EMPLOYEE WAS TRYING TO FREE A HOIST CHAIN WHICH HAD BECOME CAUGHT IN THE SECTION OF FLOOR GRATING THE EMPLOYEE WAS STANDING ON. THE GRATIN GTWISTED UNDER THE FORCE APPLIED ON IT, ALLOWING TH E EMPLOYEE TO FALL. THE EMPLOYEE HIT HIS BACK AGAINST THE CONCRETE SLAB THAT JOINED THE GRATING RESULTING IN A SEVERE BRUISE TO THE SPINAL AREA.