Hydrogen and methane as alternative energy sources introduce new safety challenges, particularly when they are stored in enclosed spaces. In the event of high-pressure gas leakage through small openings, a flammable mixture may form and gas may accumulate beneath the ceiling. The leakage of hydrogen and methane from a full industrial gas cylinder into an 8 x 6 x 3 m enclosure was modelled using the Fire Dynamics Simulator. The highest concentrations of combustible gases were observed near the ceiling, where, under quasi-steady conditions, the average concentrations were approximately 14% methane, 10% hydrogen and 16% oxygen. The flammability zone of the mixture was determined using Le Chatelier’s rule and extended approximately from 1.2 to 2.4 m above the floor. The model was then supplemented with an ignition source to analyse the combustion dynamics. The maximum temperature in the enclosure reached 1911 °C, while the peak heat release rate was 13.5 MW, occurring 7.8 s after ignition. During combustion, approximately 193 MJ of energy was released, corresponding to about 45% of the theoretically available energy of the fuel mixture.
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