AT THE TIME OF THE INCIDENT, EE WAS INSTALLING A DESICCANT CARTRIDGE IN TO THE AIR DRYER OF A CAT OFF-HIGHWAY TRUCK. AS EE WAS TIGHTENING THE BOLT THAT HOLDS THE CARTRIDGE IN PLACE, USING AN I MPACT WRENCH, THE BOLT BROKE, ALLOWING THE CARTRIDGE TO FALL ON HIS HAND, CUTTING HIS THUMB. FOUR STITCHES WERE REQUIRED TO CLOSE THE LACERATION.