Hydrogen is an enabler for de-carbonising the energy system in Europe by 2050. In the UK, several projects are investigating the feasibility of gradually blending hydrogen into the natural gas pipelines with the aim to reach 100% hydrogen in the gas network. However, the safe use of hydrogen as a fuel presents different challenges than conventional hydrocarbon-based fuels Advanced consequence models are powerful tools that can be used to support the design process and estimate the consequences of potential accidents. This paper analyses the predictive capabilities of two combustion models for explosion for hydrogen, methane and hydrogen-methane blends. The analysis involves the default combustion model in the commercial version (FLACS-CFD v21.2), and a new combustion model implemented in an in-house development version where the model for premixed turbulent combustion incorporates Markstein number effects (FLACS-CFD v21.2 IH). Experiments performed by Shell in unconfined pipe-racks, some of which were part of the EU funded project NaturalHy, are considered. The simulation results from both versions of FLACS-CFD are within a factor of 2 of the overpressures observed in the experiments. However, FLACS-CFD v21.2 IH appears to give an improved representation of the overpressure trend with variations in the hydrogen equivalence ratio observed in the experiments.