AN UNINTENTIONAL ROOF FALL OCCURRED IN THE 3-WAY INTERSECTION ON THE #1 ENTRY OF 60 + 50 6TH NORTH. THE FALL 18'WIDE, 60'LONG, 6'THICK. DID NOT IMPAIR VENTILATION OR IMPEDE TRAVEL. THE ROOF WA S SUPPORTED BY 6' DOUBLE LOCKING ROOF BOLTS. THE INTERSECTION WAS DEVELOPED MAY 2001.