WHILE WALKING #3 BELT, EE HEARD ROOF BOLT POP. HE TURNED TO LOOK BACK AND SLIPPED OFF OF BRIDGE MATERIAL. LOST BALANCE AND REACHED FOR PIPE CHAIN TO CATCH HIS BALANCE. FELT PAIN IN LEFT SHOULDER AND LOWER BACK. AREA WAS WET AND MUDDY. EE BEGAN MISSING WORK ON 6-4-04. DIAGNOSED AS A ROTATOR CUFF TEAR ON 6-4-04.