AN UNPLANNED ROOF FALL OCCURRED AT 1300 ON 7-28-00. TYPE OF AIRWAY WAS NEUTRAL. VENTILATION WAS NOT AFFECTED. THERE WERE NO PERSONAL INJURIES AND NO EQUIPMENT WAS INVOLVED. SIZE OF FALL MEASUR ED 50' X 20' X 8-9'. ALL ENTRANCES TO THE FALL HAVE BEEN BREAKERED OFF.