AN UNINTENTIONAL ROOF OCCURRED 1 BLOCK OUTBY SURVEY STATION NO. 3144 IN NO. 8 ENTRY PRIMARY ESCAPEWAY. THE FALL WAS APPROX 40' X 16 1/2' X 3' HIGH. THE ROOF SUPPORT PRESENT HAD BEEN INSTALLED AFTER A PREVIOUS FALL. THE AREA WAS SUPPORTED WITH POSTS, XBARS & CRIBS. THE AREA WAS DANGERED OFF & POSTS WERE ADDED AT APPROACHES. THE ESCAPEWAY WAS REROUTED.