###### Abstract
Liquid pool formation and evaporation, vapor cloud dispersion, and hydrogen concentrations in vapor clouds were investigated when liquid hydrogen leaked into an external space through a 1-inch-diameter pipe. Explosion tests were conducted in the open under defined conditions. Liquid hydrogen leakage and explosions in a machine room were also evaluated. The hydrogen vapor concentrations after leakage were measured at various locations and times. Explosion overpressures were also assessed for the explosion in a closed space. Additionally, computational studies are important; liquid hydrogen evaporation has not been adequately explored. The experiment of NASA was computationally analyzed in terms of the leakage rate and duration, as well as the wind speed [19]. In their study, a liquid pool model was employed in FLACS computations for simulating large-scale liquid hydrogen pool leakages, considering pool size. The computations were conducted for leakage rates of 1.67, 9.5, and 10.3 kg/s. They investigated the downwind hazardous distance and the distribution of flammable concentrations in the hydrogen-air clouds formed under different leakage rate conditions. The results indicated that the leakage rate, duration, and wind speed all influence the distribution of hydrogen vapor clouds. Moreover, the release rate and duration had a greater impact on the shape of the flammable concentration distribution compared to wind speed. The dynamics of liquid hydrogen release were computationally investigated, and the modeling process for liquid hydrogen release was described [20]. The study demonstrated that the pseudo-source approach for liquid hydrogen release yielded reasonable predictions for the temperature near the jet exit by appropriately selecting the release velocity. However,it overestimated the distance to reach a 15% hydrogen concentration compared to the experimental results. A computational study was conducted on the leakage and explosion in a liquid hydrogen refueling station in China [21]. A pseudo-source model was established to compute the liquid hydrogen leakage. The optimal mass fractions for the pseudo-source model at the leakage exit boundary in the computations were determined by comparing them with the experimental temperature distribution. The distributions of hydrogen concentration, temperature, and overpressure during the explosion were investigated using the optimized pseudo-source model. CFD was employed to simulate the dispersion of liquid hydrogen for the experiment conducted by HSL [22]. This study investigated several factors that greatly influence modeling of the dispersion from the leaked liquid hydrogen. The computations with a homogeneous equilibrium model (HEM) were compared with those with a non-homogeneous equilibrium model (NHEM) to consider the slip effects of the non-vapor phase. The prediction performance for the steady temperatures around the leakage source obtained by those two models was evaluated by comparing with the HSL experiments. A different HEM for handling liquid hydrogen release through two-phase flashing jets and pool spills has been developed as part of the FLACS model [23]. The model treats the liquid hydrogen release as two-phase flows in local thermal and kinematic equilibrium. The prediction performance for temperatures using the HEM was validated by comparing them with previous experiments. However, the HEM for the FLACS code is not yet available. Recently, CFD studies were conducted for large-scale liquid hydrogen release [18; 24]. In these studies, a pseudo-source model with limited air entrainment was utilized in the computations, and the distributions of hydrogen concentration and explosion overpressure were compared with selected FFI experiments [17]. The computational approach represented the very cold liquid hydrogen leak scenarios properly in the near field, and reproduced concentrations and temperatures observed in the experiments reasonably.