Hydrogen fuel cell railway vehicles are being developed as part of global efforts to decarbonize the railway sector. For their practical implementation, safety assessments are essential, particularly concerning hydrogen leakage in enclosed environments such as tunnels. The concentration of leaked hydrogen is strongly influenced by airflow conditions within the tunnel. This study employs numerical simulations to analyze hydrogen dispersion from a stationary two-car train situated inside a 400-meter-long single-track mountain tunnel on a conventional railway line in Japan. The leakage is assumed to originate from equipment mounted on the train roof. Simulations were conducted using the Fire Dynamics Simulator (FDS) developed by NIST. Results indicate that, in the absence of airflow, hydrogen concentration peaks directly above the leak source and rapidly decreases toward both tunnel portals, reaching the height of the overhead trolley wire. Conversely, even minimal airflow (less than 0.5 m/s) significantly reduces hydrogen concentration throughout the tunnel.
Fukuda et al. (Wed,) studied this question.