EMPLOYEE CLIMBED ONTO BACK OF FLATBED TRUCK, INSTALLED PUMP AND WAS TRANSFERRING OIL FROM 2 55-GALLON BARRELS TO 24K CRUSHER. WHEN HE WENT TO STEP DOWN OFF TRUCK, HIS FOOT SLIPPED AND HE FELL INTO TRAILER HITCH ON BACK OF TRUCK. THE HITCH CAUGHT HIM ON HIS RIGHT SIDE RIB AREA AND RIGHT WRIST.