The Mine Safety and Health Administration (MSHA) on Dec. 6 imposed a fine of $10,825,368, the largest in agency history, and 369 citations following its investigation into the April 2010 explosion at the Upper Big Branch-South Mine, which was operated by Performance Coal Co., a subsidiary of Massey Energy Co.

The investigation followed an explosion that killed 29 miners and injured two. It’s being called “the worst U.S. coal mining disaster in 40 years.”

A report concludes that Massey’s corporate culture was the root cause of the tragedy. MSHA has issued Massey and PCC 369 citations and orders, including for an unprecedented 21 flagrant violations, which carry the most serious civil penalties available under the law.