ACE (Airborne Concentration Estimate) is a model originally developed by WS Atkins on behalf of HSE for computing source terms arising from instantaneous flashing releases. The model has since been reviewed and enhanced through a series of extensive tests that have been performed by HSL. Inputs to ACE are the substance, its mass and storage conditions and ambient weather conditions. The model then computes the formation of a vapour cloud assuming total loss of containment. This is done in two distinct stages; an explosion phase, which models the initial flashing process and a turbulent growth stage, describing further radial expansion and air entrainment. The resulting cloud properties can be used as the input to an atmospheric dispersion model. This report describes an updated validation of ACE in which overall cloud radius predictions have been compared with those obtained from experiment. In addition, an attempt has been made to further the validation by comparing cloud expansion velocities. This was not previously carried out for ACE and was considered an area where the validation could be enhanced.
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