Numerical modeling towards the safety assessment of multiple hydrogen fires in confined areas

Hydrogen fuel cell vehicles (FCVs) have been considered an option for the future zero-emission transport sector. However, there are some safety concerns about FCVs in restricted environments. Risk analysis of possible fire scenarios is an efficient approach to identifying, evaluating, and mitigating the risk from hydrogen fire accidents. Computational fluid dynamics (CFD) simulations were conducted for a 102 m long tunnel to analyse the influence of multiple hydrogen fires having different heat release rates (HRR). The developed model was first validated against published data. A detailed computational analysis of multiple hydrogen fires was then conducted to understand the influence of HRR, leakage area, ventilation velocity, the presence of sloping, and the sealing ratio of the tunnel. In the absence of inlet velocity, the high thermal zones are closer to the tunnel ceiling at the fire’s location. With increasing the inlet air velocity, the overall ceiling temperature reduces, although the high-temperature zones are pushed further downstream. Increasing the leakage area enhances the HRR, and hence the impact of the heat feedback mechanism becomes more significant since larger HRRs account for higher temperatures, strong flame interactions, and low oxygen concentrations. The results show that the higher sealing ratio of the tunnel leads to an increase in the peak ceiling temperatures. It is also observed that the presence of sloping increases the severity of fires as high-temperature zones and oxygen deficiency is observed at the higher locations of the tunnel from ground level.