The influence of water mist on explosion of H₂-air mixtures is studied experimentally in a closed channel with rectangular cross section. The investigated range of H₂ concentrations covers slow flames, accelerating flames, transition to detonation and detonations. Water loading ratios particularly relevant for severe accident scenarios in nuclear power plants are examined. A system for water mist generation and injection was designed such that the experimental conditions are well defined. The water loading ratio is determined by extinction measurement in each experiment. Laser diffraction measurements provide the droplet size distribution. Water mist injection results in lower overpressure and retarded transition to detonation compared to dry H₂-air mixtures. The effect of a 0.11–0.12 kg/m³ water loading ratio is comparable to a decrease in H₂ concentration by 0.6%vol in the deflagration regime and by 1–2%vol in the detonation regime, while transition to detonation is retarded more significantly.