When designing high-pressure gas pipelines, it must be ensured that a running fracture is arrested within the shortest possible length. The semi-empirical Battelle Two-Curve Model (BTCM) proposed in the early 1970s is still widely used in the industry to estimate the required toughness of the pipe wall material. The BTCM method requires accurate prediction of the gas decompression wave speed. In this paper, a Computational Fluid Dynamics (CFD) model is proposed to predict the decompression wave speed of high-pressure Hydrogen-Natural Gas (H2NG) mixtures in pipelines. The CFD model is validated against experimental data. Three Equations of State (EOS): the Peng-Robinson (PR) EOS, the AGA8 EOS and the GERG-2008 EOS, are incorporated into the CFD code to estimate the physical properties of the mixtures. The ability of the three EOS to predict the decompression wave speed is evaluated by comparing the predicted results against experimental data. Also, the influence of H 2 fraction in the H2NG mixture on the decompression wave speed is investigated.