AN UNINTENTIONAL ROOF FALL OCCURRED ON THE 1ND MAIN NORTH BELT, AT A 4 WAY INTERSECTION.T HE FALL 18 FT LONG X 16 FT WIDE X 3 FT HIGH. THE FALL WAS DUE TO DEFERNATION OF THE IMMEDIATE ROOF. TH E AREA WAS MINED IN JAN. 1981 AND SUPPORTED W 8 FT EXPANSION BOLTS. THE FALL RESTRICTED PASSAGE OF MATERIAL ON THE BELT. ADDITIONAL SUPPORT SUCK AS CROSSBARS W/LEG WERE STEP IN THE EFFECTED A