AT THE TIME OF THE INCIDENT, EE WAS INSTALLING A WASTE GATE UPDATE ON THE AIR TANK OF A CAT 793 OFF-HIGHWAY TRUCK. TO RECONNECT THE AIR LINES ONT HE BOTTOM OF THE AIR TANK, EE HAD TO LEAN OVER THE FIRE SUPRESSION SYSTEM BOTTLES AND REACH DOWN BETWEEN THE BOTTLES AND THE AIR TANK. AS HE DID THIS HIS FEET SLIPPED OUT FROM UNDER HIM, CAUSING HIM TO FALL AND TWIST BACK.