An explosion tore through a West Virginia underground coal mine Monday afternoon, killing 25 miners and leaving four missing. The blast occurred at Massey Energy Co.’s Upper Big Branch mine, about 30 miles south of Charleston, operated by Performance Coal Co. Ambulances rushed to the site immediately after reports of an accident surfaced. The large mine produced about 1.2 million tons of coal in 2009, the Associated Press reports, and has about 200 employees. Monday’s blast isn’t the first incident of its kind to strike the mine: In 1998, a man was killed at the site when bags of cement mix fell on him, and in 2001, a worker died when a portion of a roof collapsed on him. Last year, Massey Energy was fined $4.2 million in criminal and civil charges, ABC News reports, after confessing to "willfully violating mandatory safety standards that led to the deaths of two miners."