While traveling to start a belt that was down, the section foreman noticed a fall had occured. This was in the 1st southwest mains belt entry, two crosscuts inby spad 1836. Approx 20' wide x 30' long x 9"" high. The area was cribbed, timbered and bolted. All accesses to the fall were dangered off. Vent tubing was humg to divert gas to return.