Accidental release and dispersion of toxic gases were always major hazards for public health and safety that process industries had to deal with. Real terrain dispersion simulation for risk analysis purposes poses specific difficulties related to complex turbulence phenomena development, especially when obstructions are found into the flow region. In this paper, several turbulence models are tested and compared against experimental data of dense vapor dispersion, in order to decide for their suitability for simulating such flows. Computations were carried out using the computational fluid dynamics (CFD) code CFX 5.6, while experimental data were obtained from Thorney Island large scale field trials. Computational results showed good agreement with experimental measurements indicating that CFDs provide a reliable means of estimating gas dispersion in real terrains.