Influence of tunnel slope on hydrogen transport–dispersion characteristics and subsequent explosion consequences

To examine how tunnel slope affects hydrogen dispersion and explosion consequences after a leak, this study uses the CFD tool GASFLOW-MPI to simulate hydrogen leakage and dispersion in road tunnels with slopes of 0%, 9%, 18%, and 27%, and explosions in the 0% and 27% cases. Cloud morphology and hydrogen inventory above concentration thresholds are systematically compared. Results show that slope primarily affects the post-inertial dispersion stage: increasing slope enhances buoyancy-driven upslope transport while suppressing downslope dispersion. Ceiling-level hydrogen accumulation indicates potential flame acceleration and deflagration-to-detonation transition. Among the three representative ignition times, 4.2 s produces the highest peak overpressure, whereas 8.3 s gives the widest pressure-affected range; thus, 4.2 s is the most unfavorable in terms of peak overpressure. Deflagration heat release increases the inside–outside temperature difference and induces chimney-driven hot-cloud backflow, limiting mixing and dilution. At 4.2 s, hazards are comparable, with the horizontal tunnel marginally higher.