Document DDLGR7rMyE8B9zp3YZRqqL464

3 1 fiber/ml (1,000,000 fibers/m ) was found. Much larger numbers of shorter fibers would simultaneously be inhaled. During the beveling of truck brake shoes on s grinding machine, very high concentrations of fibers were found in the vicinity of the operator. The average of five air samples was about 37 fibers/ml. Area samples, taken up to 30 feet away from this operation, demonstrated the presence of airborne fibers. It wbs of interest to note that, at the time of this sampling, from 8-15 other garage mechanics were working within this perimeter and wore exposed to asbestos. liber levels for other kinds of operations st the truck garage are given in Table IV. Boillat and Lob (1973) hsve reported fiber concentrations measured during ) ^^puncbing^holes for rivets and grinding. They found values ranging from V^ 0.3 to 29.2 fibers/ml; four of the nine values exceeded 5 fibers/ml. A comparison of fiber levels visible by light microscopy and electron microscopy In the ten brake drum dust samples examined, it was found that asbestos fibers shorter than 0.4pr predominated (Table II). The OSKA. Asbestos Standard does not require that short fibers (.< 5pm in length) be counted or controlled. This oversight msy have considerable biological signifi cance in that small chrysotile fibers readily produce asbestos disease (Bolt, Mills, and Young, 1964, 1965; Davis, 1965; Pott, Buth, and Friedrichs, 1972; Wagner, Berry and Timbrell, 1973; Hilscher et^ eT., 1970). Attention has recently been again called to the potential importance of this question (Bouhuys, 1975). There is little published infoimation on the numbers of, and sizes of, subnicroscopic asbestos fibers in occupational exposures. The present PRODUCED BY FORD 8005 1878