Finer Coal Dust Changes Formula for Preventing Explosions

NIOSH on Aug. 21 said more inert material should be spread in the intake airways of underground bituminous coal mines because coal dust found in those mines today is much finer, and thus more explosive, than in mines of the 1920s.

The composition of rock dust that is spread inside intake and return airways of underground bituminous coal mines to reduce the explosive potential of coal dust should be increased because new tests have shown the coal dust in today's mines is typically finer, and therefore more explosive, than it was decades ago. NIOSH announced the findings yesterday in a publication seeking comments by Sept. 30.

Rock dust is the primary method of preventing explosions in these mines. Current MSHA regulations require that intake airways contain at least 65 percent incombustible content and return airways contain at least 80 percent, the latter being higher because finer coal dust tends to collect there, NIOSH said. The regulations were based on a 1920s survey of coal dust particle size and explosion tests conducted in the U.S. Bureau of Mines' Bruceton Experimental Mine, the agency said. But now, NIOSH and MSHA have done a joint survey showing the coal dust found in mines today is much finer than in mines of the 1920s, "presumably due to increased automation and a greater reliance on mining machinery," according to NIOSH.

So the agency on Aug. 21 recommended a new standard of 80 percent incombustible content for intake airways, as well. The current requirement of 80 percent in return airways does not need to be changed, it said.

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