Experiments on buoyant gas dispersion in an enclosure have been conducted in a facility of the typical size of a private garage. Helium is used as a model gas for hydrogen. For release flow rate of the order of 0.1 Nl/min to 10 Nl/min, the dispersion is studied in a tightly sealed configuration of the enclosure and for two vertical positions of a vent, near the bottom and near the top. Results are compared to existing simple analytical models. A good accordance is found in the tightly sealed case. With one vent, some significant differences with models are found for the highest flow rates due to a vertical stratification. However a good accordance is found in the limit of very low flow rates even for the simplest model based on a ventilation flow rate independent of the interior mixture density. The main properties of the equivalent flammable atmosphere formed with the vent are presented. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.