Document NeLeMmdOL1gDROrBOo7jVQLnp

FEB-02-2005 08:36 SflE CUSTOMER SALES 724 776 0002 P.06 4 largest observed asbestos fiber in the test filter (0.13 jum in diameter and over 1.2 fim long) was about the same size as was found on the background sample. The similar, low fiber content of both background and test filters precluded a fiber size distribution estimate. However, it appeared that the quantity of the larger asbestos fibers on the test filter was no greater than that of the background filter. This supports the observation from the lining wear visualiza tion tests that normal brake wear degrades most of the as bestos fibers. A brake lining grade of asbestos appears on the TEM as in Pig. 4. The fiber bundles are composed of strong, but weakly adhering fibrils of about 0.03 pm (roughly 1 /tin) diameter. Mechanical action causes the larger fibers to "open" into smaller fibers or even fibrils, as illustrated in Fig. 5. Con trast these "raw material" fibers with one of the larger fibers (Fig. 6) and one of the more typical fibrils (Fig. 7) from the "normal use" test filter. The similar, low fiber content of both background and test filters required clarification to permit an asbestos fiber count, thus providing more accurate fiber mass determination, but obscuring the actual fiber size distribution. Therefore, the calculations of fiber concentration (Table 1) were expressed as asbestos mass per unit mass oflining wear dust and asbestos mass per unit mass oflining worn. Asbestos fiber concentra tion in the ambient air (background) and in the brake exhaust air (test) was calculated in units of nanograms (ng s 10"^ grains) per cubic meter of air. However, the actual asbestos emissions from brake usage would be diluted substantially through mix ing. The asbestos concentration in urban air due to brake usage was estimated based upon existing automotive exhaust lead dilution data. These calculations appear in Appendix C. All the test results in Table 1 have been reported as ten times the calculated test values to allow for possible losses in Fig. 4 - TEM image of chrysotile asbestos fibers Fig. 6 - TEM image of fibci bundle on "normal use" filter Fig. 5 TEM image of partially opened fiber bundles Fig. 7 - TEM imafie offibril on "normal uce" filter