Document 5m8470Mo0Xo2LZoe0qJnYJ3e

distribution. Free chrysotile liber bundles and fibrils vere observed In ell ten samples (Fie. 1). Selected area electron diffraction analysis of representative fibers deconstrated the preservation of the cbrysoiile structure (Figs. 2A t B). Some patterns displayed arcuate reflections suggestive of interfibril rotation and intrafibril displace ment (Figs. 2A t B). Occasionally, fibers were observed without charac teristic chrysotlle morphology, with mottled surfaces end obliterated fibrils, indicating partial or complete rccrystallizatlon. Electron diffraction patterns obtained from these particles displayed polycrystal line characteristics of multiple random reflections or Debye-Scherrer rings rather than the distinctive single fiber chrysotlle pattern (Fig. 2B). Microcbenical analysis with a probe technique on the unaltered fibers showed them to possess the usual Mg'Si ratio of chrysotlle (rig. 3). In addition to free chrysotlle fiber bundles_and fibrils, chrysotlle vas also frequently observed projecting from the margins of binder fragments Free Bsbcstos fibers present in the decomposed lining dusts were sired at 42,000X magnification. The results, seen m Table 13, show that most fibers are too small to be seen by optical cicroscopy; almost all of them are shorter than 0.4|jn in length; virtually all are of respirable size. Hatch (1970) in reporting on optical fiber counts obtained from brake cleaning operations with compressed air jet, found th8t 945, of the fibers fell in the 2-5pm length category, while only 67, were longer than Spit. Jacko and DuCharoe (1973) made size distribution measurements of asbestos fibers in brake dusts generated during dyna mometer tests, using both optical end electron microscopy. They fannd, at magnifications of 22.000X, that 30". of the fibers vere from 0.25jn to 0.50(jnj in length and that G05 vere longer than 0.50^. Sore dis crepancies betveen our data and those of Jacko and DuCrame cay be 8005 1874 PRODUCED BY FORD