The Upper Big Branch Mine disaster occurred on April 5, 2010 roughly 1,000 feet (300 m) underground in Raleigh County, West Virginia at Massey Energy's Upper Big Branch coal mine located in Montcoal. Twenty-nine out of thirty-one miners at the site were killed. The coal dust explosion occurred at 3:27 pm. The accident was the worst in the United States since 1970, when 38 miners were killed at Finley Coal Company's No. 15 and 16 mines in Hyden, Kentucky. A state funded independent investigation later found Massey Energy directly responsible for the blast.The Mine Safety and Health Administration (MSHA) released its final report on December 6, 2011, concluding that flagrant safety violations contributed to the explosion. It issued 369 citations at that time, assessing $10.8 million in penalties. Alpha Natural Resources, which had bought Massey Energy in 2011, settled its corporate criminal liabilities with the U.S. Attorney for $209 million. Investigation of possible personal criminal liability continues, with one former superintendent, Gary May, pleading guilty in March 2012, and "confess[ing] to conspiring to 'impede the [MSHA]'s enforcement efforts.'" In April 2012, coal producer Alpha Natural Resources Inc. (ANR), the owner of the mine at the time, said it will permanently close its Upper Big Branch mine in West Virginia.Former Massey Energy CEO Don Blankenship was convicted in 2015 of a misdemeanor conspiring to willfully violate safety standards and was sentenced to one year in prison. He was found not guilty of charges of securities fraud and making false statements.