The introduction of hydrogen to the commercial market as alterative fuel brings up safety concerns. Its storage in liquid or cryo-compressed state to achieve gravimetric efficiency involves additional risks and their study is crucial. This work aims to investigate the behavior of cryogenic hydrogen release and to study the factors that greatly affect vapor dispersion. We focus on the effect of ambient humidity and air’s components (nitrogen and oxygen) freezing, in order to indentify the conditions under which these factors have considerable influence. The study reveals that humidity reduces conspicuously the longitudinal distance of the Lower Flammability Limit (LFL). Simulations with liquid methane release have been also performed and compared to the liquid hydrogen simulations, in order to detect the differences in the behavior of the two fuels as far as the humidity effect is concerned. It is shown that in methane spills the buoyancy effect in presence of humidity is much smaller than in hydrogen spills and almost negligible.