EE'S WERE ASSIGNED TO REMOVE TENSION BY LIFTING THE COUNTERBALANCE OF CONVEYOR BELT. THEY STARTED SETTING UP THE BELT & HOOKING THE SLINGS TO THE CRANE & COUNTERBALANCE, THE CRANE STARTED LIFT ING W/O ANY DIFFICULTY. IN A MATTER OF SECONDS THE BOOM TURNTABLE STARTED RIPPING APART, CAUSING THE BOOM TO FALL OVER ONTO CONVEYOR BELT. EE HIT BY HANDRAILS & PINNED BETWEEN BELT & RAILS.