In this paper, the transient hydrogen gas leakage in a closed cylinder chamber is being numerically simulated. The results of the simulation were compared against an experimental and two other numerical simulations results. To identify the behavior of hydrogen gas and the risks of its leakage and diffusion of hydrogen gas, the model parameters are studied. Parameters investigated are the height of leakage hole location and leakage direction in the chamber. In each case, the hydrogen volume fraction graphs and created hazard region height at various time and also hazard region completely disappearing time, are investigated and high-risk states are marked. (c) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.