REPAIR WORK WAS BEING PERFORMED ON A LOADER TO THE CUTTING EDGE. EE WAS STANDING AT THE REAR OF HIS MECHANIC'S TRUCK ~30' AWAY FROM WHERE THE WORK WAS BEING PERFORMED. THE WELDER PERFORMING TH E WORK TO THE CUTTING EDGE WAS STRIKING IT WITH A SLEDGEHAMMER WHEN APPARENTLY A PIECE OF METAL BROKE LOOSE AND STRUCK EE IN THE LEFT TEMPLE AREA OF THE HEAD. THE PIECE OF METAL BECAME IMBEDD