Explosion risks in confined spaces hinder the widespread use of hydrogen fuel cell vehicles. This study investigates the consequences of hydrogen leakage and explosion accidents from fuel cell vehicles parked in underground garages. Results indicated that downward leaks generate a larger flammable gas cloud size, peak value of VQ8, and areas of danger 3, 1.2, and 2 more times than upward leaks. Meanwhile, upward leaks result in more extensive damage to steel structures and glass. Flammable gas cloud continuous accumulation occurs between beams owing to parking near a wall, whereas the flammable gas cloud maximum extent decreases by half upon parking adjacent to side walls. However, the radius of burns and minor injuries does not vary with parking position. Compared to a single-vehicle situation, multiple surrounding vehicles considerably expand the range of flammable gas clouds and burn hazard area with increases of 57.9% and 53%, respectively.