Computational Fluid Dynamics (CFD) modelling of atmospheric dispersion for land-use planning around major hazards sites in Great Britain

The Health and Safety Executive (HSE) is the statutory authority in Great Britain responsible for providing public safety advice to planning authorities on the risks associated with proposed new developments (e.g. housing, schools, hospitals) near major hazards sites and major accident hazard pipelines. For those sites where there is the potential for an atmospheric release of toxic or flammable substances, HSE currently uses the integral dispersion model DRIFT to quantify the potential hazard. However, HSE has recently faced pressure from developers to accept results from Computational Fluid Dynamics (CFD) models. A benefit of CFD models is principally that they can take into account the presence of terrain and complex obstructions, whereas integral models such as DRIFT assume flat terrain and account for obstacles as a uniform roughness. However, there are a number of unresolved problems with CFD models that need to be addressed in order for HSE to have confidence in their results for use in Land-Use Planning (LUP) assessments. The purpose of this paper is to discuss the challenges associated with using CFD in this specific regulatory context. The aim is to inform the decision on whether or not to accept the use of CFD modelling and to help prioritise future research activities.