The comparison between experimental data and simulation results of hydrogen explosions in a vented vessel is described in the paper The validation exercise was performed in the frame of the European Commission co funded Network of Excellence HySafe (Hydrogen Safety as an Energy Carrier) that has the objective to facilitate the safe introduction of hydrogen technologies The mitigation effect of vents on the strength of hydrogen explosions is a relevant issue in hydrogen safety Experiments on stoichiometric hydrogen deflagrations in a 0 95 m(3) vessel with vents of different size (0 2 m(2) and 0 3 m(2)) have been selected in the available scientific literature in order to assess the accuracy of computational tools and models in reproducing experimental data in vented explosions Five organizations with experience in numerical modelling of gas explosions have participated to the code benchmarking activities with four CFD codes (COM3D, REACFLOW, bob and FLUENT) and one code based on a mathematical two zone model (VEX) The numerical features of the different codes and the simulations results are described and compared with the experimental measurements The agreement between simulations and experiments can be considered satisfactory for the maximum overpressure while correctly capturing some relevant parameters related to the dynamics of the phenomena such as the pressure rise rate and its maximum has been shown to be still an open issue (C) 2010 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reserved