The use of stationary H(2) and fuel cell systems is expected to increase rapidly in the future. In order to facilitate the safe introduction of this new technology, the HyPer project, funded by the EC, developed a public harmonized Installation Permitting Guidance (IPG) document for the installation of small stationary H(2) and fuel cell systems for use in various environments. The present contribution focuses on the safety assessment of a facility, inside which a small H(2) fuel cell system (4.8 kW(e)) is installed and operated. Dispersion experiments were designed and performed by partner UNIPI. The scenarios considered cover releases occurring inside the fuel cell at the valve of the inlet gas pipeline just before the pressure regulator, which controls the H(2) flow to the fuel cell system. H(2) was expected to leak out of the fuel cell into the facility and then outdoors through the ventilation system. The initial leakage diameter was chosen based on the Italian technical guidelines for the enforcement of the ATEX European directive. Several natural ventilation configurations were examined. The performed tests were simulated by NCSRD using the ADREA-HF code. The numerical analysis took into account the full interior of the fuel cell, in order to investigate for any potential accumulation effects. Comparisons between predicted and experimental H(2) concentrations at 4 sensor locations inside the facility are reported. Finally, an overall assessment of the ventilation efficiency was made based on the simulations and experiments. (c) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.