Abstract: Through an experimental study on the flame and pressure structures of the gas explosion in a horizontal pipe, the failure cause of the suppression and isolation apparatus for gas explosion is analyzed. The results show that the explosion flame is very long with cohesive force, and propagates along the bottom of the pipe. The main cause of failure for this apparatus is that the delay-time of the apparatus for operation is not consistent with the required arrival time of the flame to the apparatus. It makes the released inhibitor could not cover the whole flame area, so that the flame, pushed by the high explosion pressure behind the flame, continuously propagates forward.