On November 20, 1968, a gas and dust explosion occurred in the No. 9 mine in Farmington, Marion County. It caused a huge cloud of smoke and flames, and debris was thrown from the mine. While 21 miners escaped, 78 men were trapped and died. Rescue efforts were delayed until the fires were out, and the mine was initially sealed after nine days. 19 bodies were never found.

This disaster led to major changes in mine safety. A mine safety conference was held in Washington, and Congress passed the 1969 Coal Mine Health and Safety Act. This law set stricter safety rules, including banning work under unsafe conditions and giving federal inspectors the power to close dangerous mines. The disaster also contributed to the removal of Tony Boyle, the president of the United Mine Workers, who had defended the company after the explosion.