EE'S WERE ASSIGNED TO REMOVE THE BELT TENSION BY LIFTING THE COUNTERBALANCE OF CONVEYOR BELT. THEY STARTED SETTING UP THE BELT & HOOKING THE SLINGS TO THE CRANE & THE COUNTERBALANCE. THE CRANE STARTED LIFTING W/O ANY DIFFICULTIES. THEN THE BOOM TURNTABLE STARTED RIPPING APART, CAUSING THE BOOM TO FALL OVER ONTO THE CONVEYOR BELT. EE WAS PINNED BETWEEN THE HANDRAIL & BELT. FX BACK.