The mine owner and operator have been cited repeatedly for potentially dangerous conditions, including high levels of combustible methane gas and Massey paid out $US4.2 million ($A4.53 million) in criminal and civil fines last year. Coal mining is a key industry in West Virginia, with 150 million tonnes produced each year, second only in coal production to the state of Wyoming. In the last major mine explosion, in January 2006, 12 people died in a coal mine owned by the International Coal Group in Sago, West Virginia, after they were trapped by an explosion 80 metres underground.