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RR369 - Research to improve guidance on separation distance for the multi-energy method (RIGOS)

This report describes the RIGOS-research program. The primary objective of this program was to develop practical guidance with regard to the Critical Separation Distance. The Critical Separation Distance is a basic element in the application of the TNO Multi-Energy method for vapour cloud explosion blast modelling. To this end, a series of gas explosion experiments have been performed in a donor acceptor configuration. The blast was recorded at several positions around while the separation distance between donor and acceptor was gradually diminished. When the blast was observed to consist of just one single instead of two separate waves, the separation distance was assumed critical. The experimental program resulted in a limited number of concrete indications with respect to the Critical Separation Distance, in particular in the low explosion overpressure range. On the basis of this limited information concrete guidance was drawn up based on safety and conservatism. This guidance was extrapolated to the high explosion overpressure range on the basis of common sense.

Apart from this primary objective, the RIGOS program led to a substantial amount of additional and interesting information. The data show, for instance, that for separation distances somewhat larger than critical, the donor explosion may largely suppress the acceptor explosion. The gas dynamics of the donor’s negative phase could explain this surprising observation. The experimental data also gave the opportunity to validate current simple blast modelling methodologies on the acceptor gas explosion data. Because of the directional flame propagation mode in the acceptor, the acceptor gas explosions differ substantially from the spherically developing gas explosions, the simple blast modelling methodologies were derived from. The conclusion is that the current simple blast modelling methodologies tend to overestimate the blast effects from the acceptor explosions by more than an order in magnitude, in particular in the low explosion overpressure range.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.

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Updated 2012-03-26