On December 6, 1907, a massive explosion at the Fairmont Coal Company’s No. 6 and 8 mines in Monongah, Marion County, killed at least 361 men, making it the worst mining disaster in U.S. history. The exact cause was never proven, but it likely involved gas and coal dust ignited by a spark from a train wreck, blasting, or open flame.

Most of the victims were recent immigrants from Italy, Hungary, and Russia. With no trained rescue teams, miners from nearby states came to help. Some victims were boys as young as eight. The real death toll may have been higher since the mine's records were destroyed.

That same month, three more deadly mining accidents happened, and 1907 became the deadliest year in U.S. mining history with over 3,200 deaths. Unsafe practices like using open flames and poor explosives were common.

Public outrage led to changes. In 1910, the U.S. Bureau of Mines was created to improve mine safety. In 2009, Congress named December 6 as National Miners Day to honor those who lost their lives.