An explosion at the Massey Energy Co. mine in Montcoal, West Virginia, killed at least 25 miners. The cause of the explosion had not been determined as rescuers worked Tuesday to bore ventilation holes into the Upper Big Branch Mine. This is a chronological list of notable coal mine accidents in the United States over the last century. The list is not all-inclusive. * December 6, 1907 -- Worst coal mine disaster in U.S. history: 362 miners are killed in an explosion at the Monongah Nos. 6 and 8 Coal Mines in Monongah, West Virginia.