Document ZBaD5z1Dy7JwKa8r7nVbyGkOV

-5exposure is shown to he at a level of 1/3 of the TLV, and corresponds to a "low" dust category. (c) Laboratory investigation It is, at first sight, surprising that the exposure to asbestos is as low as found, in view of the quantity of asbestos present in the original material of the brake linings. Comparison of the fibre proportions in brake lining material and brake drum or air-borne dust (Table 4) shows that in the latter, the percentage of fibres is greatly reduoed. The analyses of the brake drum dust samples confirm a very low asbestos content. These findings suggest that during usage, the material undergoes ohanges in physioal and/or chemical form. Enquiries from researoh workers in UK and USA indicate that this is a finding which has been observed elsewhere, and current thought is that during braking, high point contact temperatures are reached. As a result, thermal deconqiosition of chrysotile asbestos takes place, producing an amorphous, non-fibrous magnesium silicate. Under very extreme operating conditions, the binder may. decompose and release part of the asbestos as free fibre, but such circumstances would be most unusual. (d) Conclusions On the environmental and analytical evidence obtained, it does not appear that a significant hazard to health should occur during brake drum blow-out in a typical Dealer Passenger Car Repair Shop. It would be helpful, however, for ... clinical 8006 1207 HFM - 005793