Widespread explosions in coal mines can be prevented if rock dust of suitable size and composition is applied effectively within two or three cuts of face; distance between end of rock dusting and face should never exceed 80 feet. Water should be used on cutter bar of mining machines, and coal piles and should not only be wetted after blasting but kept wet during landing.

This paper describing the milling methods at the Walkermine concentrator, Plumas County, Calif., is one of a series being prepared by the United States Bureau of Mines on milling methods and costs in the various mining districts throughout the United States