Tunnel-based numerical analysis and risk mitigation of high-pressure pure-hydrogen pipeline leakage

Research on hydrogen leakage primarily focuses on refuelling stations, while tunnel pipelines remain less studied. This study investigates 10 MPa hydrogen pipeline leakage in tunnels, analysing the effects of leak size, direction, and ventilation. Leak orifice size critically governs hydrogen accumulation. For diameters of 15 mm or smaller, the flammable volume ratio ( η ) increases gradually. For diameters of 20 mm or larger, η rises rapidly to a peak before a sharp decline, establishing 20 mm as the critical diameter. Leakage direction significantly influences distribution, with the -Z direction being most hazardous as it maintains η at 1.0 for 10 s at a 20 mm aperture. Ventilation effectively suppresses accumulation; a minimum wind speed of 2 m/s is required, and 4 m/s is recommended to strike a balance between safety and economy. These findings provide theoretical and data-driven support for the safety design and risk-based management of tunnel hydrogen pipelines.