An unintentional roof fall occurred on the old 1A return @ station 31+80 between entries 9 and 10. The fall did affect the ventilation on the #4 unit which was idled until all work was completed and ventilation re-established. The fall did not affect passage of men or cause personal injury. The fall had been bolted with 6 ft. fully grouted roof bolts and 12 foot cable bolts.