In this paper, CFD techniques were applied to the simulations of hydrogen release from a 400-bar tank to ambient through a Pressure Relieve Device (PRD) 6 mm ( ) opening. The numerical simulations using the TOPAZ software developed by Sandia National Laboratory addressed the changes of pressure, density and flow rate variations at the leak orifice during release while the PHOENICS software package predicted extents of various hydrogen concentration envelopes as well as the velocities of gas mixture for the dispersion in the domain. The Abel-Noble equation of state (AN-EOS) was incorporated into the CFD model, implemented through the TOPAZ and PHOENICS software, to accurately predict the real gas properties for hydrogen release and dispersion under high pressures. The numerical results were compared with those obtained from using the ideal gas law and it was found that the ideal gas law overestimates the hydrogen mass release rates by up to 35%2during the first 25 seconds of release. Based on the findings, the authors recommend that a real gas equation of state be used for CFD predictions of high-pressure PRD releases.