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Float dust deposits in return airways in American coal mines.

Kawenski-EM; Murphy-EM; Stahl-RW
Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, IC 8150, 1963 Jan; :1-20
Float dust deposits in return airways in bituminous coal and lignite mines present a special explosion hazard. Research is in progress at the Bureau of Mines experimental coal mine to evaluate the degree of the hazard and to develop measures for preventing dissemination of dust into the ventilating air current. To determine the extent of this hazard prevailing in operating coal mines, 711 dust samples were collected in 50 mines located in the major coal fields of the United States. The mean quantity of coal and the incombustible content of the dust in the samples were determined. The term "float dust" is used to designate particles smaller than 74 microns in diameter (particles passing a No. 200 sieve) which have settled from the air current. Dust usually found in roadways and in working places is coarser than float dust, and is termed "coarse dust" (particles passing a No. 20 sieve). Variations in amount and incombustible content of coarse dust in a midwestern mine were studied previously. The mean quantity of fine coal or float dust on the mine surfaces in the return airways is equivalent to 0.02 ounce per cubic foot of entry volume; the respective parts on the floor and rib-roof surfaces are 73 and 27 percent. The mean incombustible content of the float dust in return airways is 89 percent. Although this is high, 20 percent of the skim and 46 percent of the I-inch floor samples contained less than 65 percent incombustible content. In belt entries, 7 of 10 samples collected contained less than 65 percent incombustible content. Preliminary results from research on the explosion hazard indicate that the quantity of the float-coal dust is a primary factor affecting the incombustible requirement for arresting an explosion. The hazard might not be neutralized by maintaining 65 percent incombustible content as provided in the Federal Mine Safety Code.
Mining-industry; Underground-mining; Coal-dust; Explosion-prevention; Explosions; Explosive-dusts; Explosive-atmospheres
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Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, IC 8150