(47cq) Building Siting Evaluation: A New Software Tool for the Determination of Blast Loads from Potential Vapour Cloud Explosions (VCEs)

A central element of building siting evaluation—especially where vapour cloud explosion (VCE) hazards are credible—is the calculation of the blast parameters/loads to buildings of interest. This determination is typically approached in two ways. Using simplified models that utilize blast curves (notably the TNO Multi-Energy and Baker Strehlow Tang models), or advanced methodologies using computational fluid dynamics (CFD) technology. Simplified models are more widely used as they offer a good level of characterization potential and are more pragmatic to use. The latter (i.e. CFD) can be resource and time intensive and is typically reserved for instances where the simplified models are limited (e.g. in the determination of near field blast loads).

A rigorous application of the simplified approaches would typically involve dispersion modelling (under specific conditions e.g. weather and wind speed) for the identified loss of containment scenario (or scenarios) to evaluate the size of the resulting flammable cloud and the potential for (and degree of) interaction with any identified regions of congestion and/or confinement. However, such a task is not trivial and to reduce the calculation burden this analytical step is sometimes bypassed and a simplifying assumption that the entire region is full of flammable gas is made.  Whilst such an assumption ensures a conservative, cautious approach to the analysis, it does not reflect reality and can result in outcomes that are excessive to requirements – the upshot of which can be sub-optimal resource allocation. Consequently, there is a need for an approach that allows for a more realistic analysis of VCE potential.

This paper describes an advanced implementation of the two most widely used vapour cloud explosion models mentioned above, namely the TNO Multi Energy (ME) Method and the Baker-Strehlow-Tang (BST) model, into Phast, the well-known general purpose consequence analysis software package developed by DNV GL Software. A key aspect of this new addition is the capability to examine the interaction of a dispersing dynamic flammable cloud profile with congested/confined regions in all three dimensions (length, width and height) and in multiple directions.  This is in direct response to the aforementioned challenge and the intention is to provide a robust platform by which a more detailed analysis of the VCE hazards can be evaluated without recourse to simplification.

The implementation of both models is extensive and includes all the key parameters that have a bearing on the magnitude of a vapour cloud explosion. A case study of the tool as applied to a hypothetical occupied building siting challenge is presented and the value of using the tool discussed.