Document oevDqQyQ39v2ZnK7wED89NgY7

FILE NAME Allied Signal Bendix ASB DATE 1973 DOC ASB036 DOCUMENT DESCRIPTION Report - Society of Automotive Engineers - Brake and Clutch Emissions Generated During Vehicle Operation 730548 Brake and Clutch Emissions Generated During Vehicle Operation Michael G. Jacko Research Laboratories Bendix Corp. Robert T. DuCharme Automotive Control Systems Group Bendix Corp. Joseph H. Somers Office of Air and Water Programs Environmental Protection Agency THE CHRYSOTILE FORM of asbestos is a major constituent in automotive friction materials disc pads brake linings and clutch facings Asbestos is used because of its thermal stability relatively friction level reinforcing properties and low cost During operational engagement in the vehicle the friction material and a metal rotor forma sliding friction couple which converts the kinetic energy of rotating members into heat absorbs the heat and gradually dissipates it to the surroundings Friction material emissions are generated by wear Abrasive and adhesive wear are considered to be the most important mechanisms below approximately 450 thermal wear predominates above 450 The organic constituents pyrolyze of oxidize and are emitted to the air as carbonaceous solid particles or gaseous reaction products The asbestos fibers are pulverized into small particles which are either trapped in the brake or clutch housing fall to the road or are emitted to the atmosphere Most of the asbestos is heated to temperatures high enough to cause chemical conversion and is therefore trapped or emitted as olivine or forsterite particles When the large number of existing cars and trucks is c^n sidered each with eight or more pieces of friction material in ABSTRACT In order to define the extent of gas and particulate emissions from automotive brakes and clutches a combination separa- tion and storage collection system was devised Unique emis- sions collectors for both disc and drum brakes and for a clutch were conceived designed and built as the main embodiment of this instrumentation The hardware was installed on a ve hicle which was then driven through various test cycles to determine the extent and type of brake emissions generated at low- and operating temperatures Typical driving condi- tions such as the Detroit Traffic Test as well as more abusive driving conditions such as fade tests were included Typical original equipment and aftermarket friction materi- als for both disc and drum brakes were used in the tests Copyright Society of Automotive Engineers Inc. 1973 All rights reserved Brake relines were made to simulate typical consumerits pe practices The brake emissions generated were removed the various collectors and mass balances were performe : The particulates were processed and analyzed by combina : - optical and electron microscopy to ascertain the asbestos asbestos content and the asbestos particle size distribution in - + 7ar debris Comparisons of emissions from new and used in n materials from disc and drum brakes and from origina najp- najp- najp- ment and aftermarket materials were made Finally an eats mate was made of the total emission of asbestos by all the > vehicles in the country On the average more than 99 f the asbestos is corverted The contribution to the atmosphere is 5060 lb or 3.2 of the total asbestos emission 2 the brake system plus more in the clutch mechanism it becomes apparent that an air pollution problem may exist Considered in another light there are perhaps 1 billion pieces of friction material in vehicles in the United States gradually being pyrolyzed and ground to dust The brake systems in the vehicles utilizing these friction materials can thus be consid ered as chemical reactors each emitting organic and inorganic compounds including asbestos and its decomposition products to the atmosphere The compositions of the gaseous and solid emissions are not known nor are the particle sizes and shapes of the solid emissions known has never to the authors knowledge been reported in the lit- erature To define the extent of these emissions a collection system was devised which combined the functions of separa- tion and storage Unique emissions collectors for both disc and drum brakes and for a clutch were conceived designed and built as the main embodiment of this instrumentation The collectors separated the wear debris into three different fractions a sump sample which included the wear debris on the lining surfaces in the rivet holes and on the brake drum a surface sample which included the wear debris on the brake and collector shroud surfaces and an airborne sample col- lected on membrane filters OBJECTIVES Because of the possible damage which asbestos emissions can produce in the human respiratory system it is desirable to identify and quantify these emissions Thus the objectives of this paper are to 1. Describe the methodology used to generate collect and analyze brake and clutch emissions 2. Report the asbestos contents in emissions from a test ve- hicle 3. Estimate the total asbestos emissions for all vehicles in the country TECHNICAL APPROACH The major requirements for the emissions sample collection system may be summed up as follows Collect all particulate and gaseous emissions 2.2. Store collected emissions unchanged 3. Prevent intrusion of contaminants 4. Maintain ordinary braking and clutching conditions 5.5. Be operable at high temperatures 6. Permit easy separation and analysis of emissions MATERIAL SELECTIONS- For the results to be represen tative of average consumer vehicle usage a vehicle inter- mediate between compact and luxury was selected The vehicle was equipped with front disc brakes rear drum brakes and dry clutch All friction material used contained asbestos Three vehicle tests were run The detailed technical approach may be summarized as follows 1. Select a suitable vehicle and linings representative of the marketplace 2. Conceive design and build brake and clutch emissions collectors 3. Test and check out a typical collector on an inertial dyna- mometer and install instrumentation on the test vehicle 4. Select and run suitable driving test schedules representative of consumer driving 5. Collect and analyze emissions to obtain the asbestos content and the particle size distribution 6. Estimate the asbestos emission for all passenger vehicles and extend the data to trucks to obtain a result for all vehicles operating in the United States A passenger car was selected for testing because of the following factors 1. Vehicle braking cannot be simulated realistically on small scale friction test machines with the present state art 2. scale brake and clutch dynamometers provide fairly good simulation and can be used for checking out the emissions collection system however separate tests for brakes and clutches would be required thus increasing program costs On the vehicle disc and drum brakes and clutches can be tested simultaneously INSTRUMENTATION METHODOLOGY AND CRITERIACRITERIA The collection of par ticulate and gaseous emissions from any vehicle friction couple The first vehicle test was run with the original equipment friction materials The second vehicle test simulated a partial fronts only relined the rears were repeated to give a replicate test and an indication of emissions trends for friction materials with continued use The third vehicle test simulated a complete brake reline and included turned discs and drums The friction materials selected for the program were representative of those supplied by the industry different manufacturers Abex Bendix Manhattan Thiokol and Worldbestos produced the original equipment and aftermarket disc pads and drum linings which were selected in part because of their volume usage VEHICLE INSTRUMENTATIONINSTRUMENTAION A passenger car of me dium weight 4850 lb test weight produced in high volume was selected It was equipped with a speed manual transmission ventilated iron disc brakes on the front and iron drum brakes on the rear This vehicle was selected in order that the emissions from clutches and from disc and drum brakes could be tested simultaneously on a vehicle size representing a large percentage of the present vehicle popula tion The vehicle was equipped with standard brake test instru- mentation A front disc brake collector and a rear drum brake collector were installed on the right side of the vehicle The clutch was sealed by closing the few holes in its casing The left wheel brakes were left in their normal configuration and were used to monitor the operation of the shrouded brakes Wear debris was taken from the left brakes as well as from those on the right The amounts of debris formed and their compositions were used to demonstrate that the brake shroud- INLET AIR FILTER CARRIER AIR PARTICLE FILTERS HEATER COILS COLLECTIONCOL ECTION COL ECTION SYSTEM FLOWMETER VACUUM MANIFOLD AIR PUMP Fig 1 Schematic diagram for airflow of typical particulate and gas collection system 17 PLACE ETHERMOCOUPLE SWITCH Cam CLUTCH GAS PE COLLECTION COLLECTION COLLECTION SYSTEM ; GAS COLLECTION SYSTEM HOLD DOWN STRAP FRONT SHARE GAS COLLECTION SYSTEM " THERMOCOUPLE JUNCTIONS FRONT BRAKE INLET AIR DRIER AND FILTER 2 Fig 2 - Vehicle instrumentation front seat area VARIAC TO CONTROL VOLTAGE TO HEATERS INLET AIR ORIER AND FILTER Fig 3 - Vehicle instrumentation rear seat area CALIFER af rE = Boe ROTATING SEAL |_| IMODIFIEDI TO !~ mez STORAGE LIMIT Se | Fig 4 - Schematic of disc brake shroud 4 ing did not significantly affect the operation of the brakes on the right side EMISSIONS COLLECTION SYSTEMS OVERALL SYSTEM DESIGN - The basic design concept of each brake emissions collection system is shown in Fig 1 Air from inside the vehicle was pulled through a bed which removed water and carbon dioxide from the air The air then passed through a filter to remove all particles larger than 0.2 m8 x 100 in The filtered air was then routed to the sealed brake assembly through clean Teflon tubing The airstream along with wear particles and gases then passed out of the brake through Teflon tubing which was heated to avoid condensation This stream passed through two filters to remove the airborne particles and preserve them for analysis The stream then passed through three cold traps in order to condense and trap the gases evolved during braking and preserve them for analysis The remaining airstream then passed through a flowmeter the vacuum manifold and finally through an air pump run by the vehicle engine where it was expelled to the atmosphere Fig 2 shows mounted in the front seat of the test vehicle the front brake inlet air filter and gas collection system the clutch gas collection system and the 12 position thermo- couple switch and pyrometer used to monitor gas and filter trap temperatures Fig 3 shows as mounted in the rear seat of the test vehicle the rear brake air filter and gas collection system the clutch air filter and the electrical system bat- OUTBOARD SHIELD CALIPER TOP COVER SPINDLE MODIFIED DUST SHIELD SILICONE NUBBER SEALS gt AO as eg: pn ete pantaauaonpabhad jabs wit don : te. Fig 5 - Disc brake emissions collector exploded view S teries inverter and Variac which were used to supply power to the heating coils PARTICULATE FILTERS - The 47 mm filter holders joined in series were used for the collection of airborne particulates Nuclepore filters were used These filters are made from a smooth film of polycarbonate plastic with pores that do not restrict the flow of gases significantly as particle collection proceeds The filter holders were heated by tape heaters wound around the outside and controlled by a variable trans- former within the test vehicle GAS COLLECTION SYSTEMSYSTEM Three gas collector traps held at approximately -70 -70 -95 were used A simple finger trap placed first was used to remove and store the condensable vapors These vapors included most of the or- ganic degradation components from the brake lining The second type of trap of which two were used contained acti- vated charcoal and was used to collect the volatile hydrocarbons such as methane and other light gases DISC BRAKE COLLECTORCOLECTOR Fig 4 shows a sectional view of the disc brake collector The rubbing seal was located at the hat or hub section of the rotor The seal was a spring- GRAPHITE PILLED TEFLON SEAL WAM SHROUD THERMOCOUPLE BLACK OXIDE | COATING WATER SPRINKLING SYSTEM . a tO me AXLE / J +- _ BRAKE PAD THERMOCOUPLE > a . = POWER LEAD ne a . Fig 7 - Back view of disc brake emissions collector showing instrumentation loaded graphite Teflon seal of commercial manufacture A view of major components of the collector is shown in Fig 5 the system as mounted on the vehicle is shown in Figs 6 and 7. The main portion of the shroud was coated with black oxide a cooling system was added and an open mag wheel was used to aid in cooling the enclosed brake DRUM BRAKE COLLECTORCOLECTOR Fig 8 shows a crosssectional view of the collector along with the detail of the rubbing seal The seal was of the same type as for the disc brake collector The axle hub used to align the drum was modified with a piece that was concentric to the axle bearings within 0.001 in 0.0025 cm A tapered lead was used to facilitate mounting of the drum The close tolerances on the concentricities were necessary in order to obtain reason- able seal life Figs 9 and 10 show outboard and inboard views of the system as mounted on the test vehicle CLUTCH COLLECTOR- Th"clutch system consisted mainly of a filtered air inlet and an outlet to the sample storage system with all other external holes sealed INERTIA DYNAMOMETER TESTS The front disc brake emission collector was tested on an in- ertia dynamometer to check out its operation and its most critical part the rotating seal Thermal response tests were made with the results indicating that for normal operation the shrouded disc brake would operate at a slightly higher temperature than the normal brake configuration A method was devised to determine the leak rate of the collector The rotating seal was largely responsible for the residual leak the leak rate was reduced significantly by use of a very small amount of hightemperature grease The rotating seal underwent durability testing and survived 7 h at 50 mph A second series of dynamometer tests gave reproducible emissions and temperatures Finally a test was made in which the collector and especially the rotating seal were shown to be relatively tight to external liquid and particulate contaminants VEHICLE TESTS RATIONALE- For a given vehicle brake system friction material wear is primarily a function of the duty cycle For duty cycles where pad and lining temperatures remain under 350 low wear results and is primarily due to the abrasive and adhesive wear mechanisms Heavier duty cycles at higher temperatures give some combination of thermal abrasive and adhesive wear Under severe heavy duty where the use borders on abusiveness brake fade may occur The inability of the brakes to hold the friction level results in part from the formation of gases and wear debris at the interface Although there are many acceptable original equipment manufacturers friction material tests to measure a specific condition or combination of conditions there is no one test which adequately matches normal driving conditions which would be representative of all vehicles Consequently it became necessary to devise a rational and meaningful vehicle test driving schedule SELECTED VEHICLE SCHEDULES A total of seven test schedules were chosen and each was followed by a measurements procedure take emissions samples measure measure wear inspect systems and replace worn parts The first three Burnish Burnish A.B. Baseline and Detroit represent the temperature tests The final four tests Stop Fade After A.F. Baseline AXLE SEAL AND STATIONARY SEAL RING Fig 10 - Inboard view of assembled rear drum brake emissions collector T 15 Stop Fade and Final represent the temperature tests Burnish - During the Burnish the original equipment and aftermarket linings mate and conform to the initial condition of the rotor whether it is in its original configuration used condition after vehicle test 1 or its turned condition prior to vehicle test 3. It was anticipated that the emissions during Burnish would be different from those for worn linings A.B. Baseline - This consisted of three days of Detroit Traffic Test It was run at this time so that the other Base- lines run at later times could be compared with the A.B. Baseline for the amount and type of emissions Detroit Traffic Test The Detroit Traffic Test is typical of urban driving and is used primarily to evaluate friction life and noise of commercial brake products The normal operating range passenger car brakes in the test is 180280 This condition constitutes what a brake engineer calls a temperature wear test Testing is intentionally accelerated to reduce test costs consequently the test tends to be more severe than average driving The end of the Detroit Traffic Test was the end of the temperature wear testing 10 Stop Fade and Recovery - The 10 Stop Fade and Recovery was the fourth test sequence and the start of the heavy or temperature testing During this test the front brakes experienced temperatures above 500F while the rear brakes experienced temperatures above 350 F The combination of increased temperature and increased duty was expected to change the amount and type of wear debris generated as compared with the previous duty tests The Fade and Recovery Test was then followed by the Reburnish sequence A.F. Baseline - This fifth test sequence was identical to the second and seventh test sequences and similar to the third but only the conditions of the friction materials had changed This test was expected to determine the permanent changes in the amount and type of wear debris generated for friction materials taken through temperature and heavy stops 15 Stop Fade and Recovery . The sixth test sequence was the 15 Stop Fade and Recovery in which the friction materials were taken to even higher temperatures than for the 10 Stop Fade The five additional stops performed after the brakes were already hot produced temperatures above Table 1 Comparison of Disc Brake versus Drum Brake Operating Conditions Parameter Disc Drum Type of system Airflow Emissions . Third abrasive wear Open High Relatively few trapped Relatively none Closed Low Much trapped in surfaces and in sump Some 575 This is abusive braking and rarely occurs The emissions generated were expected to be different again as com pared with the duty tests and the 10 Stop Fade The Fade and Recovery Test was then followed by the Reburnish sequence Final Baseline - The results of this seventh and last test sequence can be compared with the results of the identical second and fifth test sequences This test concluded the determination of the effects that temperature and heavy tests have on brake emissions SAMPLING AND ANALYTICAL PROCEDURES GENERATION OF EMISSIONS . During the braking process particulate emissions are generated by the rubbing action of the friction materials and the rotors The original equipment manufacturer OEM brake configurations left wheels of test vehicle release emissions which reside in either of two areas depending on the brake type Table ) The disc brake releases much of the emissions to the atmosphere while a small amount remains in the brake The drum brake re- leases a smaller amount to the atmosphere and retains sizeable portions on the rubbing surface and on the brake parts The brake emissions collectors perform two functions not encountered in normal brake operation they collect all the debris generated and fractionate the debris Table 2 summarizes the particulate emissions samples produced The OEM brake configurations release gaseous emissions which again reside in either of two areas Most of the gaseous emissions are released into the atmosphere some of the high molecular weight materials distill from the hot surfaces and condense on the cooler brake parts The emission transfer lines used in conjunction with the collectors therefore were heated so that almost all gaseous emissions could be transferred to the gas collection traps PARTICULATES REMOVAL FROM COLLECTORS A detailed step procedure was prepared for the removal of brake emissions from the collectors The amounts of debris collected at the various locations were used later to calculate the mass balances A detailed step pro- Table 2 - Samples Produced by Brake Emissions Collection Sample Disc Brake Drum Brake Sump Surfaces Airborne Trapped debris ^fincludes that in rivet holes on pads and in caliper piston Accumulated on shroud- normally road dropout Airborne samples col- lected on filters Trapped debris - includes that in nivet holes " linings and on drum surface Accumulated on brake sut- faces Airborne samples on filters lected Normally not completely released during brake operation . This may be a controllable material which could be disposed of properly Provides body wear 8 cedure was also prepared for the sampling handling and analysis of the asbestos emissions ANALYTICAL PROBLEM - DEFINITION The thermal and mechanical forces which act at the friction couple inter- face produce a complex chemically and physically altered microstructure which cannot be accurately described at present Table 3 gives an estimate of the chemical composi- tion of wear debris Asbestos is a complex inorganic material with the approximate composition formula Mg3 SiO OH or 3MgO 2SiO2 2H O The basic unit has a fibril form 1 2 Asbestos is readily identified when alone or in simple mixtures at high concentrations by these analytical methods ray diffraction thermal methods microscopy and infrared analysis However in complex mixtures or at very low concentrations the analysis for asbestos is very difficult In brake wear debris the problem is compounded because the reaction products of asbestos forsterite and olivine have similar elemental ratios and similar ray diffraction patterns The only sensitive method which can be used is microscopy In extremely low concentrations asbestos is identifiable in the electron microscope by its physical shape tubular fibril which is distinguishable from that of other fibers and particles At the beginning of the program one optical 3 and three transmission electron microscopy 4-6 methods had been developed by others Two of the electron microscopy methods were not suitable because they changed the fiber size dis- tribution of the asbestos larger sample collected the analytical steps could not degrade the particle size distribution of the asbestos fibers obtained the results obtained must be indicative of the actual asbestos content of the sample These criteria were met by the analytical scheme outlined in Fig 11 Representative Sampling and Temperature Ashing LTA The analysis of brake wear debris indicated the presence of 20-30 by weight of polymeric and carbonaceous material which in turn produced a fluffy appearance when the material was examined in the scanning electron microscope The organic portion was therefore removed by LTA Two representative samplings were used the first in sample selection for LTA and the second in sample selection for distribution on a filter membrane for subsequent analysis Selected Microscopy Methods - In the very early tests wear debris from a sample dynamometer was collected on the filter train of the 8.0 and 0.2 Nuclepore filters Both filters were examined by a combination of optical and transmission electron microscopy The following observations were made 1. Asbestos fibers longer than 20 ...were obtained 2. Very fine fibrils were extremely difficult to detect at less than 5000 diameters magnification Based on the above studies it was deemed necessary to employ two magnifications To detect fibers greater than 2 ...a magnification in the range 10,000-40,000 diameters SAMPLE SURFACES SAMPLE WEIGHED AIRBORNE SAMPLES DZMFILTER = 3.0M FILTER ANALYTICAL METHOD SELECTED - From the available analytical methods and the problems associated with brake wear debris analysis the following considerations were necessary Criteria and Flow Chart - Three important criteria had to be met by the analytical method used The very small portion of brake debris used had to be representative of the much ISAME AS FOR SURFACES SAMPLEI COMBINE WEIGH REPRESENTATIVE SAME AS FOR FRACTION SURFACES SURFACES LAMPLI | LOW TEMPERATURE ASH LTA Numbers in parentheses designate References at end of paper | WEIGHT REPRESENTATIVE FRACTION | Table 3 - Estimated Chemical Composition Characteristics of Wear Debris Description Low molecular weight degradation products Polymeric components Carbonaceous material Inorganics . Mineral Olivine Oxides from lining Fe fOrom rotor Asbestos Percent 2-10 12-20 1- \ 10-30 2040 0-10 5-15 1 20-30 70-80 | DISTRIBUTE ON 0.2 NUCLEPORE FILTER | OPTICAL MICROSCOPY GLASS SLIDE MOUNT ' COUNT 400X PHASE CONTRAST | DIVIDE f RESULTS | ELECTRON MICROSCO CARBON SANDWICSAH NDWICH COUNT 127.900XI Fig 11 - Flow chart of particulates analyses 9 was required Table 4 shows the magnifications selected for use with the two microscopy techniques Calculations from Microscopy Results For each fibril or fiber found it was necessary to determine its dimensions and calculate the volume of asbestos found Because of the large number of fibers this procedure became tedious To simplify fiber sizing a microscopy count sheet was developed Each fiber found by the appropriate microscopy method was classified into the proper size category containing the projected diameter and length of the fiber in question The volumes were summed converted to weight and normalized for the entire sample weighed onto the filter A computer program was subsequently developed to minimize computational time and to eliminate errors in the processing of these calculations The possible sources of error associated with sample processing and analysis were minimized through use of statistical methods The largest effect found on the asbestos analysis was the occasional occurrence of a large fiber The extent of error increased as the percent of asbestos in the sample decreased The data showed that the maximum deviation for results with asbestos contents above 0.10 averaged 12-15 and had a maximum at approximately 20 The maximum deviation increased for asbestos contents below 0.10 where errors for the small amounts of asbestos emis- sion become less significant from the standpoint of air pollu- tion VEHICLE TEST RESULTS systems Only one major problem occurred during the vehicle testing during the 10 Stop Fade of vehicle test 1 the hardened steel ring on which the rotating seal slides became loose The ring was reanchored and no further problem was encountered during the 15 Stop Fade or in any further test schedule This result showed the durability of the collector and rotating seal design and construction For the 8100 miles of testing only seven front and eight rotating seals were required This was better than anticipated at the start of the program Operating Temperatures Frequent temperature monitoring was necessary for the successful completion of the vehicle tests The temperatures were monitored at all four wheels Table 6 The top portion of the table shows the effectiveness of the thermal control aids in keeping the temperatures of the shrouded disc brake well below the 400 region where the exponential wear rate begins Since approximately 90 of the test miles were driven in the Detroit traffic circuit it was necessary to monitor these temperatures carefully The driver was instructed to take specific actions when greater than desired temperatures occurred For example during the Detroit traffic circuits the maximum allowable temperature was 330 When this temperature was reached the vehicle was stopped and allowed to cool to 300 These down periods were seldom necessary The data at the bottom of Table 6 show that on hot July day the temperature difference between the brakes remains fairly constant as the temperatures increase with the ambient MILEAGE ACCUMULATIONSACUMLATIONS The various driving schedules described earlier are listed in Table 5 with the average mileages and times for each test The overall variation for the total mileage accumulation of all three vehicle tests was very low at 2.4 These mileage variations were primarily due to the varying times taken to reach the Detroit traffic circuit Normally only one round trip was required to obtain the four circuits Rain seal failure thermocouple malfunction and other minor difficulties which required a premature return to base added to the minimum mileage possible PERFORMANCE OF EMISSION COLLECTION SYSTEMS Rotating Seal Life - The success of the vehicle testing depended heavily on the proper operation of the rotating seals since they were the most critical parts of the collection Table 4 - Microscopy Magnifications Selected for Asbestos Fiber Analyses Microscopy Technique Transmission electron at 22,000X Optical phase contrast at 400x Fibers Detected Minimum dx Maximum dx 0.03 ^ 0.10 0.50 x 1.50 0.50 35 10 ^ 100 Table 5 - Summary of Vehicle Mileage Accumulations Schedule Burnish A.B. Baseline Detroit Traffic 10 Stop Fade A.F. Baseline 15 Stop Fade Final Baseline Totals Test 123 123 123 23 123 23 3 3 2 1 3 231 23123 23123 Miles 174 127 100 328 348 368 1439 1430 1355 47 53 58 356 339 347 47 79 52 352 326 352 2756 2702 2632 8090 Average Miles 134 348 1408 53 347 59 343 2697 Days 35 5 135 40 48 15 35 380 Test Burnish Vehicle test 1 A.B. Baseline Vehicle test 2 Table 6 - Brake Temperatures During Burnish and Detroit TraticCircuits Remarks Initial attempt no thermal control aids After 20 stops After 40 stops After 60 stops Rerun with thermal control aids After 10 stops After 40 stops After 60 stops After 100 stops After 160 stops Morning circuit 8:00 a.m. 12 Mile and Woodward Michigan and Thud Adams and Woodward Adams and Woodward 12 Mile and Woodward Afternoon circuit 2:00 p.m. 12 Mile and Woodward Michigan and Third Adams and Woodward Adams and Woodward 12 Mile and Woodward Front Disc Brake Ambient Temperature Right Left F Shrouded Normal AT Rear Drum Brake Right Left Shrouded = Normal / 10 10 10 Range 70 29388 29388 29388 29388 Range 22222 22222 22222 22222 22222 222 222 222 91 91 Range 400 340 360 340-400 150 120 160 120-160 250 220 200 200-250 255 200 245 200-255 150 110 150 110-150 105 90 95 90-105 280 310 265 280 300 265-300 150 150 150 165 170 150-170 130 160 115 115 130 =. 115-160 205 245 215 220 190 190-245 150 165 165 170 130 130-170 58228 58228 58228 58228 60 50-80 270 300 300 280 330 310 320 310 310 300 270-330 150 160 160 150 190 120 140 140 30 140 210 180 180 170 160 100 140 30 140 140 150-210 = 100-140 150 170 180 180 190 160 210 210 200 170 150-210 150 160 160 160 160 160 180 180 170 150 150-180 02889 02889 02889 02889 30 0 30 30 30 20 0-30 tH For the 10 and 15 Stop Fade schedules it was expected that the shrouded brake would retain the high temperatures longer than would the nonshrouded brake In the course of the test it was necessary to increase the time interval after the seventh stops to allow for additional cooling Fig 12 gives the temperature versus stop relationship from the 10 Stop Fade of vehicle test 1. Data taken from an inertia typical vehicle baseline dynamometer and a typical vehicle test were used as baseline data to which the shrouded disc brake was programmed All other fade tests showed similar relationships Mass Balances - The emissions samples were removed from the collectors and weighed The results for vehicle test 1 which are typical of the other two tests are given in Table 7. After each test the brake lining weight losses were also obtained distribution distribution emissions obtained The distribution of the brake emissions was then obtained for the sump surfaces and airborne samples Table 8 summarizes the distributions for the three vehicle tests PERCENT ASBESTOS CONTENTSCONTENTS Each of the samples optical was asbestos analyzed for content by optical and electron microscopy as described earlier For vehicle test , the range of asbestos contents in brake emissions varies high emissions varies from a high of 1.65 down to a low of 0.05 Table 9 Of the 47 analyses reported only two were above The asbestos 1.00 overall average was For vehicle test 2 the range of asbestos contents in brake emissions varies from a high of 1.42 down to a low of 0.03 Of the 43 analyses reported only one was above 0.96 and Table 7 - Weights of Brake Particulate Wear Debris Collected Vehicle Test , Front Brakes Rear Brakes Schedule Right Left Right Loft Collector Shrouded Normal Shrouded Normal Burnish A.B. Baseline Sump Surfaces Airborne Sump 0.142 0412 0.061 0.083 0.116 0.029 - 0.128 0.144 1.170 0.046 0.185 0.220 0.394 - 208 Surfaces Detroit Traffic Sump Surfaces 10 Stop Fade Sump 0.130 0.201 0.580 A.F. Baseline 15 Stop Fade Final Baseline Totals Airborne Airborne Sump Surfaces Airborne Surfaces Airborne Sump Surfaces Airborne Sump Surfaces Airborne Entire test 0.013 0.013 0.191 1.764 0.616 0.120 0.120 0.154 2.011 = 0.375 0.967 13.996 1.195 17.158 0.055 0.458 0.109 0.244 0.076 - 0.153 0.030 0.150 0.027 ~ 0.138 0.083 - 1.387 0.409 - 1.796 0.590 0.436 0.285 -0.335 0.017 0.017 0.060 0.652 -0.046 0.00.00044 0.097 0.440 0.003 0.341 7.375 0.434 0.205 1.654 0.878 1.120 0.275 - -0.516 1.543 -0.330 0.169 - 0.017 = 0.448 = 2.373 3.912 - 8.350 6.285 Estimated from cumulative sample 0.145 g taken during thu schedule only FRONT BRAKES 800 T-~ 500 FIRST INCREASED INTERVAL VEHICLE F g TEMPERATURE TEMPERATURE TEMPERATURE m+ TEMPERATURE 200 = TEMPERATURE TEMPERATURE 100 040 BASELINE 040 RIGHT LEFT 0 i tL. i n a i i rl a oe a i H I 10 7 J i 7 T 1 2 4 6 10 a a 10 12 REAR BRAKES 800 500 ~- F TEMPERATURE TEMPERATURE g TEMPERATURE 300 + TEMPERATURE TEMPERATURE TEMPERATURE TEMPRATURE 200 + TEMPERATURE 100 ~+- 1 T 2 FIRST ut 1 1 i J. 1 4 l rg t TI T T T t T t 4 a r 10 4 a 10 FADE STOP NUMBER RECOVERY j 1 12 Fig 12 - Brake temperature data during 10 Stop Fade Test 12 only three were in the range 0.50-0.96 all others were less than 0.50 The overall av~ t agwe as 0.25 For vehicle test 3 the range of asbestos content in brake emissions varies from a high of 0.51 down to a low of 0.003 Of the analyses reported three were in the range 0.20-0.51 all others were less than 0.20 The overall average was 0.07 For all three vehicle tests the overall average of asbestos content in the brake emissions was 0.23 systematic provide Independent Asbestos Analyses . To provide a systematic independent check on the asbestos analyses the Environmental Protection Agency EPA arranged for Battelle Columbus Laboratories to analyze 24 samples generated during the Program The Manville Research and Engineering Center also provided three analyses 7 In 19 of the 24 slightly higher analyses the Program results were slightly higher than the corresponding Battelle results Table 10 The Program Distribution Emissions Table 8- 8- Distribution of Emissions % Front Brakes Rear Brakes Vehicle Test Collector Right Shrouded Left Normal Right Shrouded Left Normal 1 Sump 6-31 Surfaces 63-89 Airborne Airborne 2 Sump 2-15 2-20 Surfaces 71-93 Airborne Airborne 2-22 3 Sump 2-38 Surfaces 46-86 Airborne 7-19 61-83 17-39 - 63-83 17-37 - 8-22 72-88 36 36 12-22 60-86 1- 2 9-36 61-87 1-11 36-65 35-65 - 39-63 37-61 - ~ 7 - The ranges give the lowest and highest percentage found for the seven driving schedules as a whole Table 9 - Summary of Asbestos Analytical Results Vehicle Test 1 Weight Percent Front Brakes Rear Brakes Schedule Right Left Right Left Collector Shrouded Normal Shrouded Normal Burnish Sump 0.813 - Surfaces 0.398 Airborne 0.144 0.865 0.349 A.B. A.B. Baseline Sump Surfaces Airborne 0.452 1.650 0.472 0.290 0.607 0.179 0.415 0.493 Detroit Traffic Sump Surfaces 0.804 0.247 0.137 0.362 0.129 0.373 Airborne 0.052 0.092 10 Stop Fade Sump Surfaces 0.145 0.463 0.162 0.198 0.280 0.071 Airborne 0.154 0.132 A.F. Baseline Sump Surfaces Airborne 0.260 0.656 0.507 0.134 0.161 0.419 0.242 0.079 0.432 0.247 15 Stop Fade Sump 0.602 0.071 Surfaces Airborne Airborne 1.548 0.175 0.257 0.222 ; FiFninaall BasBealsienleine Sump Sump 0.775 0.775 0.183 0.183 Surfaces Airborne Airborne 0.290 0.167 0.324 0.145 AverageAverage 0.297 0.452 0.452 AveragAveragee 0.351 0.301 0.301 Average value for wheel where collection took place Not indicates that analysis was not required a * 0.991 0.265 - 0.275 0.416 _ hd 0.439 0.472 ~ Otte Vehicle Test Schedule Collector 1 Detroit Traffic Sump Surfaces 10 Stop Fade Airborne Sump Surfaces Airborne 2 Burnish Sump Surfaces Airborne Detroit Traffic Sump Surfaces Airborne 3 Detroit Traffic Sump _ Surfaces . Airborne Averages Program average 0.247 Battelle average 0.171 Ratio Program = 0.69 Table 10 Comparison of Analytical Results for Asbestos Front Disc Brakes Program JM Battelle 0.247 0.137 0.052 0.463 - 0.254 0.402 - 0.186 0.304 - 0.234 0.018 - 0.025 0.204 = 0.005 ~ - 0.21 0.011 0.001 1.22 - 0.31 0.28 - 0.10 0.62 - 0.006 0.135 ~ 0.016 0.265 Rear Drum Brakes Program JM Battelle 0.129 0.373 0.092 0.280 - 0.132 0.484 1.416 - 0.249 0.113 0.115 0.046 - 0.037 0.289 ~ 0.002 0.006 ~ 1 I 0.025 0.006 0.001 0.22 - 0.007 0.10 0.38 - 0.057 0.061 0.015 0.010 = 0.044 0.077 Clutch Program Battelle - 0.291 $ ~ ~ I } 1 J = - ~ 0.007 ~ - I 13 average was 0.24 while the Battelle average was 0.17 or 69 of the Program average The Program data were expected to be higher for the following reasons All farger fibers bundles of fibrils found were assumed to be cylinders of projected diameter and length and a fiber with an elliptical cross section was actually smaller in volume than reported all fibers were assumed to be 100 asbestos Table 11 - Weight of Asbestos Generated During Braking Test , mile Front Brakes Rear Brakes Schedule Right Left RightRight Left Collector Shrouded Normal Shrouded Normal Burnish Sump Surfaces Airborne A.B. Baseline Total Sump Surfaces Detroit Traffic Airborne Total Sump Surfaces 10 Stop Fade Airborne Total Sump Surfaces Airborne A.F. Baseline Total Sump Surfaces Airborne 15 Stop Fade Final Baseline Total Sump Surfaces Airborne Total Sump Surfaces Airborne Total 6.77 9.42 0.51 16.70 0.04 1.04 1.15 223 0.35 1.91 0.09 2.35 57.13 41.77 1.70 100.60 3.52 25.12 0.97 29.61 78.89 1957.40 4.47 2040.76 1.90 24.85 1.78 28.53 * . 8.11 0.92 59.09 1.01 7.47 0.74 9.22 0.39 10.50 0.18 11.07 - 22.11 0.47 22.58 0.71 4.43 0.07 5.21 - . 13.52 1.61 = 14.13 67.85 24.35 Ze 92.20 . . 5.47 0.19 5.66 1.61 . 4.05 0.01 5.67 Not analyzed Partially degraded asbestos or olivine fibers were weak and mechanically reduced to nonfibrous material by the other analytical techniques hence only the remaining asbestos fibrils were counted ASBESTOS EMISSIONS TRENDS- To compare the emissions properly it was found necessary to calculate the asbestos emission factors for each sample in micrograms mile Table ) The values of these factors were obtained by multiplying the weights of brake debris generated by the appropriate asbestos percents then dividing by the miles per test schedule Thus either a asbestos content or large sample gave a high factor The following observations were made Table 12 - United States Braked Motor Vehicle Population Private passenger cars R.L. Polk estimate July 1 1972 83 137 324 D.O.T. estimate July 1 1972 Trucks R.L. Polk estimate July 1 1971 18 462 287 D.O.T. estimate July 1 1972 includes 897,456 truck tractors Light { Under 6000 lb gvw 6000-10,000 12,109,000 4,952,000 10,000-14,000 10,000-14,000 125,000 Medium Heavy Buses 14,000-16,000 16,000-19,500 19,500-26,000 { O2v6e,r00303-,3030,0000 125,000 645,000 1,290,000 395,000 1,165,000 D.O.T. estimate July 1 1972 Miscellaneous motor vehicles motor cycles etc. D.O.T. estimate July 1 1972 Total motor vehicles in use D.O.T. estimate July 1 1972 96,397,000 403,000 3,787,000 121,400,000 Gross vehicle weight estimates from 1970-1971 sales data extended by this study This total includes approximately 1.5 million public vehicles 450,000 cars 920,000 trucks and 185,000 buses but does not include 190,000 Department of Defense vehicles in worldwide use Table 13 Compilation of Annual Motor Vehicle Brake Friction Material Usage Vehicle Description Amount Used No. and Unit Weight per Unit lb Passenger car Light truck Medium truck or bus Heavy truck Miscellaneous trailers etc. Front disc pads only Front drum linings only Rear drum linings only Drum linings Drum linings Drum linings Drum linings 9,660,000 axle sets 24,300,000 axle sets 32,400,000 axle sets 4,730,000 vehicle sets 670,000 vehicle sets 781,000 vehicle sets - 1.0 1.8 1.3 5.0 15.0 41.0 - Calculated from Friction Materials Standards Institute D.O.T. and Stanford Research Institute Data Total Weight lb 9,660,000 43,700,000 42,100,000 23,700,000 10,100,000 32,100,000 10,000,000 171,360,000 14 1. Asbestos emissions were higher for new friction surfaces - and decreased with use 2. The drum brake produced more asbestos emissions than the disc brake initially with the difference decreasing as the friction materials continued in use 3. Heavy abusive duty did not necessarily give a higher percent of asbestos the large amount of debris produced however gave a significant rise in asbestos emissions 4. Asbestos emissions from the brakes were found to decrease from fade or heavy stops highest to burnish to moderate braking lowest 5. For the disc pads only there was an increase in asbestos emissions with increased asbestos content in the friction material There was no such trend for the drum brake materials 6. Both the front disc pads and the drum linings of vehicle test 3 have wear comparable to that found in the other two vehicle tests yet the asbestos emissions were significantly lower Both pads and secondary linings contained brass chips which may have been in part responsible for the more complete conversion of the asbestos in the brake emissions 7. For both disc and drum brakes the surfaces sample was the largest of the three 92 the sump sample was next % and the airborne sample was the smallest % ESTIMATE FOR ASBESTOS EMISSIONS The purpose of the following discussion is to develop an estimate of total brake and clutch emissions from the United States population of motor vehicles in use on the roads and highways Inputs include all of the test results described earlier together with a supplementary data base on United States motor vehicle population and usage and on friction material usage and consumption obtained from other sources Because of the uncertainties in all of the data available emissions can only be considered as a broad range rather than as a single value with the expectation that the true average emissions for both individual vehicles and the motor vehicle population in general will be within the range of values calculated below DATA BASEBASE To calculate the asbestos emissions for all vehicles it was necessary to assemble the following data base Number of Vehicles in Use - Table 12 lists the total United States motor vehicle population as estimated by both Department of Transportation DOT National Highway Traffic Safety and Federal Highway Administration 8 and by the R. L. Polk Co. 9 The Polk census is said to be more precise because it eliminates multiple registrations of the same vehicle Polk considers that DOT estimates may be as much as 13 too high Both Polk and DOT omit military vehicles but include all other motor vehicles that are state- licensed including police cars school buses and the like Independently the General Services Administration reports that 190,000 Department of Defense vehicles are in use worldwide In addition there are 6.6 million braked trailers and 38.4 million motor vehicles with dry clutches Motor Vehicle Usage- The approximate total number of miles traveled by all United States motor vehicles was 1.249 trillion miles for 1972 according to a recent DOT estimate 8 The average annual mileage for passenger cars is 9978 miles while for trucks it is 9807 miles An attempt was made to estimate the proportion of United States driving that takes place in predominantly hilly or mountainous areas where long steep grades are common Basic data on miles driven in each state were obtained from DOT The percentage of driving that takes place in mountainous areas where abusive brake use may be necessary is estimated to be 11.5 of all driving The estimate is subjective to a large degree and may be high but no better data have been located Asbestos in Friction Materials - The data in Table 13 indicate that the total amount of asbestos contained in all of the automotive brake friction materials sold each year is calculated to be about 103 million lb which corresponds to 118 million lb used prior to grinding Two of the most knowledgeable sources 10 11 report that 90-120 million lb per year are used A report from IIT Research Institute suggests that 67 million lb are used annually in brake linings 12 A Bureau of Mines Report 13 based on 1968 data credits only 50 million lb of asbestos to automotive use a number the authors find to be much too small Ignoring the two latter values the three estimates of asbestos contained in brake friction materials range from 90-120 million lb. Using the calculated vehicle of 118 million lb and assuming a 15 grinding and drilling loss the maximum amount of asbestos incorporated in brake friction materials is taken to be 103 million lb per year A compilation of data on clutch friction materials was also made 14 Based on these data the total amount of asbestos contained in all automotive clutch friction materials sold each year is calculated to be about 4.5 million lb. AMOUNT OF FRICTION MATERIAL ACTUALLY WORNWORN For several reasons the amount of brake lining and asbestos worn away during a year is significantly less than the total amount installed on vehicles Brake linings are seldom completely worn away Due to the geometry of brake Table 14 Compilation of Calculations for Amount of Brake Friction Material Worn Away Annually Calculation Total Brake Friction Material million lb Installed weight each year Discarded on relining 25 Discarded on vehicles retired 7 million cars x 2.38 lb x 40 = 6.7 + 0 75 million light trucks ^ 5 lb ^ 40 1.5 + 0.10 million medium trucks x 15 lb x 40 = 0.6 + 0.15 million heavy trucks X 41 lb x 40 = 2.4 + miscellaneous = 0.5 Amount worn away annually 1714 1714 427 117 1170 15 systems perhaps 10 of the lining is still left on a brake when lining through occurs Linings are usually replaced in sets rather than piecemeal As a consequence of this and other actions about 25 of all brake linings are discarded at relining time Furthermore millions of vehicles are 1 retired from service each year many with brake linings that are far from worn out Perhaps the average retired vehicle has about 1/3 of its usable lining remaining or 1/3 ^ 90 + 10 = 40 of the installed weight of the lining Combining these figures the amount of brake friction material worn away each year is calculated in Table 14 Employing the same reasoning for clutches the amount of clutch material worn away is calculated to be 6.56 million lb. Summarizing the combined total of brake and clutch friction material worn away annually is 117.0 + 6.6 = 123.6 million lb. Assuming that the average asbestos content is Table 15 - Distribution Factors for Test Vehicle Simulation Test Schedule Required Airborne Atmosphere Road Dropout Disc brake New friction couple After 2632 miles After 8100 miles After 20,000 miles Drum brake New friction couple After 2632 miles After 20,000 miles Burnish _ Composite Composite Composite Burnish Composite Composite 0.04 0.07 0.06 0.06 0.01 0.02 0.02 0.85 0.91 0.93 0.93 0.54 0.72 0.79 Vehicle Retention 0.11 0.03 0.01 0.01 0.35 0.26 0.19 Table 16 - Weighting Factors for Test Vehicle Simulation Test Schedule Required Weighting Factor New friction couple Surfaces preparation Moderate braking Severe braking Renewal of friction surfaces Burnish A.B. Baseline Detroit Traffic 10 Stop Fade A.F. Baseline 0.013 0.013 0.934 0.020 0.020 Determined by difference Schedule Burnish A.B. Baseline Detroit Traffic 10 Stop Fade A.F. Baseline Table 17 - Total Asbestos Emissions Calculated from the Test Vehicle Average for the Three Vehicle Tests Friction Couple Disc brake Drum brake Clutch Disc brake Drum brake Clutch Disc brake Drum brake Clutch Disc brake Drum brake Clutch Disc brake Drum brake Clutch Asbestos Emissions mile Vehicle Vehicle Test 1 2 3 Average 16.70 59.09 - 2.23 9.22 - 2.35 1107 1107 - 100.60 22.58 - 29 61 21 . 36.35 24.43 - 4.71 2.38 - 12.75 5.50 - 79.13 146.14 - 669 669 28 - 7.21 11.67 - 1.96 1.98 ~ 0.48 0.63 - 8.82 5.03 - 3.51 0.32 - 20.09 31.39 1.11 2.97 4.52 1.11 5.19 5.73 1.11 62.80 58.15 1.11 13.27 2.94 1.11 Per Axle 40.18 62.78 - 5.94 9.04 = 10.38 11.46 - 125.60 116.30 - 26.54 5.88 ~ SeverityWeighting Factors 0.013 0.013 0.934 0.020 0.020 Total Weighted Emissions mile 0.52 0.82 0.01 0.07 0.12 0.01 9.70 10.70 1.03 2.51 2.33 0.02 0.53 0.12 0.02 28.51 Schedule Friction Couple Burnish A B. Baseline Detroit Traffic 10 Stop Fade A.F. Baseline Disc brake Drum brake Clutch Disc brake Drum brake Clutch Disc brake Drum brake Clutch Disc brake Drum brake Clutch Disc brake Drum brake Clutch Table 18 - Distribution Weighted Asbestos Emissions from the Test Vehicle Asbestos Emissions mile Vehicle Test Distribution Factors Per 1 2 3 Average Axle Dropout Airborne 16.70 59.09 - 2.23 9.22 - 2.35 11.07 - 100.60 22.58 - 29.61 5.21 - 36.35 24.43 - 4.71 2.38 - 12.75 5.50 - 79.13 146.14 - 6.69 3.28 - 7.21 11.67 - 1.96 1.98 - 0.48 0.63 - 8.82 5.03 ~ 3.51 0.32 - 20.09 31.39 1.11 2.97 4.52 1.11 5.19 5.73 EL 62.80 58.15 1.11 13.27 2.94 1.11 40.18 0.85 62.78 0.54 - 0.10 5.94 0.85 9.04 0.54 - 0.10 10.38 0.93 11.46 079 - 0.10 125.60 0.93 116.30 0.79 - 0.10 26.54 0.93 5.88 0.79 - 0.10 0.04 - 0.01 0.01 0.04 0.01 0.01 0.06 0.02 0.01 0.06 0.02 0.01 0.06 0.02 0.01 Severity- Weighting Factors 0.013 0.013 0.934 0.020 0.020 Total Weighted Emissions mile Dropout Airborne 0.44 0.02 0,44 0.01 0.00 0.00 0.06 0.00 0.07 0.00 0.00 0.00 9.02 0.58 8.45 0.21 0.10 0.01 2.33 0.15 1.84 0.04 0.00 0.00 0.49 0.03 0.10 0.00 0.00 0.00 23.34 1.05 16 17 60 by weight the amount of asbestos worn away as friction material wear debris is 74 million lb. WEIGHTING FACTORS- Two series of weighting factors were developed to handle the test vehicle data Distribution Factors - The distribution factors were calculated from the material recoveries in the shrouded and unshrouded brakes as indicated earlier Estimates were made for both disc and drum brakes from the test vehicle for the amounts of the different samples dis- tributed from the brakes These estimates were made for the Burnish schedule for the end of a complete vehicle test and for the end of all three vehicle tests For the drum brake estimates were made for up to 40,000 miles The factors are given in Table 15 Severity Weighting Factors - The weighting factors were calculated from the percentages of different braking modes for new versus burnished friction materials for severe or abusive versus moderate braking and for the renewal of friction surfaces postfade The factors are given in Table 16 ASBESTOS EMISSION FOR TEST - VEHICLES The pro- gram results were used to develop the following estimates Mile Emission emission Per Mile Asbestos Emission - The total asbestos emission for the test vehicle can be estimated from the test results given earlier and the weighting factors The calculation is summarized in Table 17. The asbestos emissions for the disc brakes drum brakes and clutch from each vehicle test were averaged and used with the Burnish A.B. Baseline Detroit Traffic 10 Stop Fade and A.F. Baseline schedules The corresponding severity factors were used to calculate the weighted emissions The sum of the weighted emissions is the total asbestos emission expected from an average vehicle Distribution The total asbestos emissions per vehicle as calculated above are not merely deposited onto the ground or entirely emitted into the atmosphere In general the asbestos emission can and will probably end up in any of three different places 1. Retained in the brake and disposed of during service 2. Deposited on the ground 3. Emitted to the atmosphere The calculation in Table 18 shows that the largest part of the asbestos emission produced is emitted from the brakes and clutch as dropout material The fate of the total asbestos emission calculated earlier for the test vehicle is shown in Table 19 Table 21 - Estimated Emissions Factors forfor TrTurcukcsks Friction Material Front drum brake Rear drum brake Clutch Light Truck 2.0 3.0 2.0 Medium Truck Bus 3.0 10.0 4.0 Heavy Truck 0 300 6.0 Table 19 - Fate of Total Asbestos Emissions from Test Vehicle Fate Percent dropout Airborne Retained in in brbarkaeke 81.9 3.7 14.4 Table 20 - Estimated Weighting Factors for Trucks Simulation Test Schedule Weighting Factor Light truck New materials Moderate braking Moderate braking Abusive braking Surface renewal Medium truck and bus New material Moderate braking Moderate braking Abusive braking Surface renewal Heavy truck New materials Moderate braking Moderate braking Abusive braking Surface renewal Burnish A.B. Baseline Detroit Traffic 10 Stop Fade A.F. Baseline Burnish A.B. Baseline Detroit Traffic 10 Stop Fade A.F. Baseline Burnish A.B. Baseline Detroit Traffic 10 Stop Fade A.F. Baseline 0.013 0.013 0.874 0.050 0.050 0.013 0.013 0.774 0.100 0.100 0100 0100 0013 0013 0674 0674 150 0150 Table 22 - Estimated Asbestos Emission per mile for Trucks VeVheihcilcele Light truck Medium truck or bus Heavy truck Asbestos EmISSION mile mile 87.51 290.72 951.12 Table 23 - Total Asbestos Emission for Trucks Vehicle Light trucks Medium trucks or buses Heavy trucks Total Asbestos Emissions lb 32,300 16.300 32.900 81.500 Table 24 - Fate of Total Asbestos Emission for Trucks Fate dropout Airborne Retained in brake Asbestos Emission 86 87.9 2.9 92 18 ASBESTOS EMISSION ESTIMATE FOR ALL VEHICLES The test vehicle results can be Extended to all passenger vehicles in the following manner Passenger Cars - The estimated total asbestos emission per year can be calculated from the following information 1. Total asbestos emission per vehicle is 28.51 mile 2. Number of miles per vehicle is 9978 3. Number of passenger vehicles is 96,400,000 From the above the estimated asbestos emission in pounds per year 28.51 48 vehicle 1 106 X 9.978X 103103 miles year 1 | X 454 % X 96.4 ^ 106 vehicles = 60,400 lb per year The distribution of the total asbestos emission calculated for the test vehicle can be determined by applying the percent distributions given earlier The fate of the 60,400 lb cal- culated above for the test vehicle shown in Table 19 Trucks and Buses - Truck brakes usually tend to operate at higher temperatures than passenger cars Thus a greater proportion of temperature use in severity weighting can be obtained by using a larger fraction of the 10 Stop Fade asbestos emission For trucks and buses the test results are arbitrarily weighted as given in Table 20 In addition to the severity factors it is necessary to estimate the total average asbestos emission for a light truck a medium truck or bus and a heavy truck The value for the test car was 28.51 mile Assuming that trucks have results proportional to the ratios of the friction material weights the asbestos emission for trucks are larger than for the test car by the factors shown in Table 21. A slightly larger factor is selected for the clutch as it is used more often in trucks than in passenger cars The estimates for the total asbestos emission per light truck medium truck or bus and heavy truck were calculated using the severity and emissions factors given in Tables 20 and 21. These results are shown in Table 22 The total asbestos emission per year for light trucks can be calculated from the following information 1. Total asbestos emission per vehicle is 87.51 mile 2. Number of miles per vehicle is 9807 3. Number oflight trucks is 17,100,000 Estimated asbestos emission in pounds per year ^ ug ^ miles 87.51 ^ 106 X 9.807 103 lb y LD mile ug year 454 X 17.1 ^ 106 vehicles = 32,300 lb per year The estimated value for the total asbestos emission from trucks and buses is shown in Table 23 The distribution factors for trucks were calculated based on the following considerations The truck drum brake is designed to be more open than the car drum brake and in many instances no splash shields are used Based on the estimates that only about 25 as much debris remains in a truck drum brake as compared with a passenger car drum brake distribution factors for trucks were estimated The distribution of the total asbestos emis- sion estimate is shown in Table 24 SUMMARY AND CONCLUSIONS The purpose of this program was to obtain asbestos emis- sion data from brakes and clutches for a vehicle during actual operation Unique emissions collectors for a disc brake drum brake and clutch were conceived designed built and installed on a vehicle The vehicle was driven through various test cycles to determine the extent and type of brake emissions generated at both low and high temperatures Typical original equipment and aftermarket friction materials for both disc and drum brakes were used in the tests Brake relines were made to simulate consumetrype practices The particulates were processed and analyzed by a combination of optical and electron microscopy Table 25 - Summary of All Brake and Clutch Emissions pounds per years Vehicle Passenger cars Light trucks Medium trucks and buses Heavy trucks Miscellaneous No. of Vehicles Total Asbestos Emissions 96,400,000 17,100,000 2,600,000 60.400 32,300 16,300 1,200,000 32,900 6.615.000 16,300 Totals 158.200 Percent of total Dropout Distribution Airborne Brake Retention 49.470 28,420 14.330 2,230 940 470 8,700 2,940 1,500 28,920 14,330 135,470 85.6 950 470 5,060 3.2 3,030 1,500 17,670 11.2 Estimated equal to medium trucks as weights of friction material used for both categories are almost equal Table 12 12 Includes motorcycles trailers etc. 19 The range of asbestos content in the brake emissions for vehicle tests 1 and 2 went from a high of 1.65 to a low of 0.03 for the 90 analyses only three were above 1.00 The overall average for vehicle test 1 was 0.40 and for vehicle test 2 was 0.25 For vehicle test 3 the range of asbestos content was from a high of 0.22 to a low of 0.003 with an overall average of 0.07 These data are comparable to those obtained in an unpublished dynamometer study 15 In none of the samples tested in this program was a 15 asbestos content found as reported by Lynch of the U.S. Public Health Service 16 To compare the generation of asbestos emission properly it was found necessary to calculate the emission factors for each sample in mile These values were obtained by multiplying the weight of generated brake debris by the appropriate asbestos percent followed by dividing by the miles per test schedule Thus either a asbestos content or a large sample gave a high factor The estimates of total emissions and their distribution for the test vehicle were obtained by employing distribution- and weighting factors These data were then extended to all passenger vehicles and trucks and buses in the United States The summary of the total asbestos emission estimates and their distribution are given in Table 25. On the average more than 99.7 of the asbestos is converted The contribu- tion to the atmosphere is 5060 lb or 3.2 of the total asbestos emission These estimates are considered to be maxi- mum values The total asbestos emission estimates and especially the airborne emissions estimate are considerably lower than the 540,000 lb estimated by IIT Research Institute 12 ACKNOWLEDGMENTS The authors wish to acknowledge the support of the Environmental Protection Agency in this work through Contract No. 68-04-0020 The authors also wish to thank the following for their various contributions R. D. Stapleton sample collection and processing R. M. Rusnak and D. G. Jones microscopy analyses P. R. Stewart fabrication of collectors H. M. Danbert vehicle preparation J. Gulvezan A. Tomala and W. R. Kee rotating seal designs C. Cowan and H. C. Morton of Bendix Automotive Control Systems Group information on vehicle testing and friction materials J. Lindsay computer program and processing C. L. Gray and W. H. Houtman of the Environmental Protection Agency suggestions made on brake emissions collectors and J. P. Leineweber and S. Spiel of Manville Research and Engineering Center asbestos analyses Special thanks go to W. M. Spurgeon Manager of the Materials and Processes Department for his encouragement and suggestions throughout the program REFERENCES 1. A. A. Hodgson Fibrous Silicates Lecture Series No. 4. Royal Institute of Chemistry London 1965 2. K. Yada Study of Chrysotile Asbestos by a High Resolution Microscope Acta Chrystallegraphica Vol 23 1967 p 704 3. G. Bayer T. A. Brown and R. D. Zumwalde Equipment and Procedures for Mounting Millipore Filters and Counting Asbestos Fibers by Phase Contrast Microscopy H.E.W. Public Health Service February 1969 4. R. E. Heffelfinger C. W. Melton and W. Henry Development of a Rapid Survey Method of Sampling and Analysis for Asbestos in Ambient Air Interim Report to National Center for Air Pollution Control July 1970 5. W. J. Nicholson A. N. Rohl and E. F. Ferrand Air Pollution in New York City Presented to Second International Air Pollution Conference Washington D. C. December 1970 6. J. Murchio private communication 1971 7. P. Leineweber private communication September 1972 8. National Highway Traffic Safety and Federal Highway Administration estimates private communication Jan. 18 1973 9. R. Polk & Co. private communication Jan. 12 1973 10. Private communication January 1973 11. Private communication January 1973 12. C. Harwood Asbestos Air Pollution Resulting From the Wear of Braking Linings Illinois Institute of Technology Research Institute April 1972 13. T. May and R. W. Lewis Mineral Facts and Prob lems Asbestos U. Bureau of Mines Bulletin 650 1970 edition 14. Private communication January 1973 15. S. Spiel Manville Research and Engineering private communication 1971 16. J. Lynch Brake Lining Decomposition Products J. Air Poll Control Assoc Vol 18 1968 No. 12 24 | This paper is subject to revision Statements and opinions advanced in papers or discussion are the authors and are his responsibility not the Society's however the paper has Society of Automotive Engineers Inc. TWO PENNSYLVANIA PENNSYLVANIA PLaza NEW YORK N 10001 been edited by S^ Efor uniform styling and format Discussion will be a with the paper if is published Transactions permission to put this paper in full or in part contact the SAE Publications Division and ye authors 20 page booklet Printed USA USA