Investigation of the mitigation of gas cloud explosions by water sprays

Experiments have been carried out to investigate the ability of water sprays to limit flame speeds and overpressures produced in gas cloud explosions. In experiments involving flame propagation through repeated arrays of pipework obstacles, successful results were obtained using water sprays produced by two different types of nozzle currently used in deluge systems on offshore platforms. These water sprays restricted flame speeds in both nominally stoichiometric natural gas-air and propane-air mixtures. Overpressures were reduced by about an order of magnitude. Experiments using a full water deluge in a geometry representative of an offshore module, have confirmed this beneficial effect, with maximum overpressures of a few hundred millibar being generated. A theoretical study of the effect of water sprays as a means of mitigating explosions suggests that sprays producing small droplets and generating low turbulence levels may be the most effective. This is consistent with results obtained from further experiments carried out with a range of different nozzles.