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1751495 
Technical Report 
Frictional Ignition with Coal Mining Bits 
Courtney, WG 
1990 
NIOSH/00202915 
S 
9251 
Studies on the frictional ignition of a methane/air environment resulting from coal mining bits cutting into sandstone were reviewed and the effectiveness of preventative techniques was considered. Six laboratory studies using water sprays with four rectangular bits and two conical bits were conducted. A field study using conical bits and back sprays mounted on the wet Simmons Rand 265 continuous mining machine was also performed. Rectangular bits included the following: Kennametal K-100, Carmet-TC3, AMS THRU, and Hydra Tools HP74ISR. Conical bits included GTE, antiignition modified cutter drum for Simmons Rand 265 continuous mining machine, and Kennametal K-178DC. Frictional ignition involved worn and flattened bit tips and most commonly steel tips as opposed to tungsten carbide tips. The risk of ignition was reduced through use of a mushroom shaped tungsten carbide bit tip and increased bit clearance angle. This laboratory finding was verified by field testing. Lowered bit velocities did not significantly decrease the risk of ignition within a practical range of velocities. Risk was reduced in the case of worn bits through use of a water spray nozzle directed at the hot streak on the sandstone surface; in general, back sprays were associated with reduced risks for all bits. Scheduled replacement of worn bits with consideration of the employed remedial technique was advised. 
DCN-202756; Workplace studies; Laboratory testing; Mining equipment; Coal mining; Mining industry; Explosion prevention; Equipment design; Equipment reliability; Explosive hazards