AN UNINTENTIONAL ROOF FALL ON NORTH MAIN ENTRY #3 AT SPAD 6569 WAS 90 FT LONG 20 FT WIDE AND 4 FT THICK. THE FALL WAS ABOVE ANCHOR. 4 FT RESIN BELT WAS USED ALONG WITH TEMBERST CRIBS. PASSAGE WAS BLOCKED. VENTILATION WAS NOT AFFECTED, NO EQUIPMENT WAS DAMAGED AND NO INJURY.