AN UNINTENTIONAL FALL OF ROOF OCCURRED ON UNIT 4 IN #5 ENTRY AT 20+46'. THE FALL MESURED 60' LONG, 19' WIDE, 9' HIGH. NO ONE WAS INJURED, PASSAGE OF MEN OR VENTILATION WAS NOT AFFECTED. FALL W AS DUE TO ADVERSE ROOF CONDITIONS ABOVE 6' DOUBLE LOCK BOLT.