Numerical simulations of the release of liquid hydrogen from a freight train and explosion in a long railway tunnel: Consequences for passenger train safety

Railway transport is emerging as a flexible solution for the distribution of liquid hydrogen (LH2). However, LH2 might cause safety concerns in railway tunnels, especially when passenger and freight trains are allowed to transit simultaneously in the same tube. Since the issue is relevant, 3D computational fluid dynamics models were developed to simulate the hydrogen dispersion and explosion in a long single bore, double-track railway tunnel. The scenario considers a freight train transporting LH2 experiencing a loss of containment and to stop in a 5 km long tunnel, while a passenger train queues and stops upstream on the same rail track at different distances from the freight one. The natural and mechanical ventilation conditions were investigated. A probabilistic assessment based on probit models was then performed to estimate the consequences for the passengers. The results indicate that a fatality probability less than 1 % might be achieved when the passenger train stopped at a safety distance from the freight train ≥ 2000 m in the case of the tunnel naturally ventilated, while a shorter distance (i.e., ≥ 1700 m) might be sufficient when the mechanical ventilation, which pushed the airflow in the same travel direction of the two trains, was considered. In the case in which the two trains moved on opposite tracks, the safety distances between the front of the passenger train and the point of LH2 release were found to be ≥ 1600 m or ≥ 2100 m when the tunnel tube was naturally or mechanically ventilated, respectively. In this last case of the mechanically ventilated tunnel, however, the possibility of reversing the fan direction is also recommended as a mitigation strategy.