A methane ignition occurred on 20 Rt. in No. 1 entry of new longwall face. Miner operator had cut approx 18' when mine roof fell in from face outby for the length of cut & approx 9' wide. The Sandstone rock that fell was 3' to 12"" thick. Mine operator was cutting up the rock to load out when the ignition occurred. The flame only lasted approx 15 sec & was extinguished w/water hose.