COAL MILL FEED CHUTES WERE PLUGGING UP DUE TO WET COAL. REMOVABLE GUARD RAIL WAS TAKEN DOWN AND EMPLOYEE WAS ATTEMPTING TO UNPLUG CHUTE. HE HAD LEFT THE AIR BLASTER ON AND IT BLASTED, CAUSING HIM TO FALL OFF OF MILL. HE HAS FRACTURED RIBS &CONTUSION TO LUNG.