Document NGz8NG0EOjL6xMzJ4dp5r1dRg

-5 tad filter say be sees in Figure 3. A central collection cite in the test grid vac need for the "breakla teat" tad the final "high tsnperature" test. 8a^ples of the three pairc of filters (breakin, nonal use, and high temperature use) were subjected to a clarification process involving lov temperature ashing to oxidize all organic notarial and nechanical action to separate the particles. Ibis assures aaTimm detectability of asbestos fiber (2). RESULTS AND DISCUSSION Transmission electron microscopy at i0,000 magnification vas used in the search for fibers. At this magnification the ultimate fibrils appear to be ! above one millimeter (O.OkO inch) in diameter. (Juntity, length, and apparent diameter seasuresents provided data for calculation of asbestos fiber mass per ur.it oi i'ilter area. Coupled vlth dimension, mass, and flow determinations from the dynamometer tests, this data vas used to calculate the emitted asbestos fiber concentration in the collected vear dust, in the cooling air stream, and from the brake fining worn, lhe size distribution of collected fibers vas not determined by this method, since the clarification process involved sufficient mechanical action to reduce most fiber bundles to the ultimate fibril size. Additional saaples of the "normal use" test filters vere examined on the TEM vithout recourse to the clarification process, in an effort to determine the asbestos fiber size distribution. Roughly 10 of the asbestos fiber vas visible on the background sample, based on the results from, corres ponding saaples after clarification. The largest Observed fiber bundle vas .0C.C is diaseter ar.d over 1.1 um long. A sinilir direct mi search zi the "normal use" test filter revealed about 2$ of the asbestos fibers Observed after clarification. This reduced percentage of virlble fiber vas attributed to the greater concentration of Obscuring matter in the test filter. However, the largest Observed asbestos fiber in the test filter (0.13 l in diameter and over ' 1.2 tui long) vas about the seme size as vas found on the background sa^le.