Hydrogen is a promising alternative fuel which is expected to gain a significant portion of the energy market in the near future. However, it is a flammable gas with significant safety concerns as it can easily cause deflagrations or even detonations. The aim of this work is twofold: firstly, to derive a new CFD model for vented deflagration simulations improving an existing one and secondly, to better understand the physics of the phenomenon. A recent experiment conducted in Karlsruhe Institute of Technology is used for that purpose. The new model improves substantially the predictions representing successfully the experiment. The analysis indicates that turbulence generated outside the vent is responsible for the violence of the external explosion which leads to the sudden pressure increase. Rayleigh-Taylor instability on the other hand does not seem to contribute to burning velocity increase. From the analysis that is made combustion models are formulated highlighting the important components for a successful CFD deflagration model. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.