of asbestos appears on the TEM as in Figure 4. The fiber bundles ere composed of strong., but weakly adhering fibrils of about 0.05 um (roughly 1 microinch) diaraetc*'. Mechanical action causes the larger fibers to "open" into smaller fibers or even fibrils, as illustrated in Figure 5* Contrast these "raw material" fibers V>ith one of the larger fibers (Figure 6) and one of the more typical fibrils (Figure 7) from the "normal use" test filter. The similar, low fiber content of both background end test filters required clarification to permit an asbestos fiber count, thus providing more \ accurate fiber mass defcerminotion, but obscuring the actual fiber size distribu tion: Therefore; .the calculations of fiber concentration (Table 1) were expressed as asbestos mass per unit inass of lining wear dust and asbestos mass per unit . ! *< mass .of lining worn. Asbestos fiber concentration in the ambient air (background) 1 _V and ir the brake exhaust air*(test) was calculated in units cf nanograns (10 71 grams) per cubic) meter of air. However, the actual asbestos emissions from brake usage , l would be diluted substantially through mixing. The asbestos concentration in urban air due to brake(usage was estimated, based upon existing automotive exhaust lead dilution data. These calculations appenr in Appendix III. * All the test results in Table 1 have been reported as ten times the calculated test values, to allow for possible losses in collection, processing, and counting. These values, therefore, should provide upper bounds for asbestos emissions ..from broke usage. For example, the local (SctrcJt, Michigan) atmospheric ' asbestos concentration ranges from 0-5 to 15.4 nanograms per cubic meter. The .I ohlhervodN'h<i<;kground asbestos value was 1.0 nr7m3, for the normal use test, but is reporued in Table 1 as 19 ng/m3. The low asbestos emissions from .the test disc brake ynder "normal use" conditions is underscored by the addition of but 13 ng/m3 (1-3 ng/m^ observed) in the undiluted exhaust air stream. 1 *' * ^ '' '1 t/1ble 1 ' asbestos emission's from "kqrmal use" braking . Dynamometer Data for a Production Disc Brake* . Background Asbestos in Ambient Air <19 x 10"0 g/m3 . ,Asbestos Fiber frpm Brake in Exhaust Air <13 x 10 5 g/ra3 . Total Asbestos Fiber in Exhaust Air <32 x 10"3 g/W3 v . Estimated Bijake Asbestos Fiber in Urban Air <0.07 x 10~fl g/ra3 . Asbestos Fiber from Brake ih Airborn Wear Dust . <0.055i 11 j ' ; Asbestos Fiber Released from Lining Wear <0.024 , , , * Reported values are'10 times the observed test , values to provide upper bounds ! 1i 1 " The lining wear rate during the first 82 breakin stops was found l to be about five limes ebove the "normal use" rate. Asbestos fiber release during breakin was also highey, an average sevenfold increase. However, since the breakin wear is less than 1$ of the total lining wear, the increase of emitted asbratos fiber resulting from this temporary sevenfold increase would be about 3$,, when averaged over the life of the linings. High temperature br-ike U3nge "Iso increased lining wear rates, in this care,by a factor of eleven. Asbestos fiber emissions increased by less then a' factor cf three. Frequent vehicle operation under such hi)jh temperature 8- - f'Midltions would lower lining life to levels far below present averages. Hdwever, even if. all brake wear provided the^ same fiber emission rate as found in the'high temperature use test, the percentage fiber release to the atmosphere would stjll be under 0,06$ of the lining wear. . * 'i i The remaining brake wear was a mixture of non-fibrous organic and i inorganic matter. Forty-seven percent ?f the estimated 62 to 77$ collectable wear debris were accounted for by the test filter on the normal use test, The remaining 15 to 30$ presumably were retained on the lining-edges, the caliper, spindle, rotor, wheel, and tire. Accurate measurement of this material was not possible, due to the added retention of dust from the ambient air. `\ , More precise values of brake lining asbestos emissions or the determination of their particle size distributions appear possible, for these low fiber concentrations, only by testing brakes in an asbestos free atmosphere. This approach was used in an EPA sponsored study (9)1 where pre-filtered air wap flawed through sealed brakes at a flow rate greatly reduced from normal. CONCLUSIONS 1. ' Automotive brake rusage provides a very small emission of asbestos fiber N , ' (less theta 0.02$ of the lining worn). t i. 2. Automotive brakelusage provides a very small asbestos fiber input to urban atmospheres (estimated to be below 0,07 ng/n3). 3,. Intense local heating and severe local mechanical action causes the decom position. of most asbestos fiber in brake linings during typical usage. 1, - ID S',\n-LE FILTER PREPARATION Microporous membrane filters with Q .^i 5 um pores were selected to ns sure \ higt retention of asbestos fibrils and most of the wear dust powders. A matched pair olf Gelman sampling pumps and 35 mm diameter holders were used. , i ' 't Thin,metal cones of l2 included angle were fabricated and sealed to the ,filter entrance. These cones increased the tip entrari.ee velocity bo that of the exhaust air duct so isokinetic sampling could be achieved. The cone -tips were carefully matched in size. Flowmeters and differential pressure i indicators were installed in the system to monitor the filter airflow during each test and to set the tip entrance velocity before each test. 1I Tests were performed on the unused filters to determine their vc!ght change with variation'of humidity. , Filter weights were measured on a Mcrobalance to the nearest 10 raicrograms. Filters were placed in the center of the designated exhaust duct grid and at a fixed position upstream of the brake, but below the diffuser screen. This latter (background) filter was located where the upstream air velocity equalled the average over the test grid. In this way the sampling was isokinetic with essentially equal Volume flows through both filters.I ' TEST PROCEDURE All brake stops were conducted from the same speed equivalent (40 MPtI, or 18 m/s) tp maintain fixed air flow conditions. Burnish and "normal Pse" brake applications were at 0.25 "s" (2.4j m/s2) deceleration and with r> two minute time interval. .This provided r> peak rotor temperature i of 180C (35'3F) The number of brake applications were selected to provide about one gram of lining wear per test. , Breakin wear was monitored for the first 82 stops. No sampling i, was performed for ahout 200 more brake applications, while the linings and rtT r? QWol f*r\r*A ^ 1 -- "' I '' . ' -11- \ The '`normal use11 test wan then performed on this burnished brake assembly. Twenty brake applications were made under the samp conditions, with the tes-f; filter located sequentially at each of the twenty-eight grid locations. The filter cone entrance velocity wan adjusted to match the grid '* 'I * Velocity at each relocation.Four grids were U3ed to monitor exhaust velocity. 1 Slight adjustments were sometimes required to compensate for drift which appeared to be external wind initiated, .A third test was performed to provide an estimate of the fiber emissions from a hot brake assembly. As in the brenkin test, the test filter was positioned in a central location for this procedure. Thirty-one stops wef-e made at 0.5 "g" (h-,9 m/s2) and^minimal time interval until the rotor attained tlO'JC (7T0F). This temperature-was then maintained by adjusting the application time interval. Ten additional stops were made as the brake - was allowed to cool. , - All filter weight determinations were performed at equilibrium conditions and then corrected for humidity. After use, the fillers were individually stored in covered glass containers. Lining weights were taken after removal of weaif1 debrjs but before they had cooled completely, to ' minimise weight changes from water absorption. -J stored in a dry Jar,- ' Between tests the linings were The relevant test data are included in the following table. A '1 slight pad drag caused the outboard' lining to wear aoovo expectations on the "normal use" test. Since this added.work was not included in the lining wear rate calculations, the specific wear is above the usual range for this lining. No adverse effect' on the test results would bo expected to have resulted from this drag. Similar ped drag effects may occur cn cars, when smooth road conditiohs prevent "pad knockback." Test Brake Speed, REM Brake. Jecel, "g" J Wheel Lpad, kg Brake Applications ' l Total Energy', kW-h Max. Apply Temp, C Total Lining Wear, g -L-ining Wear Rate, g/kW-h Brcnkin Nnrir<nl l Jr. a HI Temperature U,1 535 (40 MHl) 535 (40 mpu) 535 (40 KPii) 0125 (2.45 m/n2) -0.25 (2.45 m/sa) 0.50 (4.9 m/s2) 257 (567 lb) . 257 (567 lb) ' 257 ( 567 lb) 82 f 560 ill - O.938 (1.25 hp-hr) 6.405 (8*54 hp-lir) 0.4 6 9 ( 0.625 bp-t- 115 (240F) 1.10 ia-Mo-csi glhr, 115 (240dF) 1.60 0.25 (0.0U 410 (T70F) 1.07 2.28 (0.100 gfhr i * ) t I I * i ,i . SAMPLE EXAMINATION -35- ' APPENDTK II . 1 ' PREPARATION AND EXAMINATION OF ASBESTOS CARRYING SAMPLES FROM TEST fAt1R3* *' ' 1. All slides, dirfhes, scalpels, and other utensils used in the following 1i , x preparations were cleaned in acetone, followed by rinse in 200 proof ethanol. , - 2.' An area of measured dimension was selected at random from the test filter, * cut end placed particle side down on a clean glass slide. 3'.' Several drops of acetone were placed on tho filter segment to partially dissolve and secure it jto the plate. 4. The. samples were ashed for a,period of two hours by using a low temperature !* asher at a chombeh pressure of 0.5' torr (70 Pa) oxygen and power of 200 watts. .. 5. Several drops of a 1# solution of nitro-cellulose in amyl acetate were i placed on the residue, and a clean watch glass was used to grind the mixture for a ueriod of five minutes. , *_ 6. A second clean glass dlide *;as then placed over the mixture of nitrocellulose and residue, and a "smear" obtained by pressing the two slides together and i . then sliding them apairt. 7. The films thus formed,were permitted to dry andthen removed by scoring the . edge of the slide with a Bcalpel and "floating" the film free from the slide in a distilled water bath. It was found that the film was most easily removed from^ the slide introduced in Step 6. * Sample preparation techniques outlined below are similar to those reported by Selikoff', el ol. ip Reference 2.  JL**- '8, Approximately. 10 el.cfc'ron mlcrosccoc grids (3 nm, fender grids) \ % 1 % , were pieced at random on the floating film, and the film was lifted by putting a .clean slide on ton of the film and drawing the slide down through . N . i the water so as to trap the grids between the slide and the film (which should now cling to the slide). S't* I 1I tl 4 9, A carbon layer of approximately 0.06 Um was deposited on the film to k* ( . ` orevent charging during examination in the transmission electron microscope (TF.M Direct examination specimens were prepared by depositing a carbon layer bn the du3t side of the test filter and dissolving the filter in acetone. Electron microscope grids were used, both to support the Btunple and to provide grid location reference barks. * l I. 1i A il 1 1J . TEM EXAMINATION AND COUNTING 'K0CFDUHE3 'i Approximately ten electron microscope grids were prepared for each of the five filter samples analyzed. Four grids were arbitrarily selected from each sample and two grid squares on each grid were sconned for asbestos. The individual grid squares ere approximately SO um on each 3ide and were examined at a TEM magnification of about 4-0,000. Tor each grid area scanned, \ h' photographs were taken where possible of the first, last, and one randomly ' `\ ' chosen fibril for the curpose of determining an average fibril diameter accurately. 5' - Measurements were Lhep mede visually; that is each fibril, fiber, or asbestos bundle was compared to known calibration marks on the electron microscope screen * 1 to estimate the lengths. The length could be estimated to within 20%, as determined by :lie photographic measurements. The marks on the screen cure 0,5 cm apart corresponding to 0.123 um when a magniliention of 40,000 is used. This approach was taken because it was impractical to photograph all the fibrils and, furthermore, length measurements were not as critical ns diameter measure ** , ments in determining fiber volume. Where both measurement', methods were used, 1 the values providing the greatest indicated brake asbestos levels wore chosen. -1.5- SBniple t I, ' C' 1D E I F ASBKSTOK CONCENTRATION ON FILTERS Sample Identification , Concentration (ng/cm5 of filter) Test-normal stop-new brakes 15*32 Background for A i Test-normal stdp-burnished brakes Background for C 1.06 7*9^ 4.64 . Test-high temperature stop-burnished brakes 5*37 Background for E - not used, insufficient semple Blank - unused filter 0.33 ' From photographic measurements of 120 chrysotiie fibrils, the. asbestos fibr'il average diameler was determined to be 0.0337 with distributions similar to that observed by other workers (10). From 45 fibrils of triple jet- railled chrysotiie- the average diameter was determined to be 0.0316 htn with l' i ''tahdard deviation of O.OO63 wn* ASBESTOS IDENTIFICATION . . Asbestos can bp identified in the transmission electron microscope > *( in. one of two ways. The first and absolute method is by electron diffraction. Such a diffraction pattern is presented as Figure 8. Measurement of diameters and correlation of these measurements with a known standard gives the interclanar '1 spacings of. the material. Comparison of these spacings with the ASTM file identifies the material as clino-chrysotiie (asbestos). . 'The second method of identification is by appearance. Figure 9a % represents an image of asbestos obtained in the TEM. Fine lamellae are observed within the fibril which are parallel to the long axi3. This appearance , , is characteristic of chrysotiie asbestos fibrils. Because of the nature of the electron beam, radiation pzlq heat damage enn occur in the nnteriol markedly -16- \ a change;- in asbestos me represented in Figure 9^. the fibril of Figure 9a hQS been changed to a , .ta and calculated . Temp Use Calculation St Rkgrd Rasic 564 0.564 Measured t-- CM 0.00 Measured 3T 0,12* Measured 33 0.33 Meenured .62 9.62 Measured .48 1.07* f (3)-(4)] X (5) .96 1.<J0 (6) - (1) X .1 6(7) 7.4 (6) x (1) 235 From Mean. .0586 070 005516 (9) x (10) Measured (11) * (12) x ICC .27w* 6(2) 33 1.018ft (10) x (14) (1L) * (15) X ICC (15) * (12) :: ICO to insufficient sample -18- ELTIMATTON OF DRAKE LINING ASBESTOS D: LOTION IM URBAN ATMOSPHERE . The concentration of asbestos fiber from the broke lining" wear debris 1' i . is assumed to be the same as was found in the "normal usage" dynamometer test ., and to be dispersed and have the-.same residence times as the lead emitted from 'i j the engine. Assume an average mileage of 15 MPG from cars which emit 75$ of l" the lead to the.atmosphere. When gasoline averaged 2.52 grams of lead per gallon, the typical lead, concentrations in urban atmospheres were about 2 ng/m3 (JAPCA, Sep. i960, 19j. p. 684). Typical U. S. cars wear 202 grams of lining per year and drive 10,0Cfc miles per year. 1 Ihe "normal use" dynamometer tests provided asbestos fiber amounting to 0,0023$ (.3 x 10"=) of the brake lining worn. ' Allowing a factor of teri to provide an upper bound in this determina tion, the asbestos concentration in urban atmospheres from brake wear should be less than . 10 (2 3 xx 10-=) IV ) fV_1E0?^20_0S0 ^ nJ [LEJ* g p, , . J or 0.07 nft m 2.5S|^ (.75) . Urban atmospheres vary in asbestos fiber concentration from city to !. cit^, within, a city, and from one time to another. This variation does not I correlate with expected automobile-brake usage. The concentration has been I reported to reach 100 jjj (2). Thus it appears that the wear of brake lining produces, at most, a'email fraction of the asbestos fiber in urban air. This is not surprising when one considers that brake lining wear involves only 1.5$ of J. jS. a3bestob usage and that brake usage converts over 99*95$ of this to non*-fibrous dust. Ii -10- , .I CALCULATIONS 0!-' 1 `SELECTION EFFICIENCY LINING COMPOSITION ESTATE FP.OM IiABORATORY ANALYSIS Si02* .1 MgO. Feg03 AI2O3 , HgO CaCOs Zn Organic Total 16.3A 17.8 1 2.5 0.3 J 5-5J 15.4 3-9 100.0% Chrysotile Asbestos '(-2.4% ,' \ WEAR DEBRIS ESTIMATE ' Decomposed Asbestos ' Decomposed. Limestone Zinc Metal ' Inorganic ' ORGANIC 1 t J Volatile Uncertain i . Low Volatility Organic Collectable Total Collectable , Collected on Filter Collectable Material i\%>~ tt>'v:vV\ 36.9*. 8.6$ 49. H 10.5$ 35-7% ' 12.1% 12.1$ to 27.Bi 61.5^ to 77.2$ hi% l4.5'{. to  1 ,I RE!ERKNCEG ' 1 1. Sullivan/ R. J. et al., "Preliminary Air Pollution Survey of Asbestos," . i ' II.A.P.C.A^ jPublication APTD 69-27, U9&9). I 2. Selikoff, E. J., ot al., "Asbestos Air Pollution," Arch. Environ. *i * .t Health, Vol. 25. (July` 1972). . . ' 3. Thomson, J. G., "Asbestos and the Urban Dweller," Ann. N. Y. Acad. 5ci., 152:196 (1965). 1, 4. Lynch, .T. P.., "Brake Lining Decomposition Products," .T. Air Pollution Control Assoc. l8;l (1968). 5. Luxon, S., "Technical Implementation of the New Asbestos Regulations," Ann. Cccup. Hyg. (Brit,) Vol. 13 (1970). 6. Rabinowicz, E., "friction and Wear of Materials," John VJiley, (1565)* 7- Anderson; A. E., "Wear in Brake Materials," ASHE V/ear Conf., (1969). 8., Anderson, A, E.," et al.', "A New Laboratory Friction and Wear Test for the Characterization of Broke Linings," SAE Trans., pp. 56l-9, (19^8). 1 9'. Tncko, M, G., et al., "brake and Clutch Emissions Generated During Vehicle Operation," SAE Preprint 730548, (1973). , .1 10. Yada, K., "Study of the Microstructure of Chrysotile Asbestos by High l . Resolution Electron Microscopy," Acta Crystal, Vol. A, 27, (1971). Figure 1 ,t Figure 2 Dynamometer tort schematic. Dynamometer test setup. ' Figure 3 i li'gure1 k k Figure 5 View'of br&ke assembly and test grid. i .( TEM image of chrysatile asbestos fibers. TEM image of partially opened fiber bundles. . Fjgure 6 TEM image of fiber bundle on "normal use1" filter. Figure T TEM image of fibril on "normal use" filter. 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