Health and Safety

9 questions and answers on chrysotile and health

• Question 8

  Asbestos friction materials: What is the contribution to the general environment resulting from the use of asbestos in friction materials?

  Answer:

  Asbestos has been a major constituent of automotive friction materials for more than 70 years, where the presence of mostly chrysotile asbestos (from 25% to 65% by weight) imparts strength, flexibility, heat resistance to brake linings, in addition to friction and wear properties.

  Comprehensive investigations conducted with the support of the U.S. EPA have shown that on the average, more than 99.7% of the asbestos emitted as a result of wear and abrasion has been converted into other products such as forsterite, a material which has been found non-carcinogenic in animals. Furthermore, it has been determined that such asbestos (less than 1%) as may be present in wear debris consists predominantly of very short (0.3 µ) fibres.

  Thus, the emission of free fibres resulting from brake lining wear is a negligible health factor in urban air pollution. Indeed, recent estimates of air concentrations of asbestos resulting from vehicular brakes in large U.S. cities range from 0.051 ng/m³ (Rochester, NY) to 0.258 ng/m³ (Los Angeles, CA). If a conversion factor of 30 fibres measured optically per nanogram of asbestos used, the values for Los Angeles would be 7.74f/M³ or 0.000007 f/cc.

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  References for Question 8:

  Lynch JR (1968). Journal of the Air Pollution Control Association. 18(12):824-826

  This study by investigators of the U.S. Department of Health, Education and Welfare, Public Health Service (Cincinnati) provides evidence from analysis of dust obtained from inside brake drums removed for brake relining, and also from laboratory experiments devised to permit sampling decomposition products of the lining under operating conditions. The authors conclude: "Only a very small proportion of the asbestos worn from brake linings is released as free fibre; the remainder is converted into some other mineral as a result of the extreme temperatures generated at small spots on the lining surface. Thus, although urban air contains a few free fibres as a result of brake lining wear, they represent a very small proportion of the total asbestos used in the manufacture of brakes".

  Jacko MG, DuCharme RT, and Somers JH (1973). Society of Automotive Engineers, Reprint # 730548:1813-1831

  In this report by scientists from the Bendix Corporation and the U.S. EPA, the authors state that on the average, more than 99.7% of the asbestos during vehicle operation is trapped or emitted as olivine or forsterite particles.

  Jaffrey S (1990). Annals of Occupational Health. 34:529-534

  Data in the U.K. have been obtained from situations of highly intensive vehicular traffic (City of London), indicating that the use of asbestos in such applications causes no measurable contribution to urban environmental asbestos air concentrations. The asbestos fibre counts presumably released from vehicular traffic at two very busy road junctions in the Greater London Area (Motorway #1 - North Circular Road and Euston Underpass) were from 0.0002 to 0.0004 f/ml.