Document 0bq6w760OjzrLVgbjmw3RE9d

c. KING'S FLOATS ASUESTOS DOST The firot inhalation experiment oonduotcd at tho Saranao Laboratory with asbestos dust was begun in 1928. Animals inhaled the dust for periods up to 33 months. Some guinea pigs with 6 and 9 months' exposure lived for an additional three yoars after cessation of tholr exposuro. A preliminary roport^^ presented observations aftor 29 months of exposure. At that time observations oovered a period, of only 2-l/4 years end the conclusions as to tho ultimate effeots of inhalod asbestos dust wore provisional. Those conclusions aro substantiated by results of tho completed study, which is reported as follows. Composition and Atmospheric Concentration of the Dust. The dusting material, a commercial varloty of asbestos lenown as King's floats, was oomposod of short . ..... fibors, ranging in length from 1 milllmoter to 1 micron or loss, and of particles which also varied in also. It was obtained from the Thetford, Quoboc plant of tho Acbustoa Corporation of Amerioa end analysos (tables 2 and 3) roveol that the amount of fibrous ohryaotlle was only 14 per cent, a rathor low value. Impingor samples talcon soon aftor tho experiment was started indicated that the dust concentration was at first quite low, the average dust count being only 6.0 million particlos per for cublo foot of elr by the standard light-field technique and 0.8 milllon/partlclea and fibers groator than 10 micrana. After tho inhalation experiment had boon, under * ' way for about two years, tho speed of the rotating paddle in tho dusting maohino was inoroasod and for tho remaining 10 months of tho experiment considerably moro . dust was dispersed into the atmouphere. Tho average dust count of irapinger samples collected after this change was 63.7 million by the usual light-field mothod and -- 1.6 million for particlos and fibers larger than 10 microns. It is probabl-', how- evor, that tho true values of the dust concentration wore higher than tho counts given in this paragraph. Tho impingor samples for tho King's floats experiment woro 9- - f.