(111a) The Dynamics of Vented Gas Explosions

The results of a large test series on vented gas explosions are herein reported (with vessel sizes ranging from 1 m3 to 100 m3 mixture of methane, propane and hydrogen with air). The pressure has not only been measured internally but also externally ; the flame propagation has also been recorded with a speed camera. It is shown that a very significant explosion could result from the formation and ignition of the combustible cloud outside the vent and that, in a number of circumstances, this ?external? explosion would overcome the internal one. Surprising results were also obtained showing for instance that near the vent the maximum overpressure may be lower than further downstream not because the external explosion is developing far downstream but because of the local influence of rarefaction waves produced at the vent. But the mode of combustion of the external cloud is still outstanding and cannot be described by the traditional outward expanding flame kernel.