On January 4, 1989, retreat mining in the 001 Section of the CV-2 mine was advancing.  As part of this operation, miners extracted coal from the No. 5 pillar, and then from the No. 4 pillar.  At about 2:40 p.m. as final cuts were being made to the No. 4 pillar, a sudden roof fall occurred.

Three miners died in the fall.

MSHA investigators determined that the roof of the immediate fall area had contained an undetected "horseback" - a horse-back shaped mass of stone in the roof that is bordered by discontinuities.

While one edge of the horseback had rested on the outby corner of the No. 5 coal pillar, the other edge had rested on the No. 4 pillar.  Once the critical outby corner of the No. 5 pillar was removed in violation of the roof control plan, and final recovery of the No. 4 pillar was conducted, the unsupported horseback collapsed.

Another factor contributing to the disaster was missing posts; only five of fifteen timbers required by the roof control plan had been installed.  The severity of the accident was also compounded by a failure to restrict persons from a hazardous location during retreat mining.

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