Development of the hydrogen economy will require a better understanding of the potential for fires and explosions associated with the unintended release of hydrogen within a structure. The ability to predict the mixing and dispersion behavior of hydrogen, when accidentally released in a partially confined space (e.g. hydrogen leak from automobiles parked in a residential garage) is critical to the safe use of hydrogen products. Hydrogen release and dispersion in a garage can be simulated using computational fluid dynamic (CFD) tools. However, CFD software needs to be validated with experimental data before it can be used reliably for development of codes and standards appropriate for hydrogen fire safety. This paper assesses the capability of a CFD software package to simulate a set of experiments on the mixing and dispersion behavior of highly buoyant gases in a partially confined geometry. Simulation results accurately captured the overall trend measured in experiments conducted in a reduced scale enclosure with idealized leaks. The difference between experimentally measured peak concentrations and numerical simulation results, averaged over various heights was 2.3%. Sensitivity of the computed results on various model parameters was determined. Results indicate that the size of the leak has a small effect on the predicted concentrations, but the location of the leaks in the garage has a very significant effect on the computed results. This result has important implications on future modeling efforts as well as codes and standards related to hydrogen fire safety. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.