This study employs numerical simulation and three-dimensional concentration-field visualization to systematically elucidate the diffusion behavior and risk evolution of hydrogen leakage from a fuel cell vessel under varying wind conditions. The results indicate that, in no wind condition, hydrogen diffusion proceeds through three stages—jet impingement, turbulence-driven mixing, and buoyancy-induced stratification—and that obstacles within the confined space disrupt symmetric spreading. A flammable region forms within 0.5 s, with a peak flammable volume of 15.1 m3, which then decays rapidly as the leak rate diminishes. Under crosswind conditions, shear from the ambient wind markedly alters both the diffusion direction and rate. Wind from the negative X-axis (X-) prolongs the retention of flammable volume, whereas wind from the positive X-axis (X+) accelerates volume decay due to enhanced turbulence. In tailwind (Y+) scenarios, strong convective transport drives far-field diffusion, while near-field accumulation remains pronounced, delaying the flammable-volume peak until 7.5 s. Hazardous-volume analysis further demonstrates that the wind field governs the spatiotemporal distribution of risk via momentum coupling and turbulence modulation: in the no wind condition, the hazardous volume peaks at 83.6 m3, whereas under X+ wind, it is reduced to 33.0 m3. These findings reveal that the interaction among hull geometry, wind direction, and leak dynamics significantly influences the risk of hydrogen explosions, providing a scientific basis for optimized sensor placement and emergency-response planning.