EE WAS SCALING FLOOR PAD AREA AROUND #4-9 FLASH TANK USING A RIVOT GUN. WAS PUTTING PRESSURE AGAINST GUN WHEN SCALE DISLODGED FROM PAD & CAUSED GUN TO JUMP FORWARD UNEXPECTEDLY. HANDLE OF GUN STRUCK SOME PIPING JUST FORWARD OF WHERE EE WAS WORKING PINCHING HIS RIGHT THUMB BETWEEN GUN & PIPE. EE IS NOT LOSING TIME OR ON WORK RESTRICTIONS.