EMPLOYEE WAS HELPING UNLOAD COKE RAILCARS. WHEN THE CAR WAS EMPTY HE WAS TO UNHOOK THE CHAIN CONNECTING THE CAR SHAKER TO RAILCAR. HE DID NOT DO SO AND WHEN THE HOIST WAS LIFTED AND CAR STARTE D TO MOVE THE TENSION ON THE CHAIN CAUSED IT TO SNAP AND SWING IN HIS DIRECTION AND COME IN CONTACT WITH HIS LEFT ARM, FACE, AND RIBS.