THE COAL MILL WAS TURNED OFF AND THE NATURAL GAS PILOT LIGHT WAS TURNED ON. AFTER SEVERAL MINUTES THE EMPLOYEE'S WENT DOWN TO THE BASEMENT TO DO AN INSPECTION OF THE MILL. AFTER LOOSENING THE BOLTS ON 2 DOORS, THE TOP DOOR WAS TAKEN OFF FIRST AND THEN THE BOTTOM. AS THE BOTTOM DOOR WAS TAKEN OFF THE EXPLOSION OCCURRED.