A MAINTENANCE MECHANIC WAS ATTEMPTING TO REMOVE A PIPE FROM THE BALL MILL DISCHARGE. WHEN THE PIPE CAME LOOSE IT STRUCK THE SLEDGEHAMMER HE WAS HOLDING IN FRONT OF HIS FACE, KNOCKING THE HEAD OF THE HAMMER AGAINST HIS SAFETY GLASSES. IT WAS DTERMINED THAT THE IMPACT OF THE HAMMER AGAINST HIS GLASSES CAUSED THE CHEEK LACERATION THAT REQUIRED FOUR STITCHES TO CLOSE.