A LOAD OF ROOF STRAPS HAD BEEN LOWERED TO THE BOTTOM. THE HITCH HAD BEEN LEFT OUT OFF THE FRONT OF THE SUPPLY TRAILER. THE ROOF STRAPS WERE HANGING OVER THE FRONT OF THE TRAILER BLOCKING ACCES S TO THE HITCH CONNECTION POINT. EE USED THE HOIST ON THE BOTTOM TO RAISE ONE END OF THE STRAPS OUT OF HIS WAY. HE USED 2 CHAINS TO LIFT THE STRAPS AND 1 OF THEM SLIPPED STRIKING HIM ON ARM.