Document XRw9wp1dmgj1Dm9B94J8w3KOJ

FILE NAME Brakes BRK DATE 1972 April DOC BRK039 DOCUMENT DESCRIPTION Report - IIT Research Institute - Asbestos Air Pollution Resulting from the Wear of Brake Linings APRIL Oboe elie ASBESTOS AIR POLLUTION RESULTING FROM THE WEAR OF BRAKE LININGS By Colin F. Harwood Ph.D. ABSTRACT Asbestos containing brake source of ambient air asbestos linings have been cited as a pollution This paper reviews the suggestion and an estimate is presented which indicates. that the asbestos emission from brake linings is significant The ways in which this emission may be reduced or eliminated are briefly reviewed IIT RESEARCH INSTITUTE 10 West 35th Street Chicago Illinois 60616 11T RESEARCH INSTITUTE 65 ASBESTOS AIR POLLUTION RESULTING FROM THE WEAR OF BRAKE LININGS INTRODUCTION Recent interest in asbestos and the realization of its health hazard have raised the question of the extent to which people are exposed to asbestos Measurements have been made on on a occupational basis urban background levels and it has been shown that small but definite concentrations are to be found in areas quite remote from any apparent source Since virtually every motor vehicles carries several pounds of asbestos contained in its brake linings and since these are worn away to some degree every time the brakes are applied then it is reasonable to expect that they could present a significant emission source This is especially acceptable when one considers the 100 million or so vehicles on the nations roads The paper investigates the possible extent of such emissions and presents an estimate of the contribution to urban asbestos concentrations Possible means of reducing such emissions by use of an alternative or sealing the system are briefly reviewed The Extent of the Emission The best information available at the present time 2 indicates that the percentage of asbestos contained in the dust normally emitted from brake linings is of the order of % However under conditions of severe breaking this may rise to 15 The average brake friction material contains of the order of 50 asbestos thus an explanation is necessary to account for the discrepancy between the measured and theoretical values The most likely explanation results from the known facts with regard to heat generated at friction surfaces The work of Bowden and Tabor has shown that when two surfaces are placed together the contact area is dramatically less than the apparent area IIT RESEARCH INSTITUTE 66 This means that very large energy transfer takes place at these contact points and extremely high temperatures are reached In the case of brake linings some evidence of these temperatures has been generated in unpublished work by the General Motors Company In this study a small hole was cut through a brake shoe and the radiation collected from the ex- posed shoe surface was monitored The results suggested that under light braking temperatures of the order of 800-900 were found while during heavy braking the temperature reached 1700-1800 The significance of this data to the present case is 5 give that it is known that asbestos decomposes above 500 to give forsterite SiO talc si 10 OH 2 and water vapor Acceptance of the value of % of asbestos emitted allows an estimate to be made of the effect of this emission on the quality of the atmosphere Estimation of Urban Concentrations of Asbestos From Brakes Assumptions a There are approximately 100 million motor vehicles b Motor vehicles have an approximate average weight of 4 lbs of friction material when new of which 50 is asbestos C. The average motor vehicle will require replacement of the brakes after three years of use at which time they will have lost 50 of their weight by abrasion a The dust emitted will contain % of asbestos fibers e Of the wear dust 80 is emitted and 20 is lodged within the system The AAA cluding claims there are 109,000,000 licenced vehicles in90,000,000 passenger vehicles and 19,000,000 trucks IT RESEARCH INSTITUTE 67 ae ee Calculation The total weight of brake linings in use is 100,000,000 ^ 2000 4 = 200,000 Tons The quantity worn off these linings per year follows from the assumptions made in 1 200,000 x X 50 200,000 = Tons as 3 100 6 This wear dust contains % asbestos hence emission is 200,000 200,000 200,000 6 1 2000 See = 100 6 Tons Allowing for the fact that emission is thus 20 is not emitted the total 2000 80 1600 _ _ _* 7 Tons 6 100 6 270 Effect on the Atmosphere There are no facts relating directly to asbestos on '- which one may judge the effecotf these emissions on urban air However there has been a considerable amount of study done on the diffusion of other materials from automobiles particularly lead and carbon monoxide At a recent ACS Symposium in Minneapolis evidence lead emission at 0.01 was presented which placed min Thule Alaska and the 2.5 level for min New York City Next to busy highways a level in excess of 50 gmay well be possible In the light of this data the value of 2 mfor average urban air conditions suggested by GM4 , seems eminently reasonable Considering that 1.25 x 105 tons of lead are emitted in total from automobiles then the following factor is used Avg Conc asbestos in city air from automobiles _ Quantity of asbestos emitted 2 mcity air 105 1.25 1.25 1.25 x 105 tons Pb from cars Applying this figure to the present case and assuming that 200 tons are emitted in city areas then we get that IT RESEARCH INSTITUTE 68 The avg conc 5 200 ^ 1.25 x 10 Se 3.2 x 10-3 m or ...3.2 x m3 A similar result is obtained using the dispersion for carbon monoxide However the values for lead are since it is a particulate emission rather than a gas factor preferred The Significance of This Value The question of whether asbestos containing brake linings constitute a significant source of ambient air background asbestos levels can now be considered Firstly it is pertinent to review the available evidence on asbestos levels in ambient air Perhaps the most date information is reported in a recent paper by Thompson and Mmorga n EPA m0. 5-15 found of the : Their data suggests that values are appropriate to in nonurban sites urban They sites while 0.1 give a figure of 0.01 0.5-15 0.5-15 is to be ng for remote sites with The the California State School of Public Health Department Health Berkeley in collaboration California have tested values ambient of 0.06 mf or air asbestos Their results in remote sites and 3 ng suggest near near a source Nicholson and Rohl of the Mt. Sinai School of Medicine have also been active in the measurement of asbestos in urban ambient air The revealed that 33 contained 1.0-5.0 analysis of a large number of samples of samples contained 0-0.9 mth e mm and 10 contained 5-20 has , 55 and a few were in excess of this All of the results be regarded the are not workers have been at pains to point out that to be considered preliminary Thus they should as final definite figures but rather as good IT RESEARCH INSTITUTE 69 considered preliminary findings The similarity of the figures reported by the various workers does suggest that at least an order of magnitude has been established Consider now the estimate of 3.2 mcalculated pre- viously as the contribution from asbestos it should be stated that this figure is a brake linings Firstly conservative estimate and allowance has been made for the many factors which could re- duce this figure the factor for the Secondly diffusion although of lead there is no reason to it should be realized doubt that this figure is an average Consequently much higher value for the whole of the city air concentrations are to be expected in certain areas of high brake usage For example near inter- sections tollbooths etc. In the light of the evidence here presented conclude that asbestos emitted from brake linings one may must be a _ major contributing factor in the overall ambient air concen- tration Further work is necessary to establish more definitely the major contributors to urban asbestos concentration levels It is not possible to state with assurance how much these low concentrations of asbestos constitute a threat to the health of the general public Medical evidence and opinion divergent on this issue However asbestos has been hazardous substance by the EPA and as such it should is widely rated as a be treated with due respect Emissions should be reduced or curbed wherever this is possible To this end it is worth briefly reviewing how this may be achieved 1 TECHNOLOGY OF ELIMINATING EMISSIONS The emission of asbestos to the atmosphere from asbestos | containing brakes could be prevented in two ways its use could be banned altogether or the brakes could be sealed In the former case an alternate would have to be found IIT RESEARCH INSTITUTE 70 Alternatives to Asbestos have For a replacement to fulfill a list to of be as suitable as asbestos desirable features as it would fi Resist high temperatures without degradation or loss of frictional properties fi Combine excellent friction characteristics without severe abrasion fi Provide great strength - asbestos fibers have a greater tensile strength than steel and yet are more flexible fi Have relative economy Of the materials which have been considered sintered metal with ceramic ansd fiberglass have been the most likely candi- dates thus far Sintered Metal - This material has been used and indeed has the desirable quality of being free this reason it is still used in some racing cars However it has several dis- advantages It tends to be noisy and brake screetch is a problem They suffer from what is known in the trade as morning sickness this means that the first stop is very severe or that the cold friction is high Wear is higher than with asbestos and thus the brakes have to be replaced more frequently Replacing the brakes is more difficult since all brakes are honed to fit the drum material Honing metal is more difficult than asbestos friction Ceramic Metal Cermets ~ A sintered metal and ceramic composition has been developed and tried Its use at this time seems to be restricted to the clutches on heavy vehicles tractors etc. in these cases it is usual to use buttons of the material rather than a complete annulus Although to a lesser degree it suffers from the same complaints as sintered metal with respect to noise wear and severe first stop and in addition it is relatively expensive However IIT RESEARCH INSTITUTE 71 * , its fade characteristics have led extensive testing For example metal at the Thunderbird the Ford Motor Company put inserts of ceramic position of maximum brake wear on their 1958 The concept was abandoned reportedly due to uneven braking leading to a directional pull when braking Fiberglass - Attempts to use fiberglass asbestos have been attempted since 1938. So instead far no of design has met the exacting standards required As with the other materials the first stop is harsh Apparently the design is better for disc brakes than drums A problem is the sensitivity of the brake to moisture Corning are undertaking development research in this area They are very guarded with regard to the status of their work but state that they are actively engaged in developing a product To date no vehicles are known to employ fiberglass in their brake friction product Sealed Systems Sealed systems have been seriously considered Normally cars rely on air cooling and the movement of air round the brake caused by the motion of the car However with high performance cars more cooling is required This is achieved in a simple manner by fabricating a superstructure which scoops up air and directs it inside the brake drum If a filter were added on the exiting side this would cause a substantial reduction in emissions A more elaborate design which has been used is to liquid cool the brake system This enables the braking system to be completely sealed and thus no emission are possible The one problem area with this design extremely reliable However is that the with a well oil seals must be designed system problems due to overheating could be largely eliminated IIT RESEARCH INSTITUTE 72 ae CONCLUSIONS An estimate has been made of the asbestos concentrations to be found in urban air resulting from the use of asbestos containing brake materials The results indicate that brake use may well constitute a major source of asbestos background levels The quantity in comparison to occupational levels is extremely low A time weighted average occupational ex- posure level greater than significance of 5 cc would be of the order of 100,000 times a background level of 3.0 mThe medical of these results is not known with any certainty At the present time no alternative to asbestos ing friction products is developed to the stage of finesse required by the industrIyt is difficult to believe that modern technology cannot overcome the problems presented by the use of alternates The use of sealed brake units is a second possibility Again there do not seem to be any insurmountable cal problems but no information is available as and time factors technologi- to the cost T RESEARCH INSTITUTE 73 REFERENCES Lynch Jr. et al J. Air Poll Control Assoc 18 12 824 1968 Unpublished Study Referred to by Spiel & Leinweber Res 2 166 1969 Env Bowden F.P. and of Solids Pub Tabor D. The Oxford London Friction 1950 and Lubrication General Motors private communication Bowen and Tuttle Geol Soc America Bull 60 439 1949 . Outlook Report on ACS National Meeting in Minneapolis 1969 Environmental Science and Engineering 3 529 1969 Thompson R.J. and Morgan G.B. The Determination of Asbestos in Ambient Air Int Sym on Indentification & Measurement of Environmental Pollutants Ottawa Canada e June 1971 Nicholson W.J. and Rohl New York City presented Air Congress Washington A. Asbestos Air Pollution in at Second International Clean D.C. December 1970 HIT RESEARCH INSTITUTE 74 ni ee mn