Hazard assessment of complex hydrides as hydrogen storage materials

Hydrogen storage materials containing NaAlH4, LiNH2, Mg(NH2)2, LiH and LiBH4 were subjected to standardized safety tests in order to assess the potential hazards caused by the environmental exposure of these materials. All the materials were judged ‘flammable’, ‘pyrophoric’ and ‘water-reactive’, resulted in being classified as the United Nations Packing Group I, the most stringent category of container regulations in transporting these materials. A small spark energy (1.4 mJ) can trigger an intense dust cloud explosion of the Mg(NH2)2 + LiH system of which the minimum explosive concentration was determined to be 90 mg dm−3. Although this value is lower than those of the hydrogen storage alloys, the minimum explosive concentration of complex hydrides can be comparable to the alloys if expressed in terms of the amount of stored hydrogen in the material. Also examined was the eruption test, a non-standard test, in which the sample powder was pushed out of a container into the atmosphere by pressurized H2. Despite the pyrophoricity, we observed only one explosion of the Ti-doped NaAlH4 in dozens of trials using all the materials. A comparison with other materials points to the inevitability of more cautious measures than metal hydrides when handling these complex hydrides.