A NON-INJURY ROOF FALL WAS DISCOVERED AT APPROX 3:00 PM AT THE 32ND CROSS-CUT IN THE RETURN ENTRY ALONG THE NO.1 BELT LINE MAINS. THE ROOF FALL IMPAIRED THE VENTILATION FOR THE RETURN IN THIS AREA. THE FALL MEASURED APPROX 19 FT WIDE, 0 TO 8 FT THICK, AND 30 FT LONG.