The critical mass for the unconfined vapour cloud explosion of compressed and liquid hydrogen

The (unconfined) vapour cloud explosion (VCE) is a dramatic phenomenon that generates severe pressure wave with high potential to damage assets and produce injuries in the far field. This definition applies also hydrogen. Nevertheless, no clear tools methodology have been so developed tested for this highly reactive gas, even advanced numerical simulations lack validation suffer from large uncertainties. In view, comprehension of physic which subtends specific case hydrogen still central issue. paper revises some most adopted theories on VCE based classical acoustic theory models propagation provides consequence-based, threshold (minimum) value critical mass m f crit 4.0 kg $$ {m}_f^{\mathrm{crit}}\left(4.0\ \mathrm{kg}\right) needed—at stoichiometric concentration air—for behave as VCE. To regard, any non-stoichiometric air or lower amount would decrease either flame Mach number M {M}_{\mathrm{f}} total energy, thus resulting negligible overpressure. sense, effects buoyancy, diffusivity, weather conditions dispersion should be taken into account. results are valid compressed cryogenic liquid tanks can sake distinction between flash fire VCE; hazard analysis production storage; more general risk assessment systems.