CUSTOMER ON MINE SITE TO GET A LOAD OF GRAVEL BUT BEFORE DOING SO HE RAISED THE BED OF HIS TRUCK TO CLEAR IT OF DEBRIS. THE BED WAS UP APPROX 18"" TO 24"" WHEN A PROBLEM WITH THE HOISTING MECHAN ISM CAUSED THE INJURED TO REACH IN BETWEEN THE RAISED TRUCK BODY AND THE TRUCK FRAM (THE TRUCK BODY WAS NOT BLOCKED AGAINST MOVEMENT) WHEN THE TRUCK BED FELL ON HIS ARM.