The immediate roof of the Stillhouse No. 1 Mine was composed of four to fifteen feet of bone - a hard coal-like substance often found above, below or between layers of relatively pure coal.

During the evening of December 3, 1981, the afternoon crew of the Stillhouse Run No. 1 Mine worked the operation's No. 2 entry.  Their activities included advancing the face of the entry, excavating the left crosscut to a depth of about 18 feet, and making a "widening cut" in the right crosscut in preparation for mining in that area.

At about 9:20 p.m. the mining machine was shut down to reposition previously installed posts and to position the roof bolting machine near the left side of the left crosscut.  Soon after, the roof collapsed, killing three miners and seriously injuring a fourth miner.

After the accident, MSHA investigators identified hairline roof cracks and separations in numerous locations throughout the mine, and a large separation within the accident area.  In addition, undisturbed bone recovered from the accident area indicated that fracture planes had extended to the bottom of the bone roof along the edge of the widening cut.

However, neither cracks nor separations had been evident in the accident area before the fall, according to interviews conducted with miners after the fall.  Because of these statements and other evidence, MSHA investigators attributed the fall to undetected fractures located in the roof near the right rib of the No. 2 entry, where the widening cut had been mined.

MSHA investigators also determined that only about 50 percent of roof support rods in the No. 2 entry had been grouted throughout 80 percent of their lengths, as required by the roof control plan.  Such inadequate grouting may have also contributed to the fall.

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