ROOF FALL ABOVE ANCHORAGE WHICH BLOCKED THE PASSAGE OIF MEN. THEFALL WAS AT #16 WALL, 3 WAY INTERSECTION, #1 RETIRM EMTRU/ALTERNATE ESCAPEWAY, 3-2 OFF 3NORTH. THE FALL WAS 20' WIDE BY 20' LONG AND 12' HIGH. THERE WERE NO INJURIES OR DAMAGE TO EQUIPMENT.