EMPLOYEE WAS UNDER THE HEAT EXCHANGE FOR KILN #4 ATTEMPTING TO REMOVE THE BELLOWS FROM THE HEAT EXCHANGE TUBES USING AN AIR HAMMER. ONE 30' TUBE LOOSENED IN THE TUBE SEAT AND FELL STRIKING HIS LEFT THUMB WHICH WAS HOLDING THE AIR HAMMER. HE RECEIVED SEVERAL STITCHES AT THE LOCAL HOSPITAL AND WAS GIVEN MEDICATION.