By December 11, 1985, miners had finished developing a 150-foot-long slant in the No. 2 Slope Mine, an anthracite operation.  This slant was located off the first miner heading at the No. 9 breast.

Pillaring in the slant led to a 75 foot by 75 foot void, which had been excavated.  However, unlike the mine's other pillared slants that had been connected by back entries to previously mined areas that acted as bleeder systems, this void remained poorly ventilated and without a bleeder system.

At about 2:00 p.m., miners in the No. 2 Slope fired explosives in the solid coal near the edge of the void and on top of rocks in the slant.  Immediately after, a methane explosion occurred.  This explosion killed three miners, all of whom had been positioned approximately 115 feet from and in-line with the charged shots.  A fourth miner sustained serious injuries, and a fifth miner remained uninjured.

MSHA investigators determined that the volume and velocity of air required to ventilate the slant off the No. 9 breast of the first miner heading had been insufficient to dilute, render harmless and carry away methane.  The resulting explosive methane-air mixture was ignited by the detonation of explosives in the slant.

Other contributing causes to the disaster included a failure to conduct methane testing before detonating explosives, the lack of bleeders off the No. 9 breast, and a failure to clear miners from the detonation area.

Source:
	Historical Summary of Mine Disasters in the United States - Volume II