Hazardous gas releases in urban areas: assessment of consequences through CFD modelling.

Release of hazardous materials in urban areas is a major concern in industrial risk assessment. The presence of high population density in such areas multiplies the magnitude of the consequences. In urban areas, many buildings with complex geometries are involved leading to 3D flow fields that strongly influence gas dispersion. Representing such complex geometries simply but realistically in detailed simulation models can be cumbersome and often limit their utility. In this work, a methodology for the construction of 3D urban models and their importation into CFD models was developed through the access to spatial geodatabases, leading to a relatively fast and simple domain design technique. Moreover, since the magnitude of consequences depends on the absorbed dose which in turn depends on both concentration and exposure time, a simple methodology for dose evaluation was developed and implemented in a CFD code that enables the estimation of regions with a given death probability. The approach was developed and applied to a case study with different atmospheric stratification conditions. The results were then compared with those obtained using integral models. It was found that integral models can both overestimate and underestimate the magnitude of consequences related to hazardous material releases in urban areas.