EE WAS WORKING ON D9L #1222 DOZER. HE WAS GOING TO PUT A DIPSTICK TUBE UNDER THE FLOOR OF THE DOZER. HE TOOK THE FLOOR BOARD OUT OF THE CAB, CLOSED THE DOOR, GOT DOWN OFF THE DOZER TO GET WRENCH AND NEW PART, GOT BACK UP ON THE DOZER. HE OPENED THE DOOR AND STEPPED IN FALLING THROUGH THE HOLE IN THE FLOOR. BRUISED LEFT LUNG AND HAIR LINE FRACTURE OF RIB.