The study of the consequences of heavy gases releases is of paramount importance in the safety analysis because of the large damage areas involved. The Computational Fluid Dynamics (CFD) models, unlike the integral ones that are simpler and faster, allow for a complete description of complex geometries, such as those involved in industrial plants or urban areas. In this work, the effect of typical large obstacles present in a real plant has been studied. Moreover, to verify the effectiveness of mitigation barriers on the dispersion of clouds produced by massive release of heavy gases, several types of walls have been investigated by analyzing the induced changes in the hazardous area.