Toward consequence-based setback distances for outdoor bulk metal hydride-based solid-state hydrogen storage

This study presents a comparative safety assessment of outdoor bulk compressed gaseous hydrogen, liquid hydrogen, and metal hydride-based solid-state hydrogen storage systems, with a focus on setback distance determination based on simulated results of unignited plume dispersion, heat hazards, and unconfined overpressure hazards. Simulations were conducted under a unified modelling framework under conservative outdoor conditions. Hydrogen releases were assumed to occur in the horizontal direction at ground level to determine the maximum horizontal extent of hazard zones and, consequently, conservative setback distances. Fractional leak sizes and harm criteria were selected in accordance with relevant standards. The results reveal clear differences in hazard behaviour among the three storage systems, with compressed gaseous hydrogen storage systems generally produce the largest setback distances, across all investigated pipe internal diameters and exposure groups, while metal hydride-based solid state hydrogen storage systems consistently exhibited the smallest hazard footprints. For highest-pressure cases with the largest pipe internal diameters (2 in.) investigated, setback distances range from 27.2 to 37.2 m for compressed gaseous hydrogen across the three exposure groups, whereas those for metal hydride-based solid-state hydrogen are reduced to 4.9–6.3 m. In addition to its reduced hazard distances, metal hydride-based solid-state hydrogen storage system also provides the highest volumetric hydrogen storage density, supporting more compact installations and improved land-use efficiency. These findings highlight the inherent safety and spatial advantages of metal hydride-based solid-state hydrogen storage systems and offer the first quantitative evidence base to inform the future development of safety criteria, preliminary design guidelines and standardisation efforts for metal hydride-based solid-state hydrogen technologies. Schematic comparison of setback distances for compressed, liquid, and metal hydride hydrogen storage systems. • Risk-informed framework for metal hydride hydrogen storage setback distances. • Quantitative simulation evidence for metal hydride hydrogen storage safety design. • Linear leak size to setback distance relationships for scalable estimation. • Basis for future codes and standards for metal hydride hydrogen storage systems. • Comparative simulation of setback distances across three storage systems.