Abstract: A detonation flame arrester (10) in a gas pipeline (11), comprises a detonation arresting element (12) and a separate deflagration arresting element (23), the detonation arresting element comprising parallel channels having a typical transverse dimension of the same order of magnitude as the detonation cell width of the gas in the pipeline. The walls of the channels are of non-porous material so that the channels are not connected. The elements (12, 23) may be spaced apart or in contact. The elements may be located in an expanded section (17) of the pipeline, or in the pipeline itself.