A computational fluid dynamics (CFD) approach using the standard k - epsilon turbulence model was applied to simulate hydrogen and methane dispersion around a cubical building. Model results were compared against towing-tank data and other numerical results. The relative impact between hydrogen and methane releases on the building and its surroundings under several stable atmospheric stratifications was assessed. The computed dispersion patterns show a greater risk potential of hydrogen in comparison to methane when released in the vicinity of a building. However, since hydrogen rapidly rises, the impact of a release on the surrounding buildings promptly diminishes. The results also depict complex interactions of hydrogen dispersion patterns due to strong buoyant forces. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.