At 4:45 p.m. on 9/14/11 the site lost power shutting down the fuel system. The system was restarted at 6:52 P.M. on 9/14/11. At 7:00 p.m. the coal in the mill self ignited causing an explosion. The mill was shut down and inspected. No damage to equipment or personnel occurred due to the safety dampers properly venting the combustion gases.