External effect of a vented explosion

Abstract : Various investigators noted that very significant explosions could result from the formation and ignition of a large combustible cloud following from a primary vented explosion. This phenomenon is sometimes referred to as " secondary explosion ". A systematic full scale experimental work (with vessel sizes ranging from 1 m3 to 100 m3 mixture of methane, propane and hydrogen with air) has been performed over a period of several years to understand better the underlying physics. Surprising results were 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. With help of high speed videos the nature and characteristics of the external cloud has been understood and the type of combustion studied. With this knowledge the nature of the interaction with the internal explosion has been clearly identified suggesting models to represent all the phenomenology.