###### Abstract  
This study employs the FLACS code to analyze hydrogen leakage, vapor dispersion, and subsequent explosions. Utilizing pseudo-source models, a liquid pool model, and a hybrid model combining both, we investigate dispersion processes for varying leak mass flow rates (0.225 kg/s and 0.73 kg/s) in a large open space. We also evaluate explosion hazards based on overpressure and impulse effects on humans. The computational results, compared with experimental data, demonstrated reasonable hydrogen vapor cloud concentration predictions, especially aligned with the wind direction. For higher mass flow rate of 0.73 kg/s, the pseudo-source model exhibited the most reasonable predictive performance for locations near the leak source despite the hybrid model yielded similar results to the pseudo-source model, while the liquid pool model was more suitable for lower mass flow rate of 0.225 kg/s. Regarding explosion analyses using overpressure-impulse diagram, higher mass flow rates leaded to potentially fatal overpressure and impulse effects on humans. However, lower mass flow rates may cause severe endrum damage at the maximum overpressure point. liquid hydrogen (LH2); dispersion; explosion; pseudo-source model; liquid pool model; hydrogen leakage; CFD +
Footnote †: journal: Medical  
To address the safety issues and behavior of liquid hydrogen, extensive research has been conducted through both experimental [13; 14; 15; 16; 17; 18] and computational studies [19; 20; 21; 22; 23; 24] focused on dispersion and explosions resulting from liquid hydrogen leakage. A NASA study explored a significant liquid hydrogen leakage, simulating an accident in a large reservoir [13]. In total, 5.7 m\({}^{3}\) (-400 kg) of liquid hydrogen leaked; the effects were observed over time. A longer leakage time (i.e., lower leakage rate) was associated with slower combustible vapor cloud spread along the ground. HSL (Health and Safety Laboratory) conducted experiments on the behavior of liquid hydrogen when released at a rate of 60 L/min [14]. This study provided quantitative data on hydrogen concentration, liquid pool formation, and temperatures within the pool. The visible results of the hydrogen plumes demonstrated buoyant or non-buoyant behaviors of liquid and vapor phases of hydrogen based on the release conditions. Experiments were conducted to investigate the spreading and vaporization of liquid hydrogen, as well as the transient behavior of cryogenic liquids such as nitrogen and hydrogen after release onto water or solid ground [15]. The pool radius of these liquids after release was compared with a computer model, LAUV, developed based on shallow-layer differential equations of mass and momentum conservation. The simple computer model reasonably predicted the pool radius of liquid hydrogen. However, it did not solve all the governing equations related to liquid hydrogen leakage, resulting in limitations in predicting the concentration distribution of liquid hydrogen. The BAM (Federal Institute for Materials Research and Testing) conducted experiments to investigate the spread and evaporation of cryogenic hydrogen pools resulting from liquid hydrogen leakage, as well as the formation and dispersion of vapor clouds between buildings [16]. Additional computation was also conducted to investigate the behaviors of cryogenic hydrogen pools for the BAM's experiments. The size of the hydrogen pool, the ground temperature, and the evaporation rate were measured when liquid hydrogen leaked from one corner of two buildings 23.9 m apart at approximately 0.4 kg/s for 2 min. The computations were qualitatively and quantitatively compared with the experimental behavior of the condensed cold vapor cloud near the leakage source, as well as the effect of buoyancy on the cloud at distant sites. The buildings blocked the wind; the wind direction had an important role in vapor cloud spread. An experimental study of liquid hydrogen leakage was recently conducted by the FFI (Norwegian Defense Research Establishment) [17; 18].