## 4 Conclusions  
We utilized the FLACS code to computationally analyze the dispersion of a hydrogen vapor cloud resulting from liquid hydrogen leakage in an FFI experiments. The dispersion process was investigated using a pseudo-source model, a liquid pool model, and a hybrid model that combines both. We compared the computational results with experimental data regarding hydrogen vapor cloud concentration and temperatures to evaluate the prediction performance of each model. Additionally, we explored the potential impact of the explosion on humans when the leaked liquid hydrogen was ignited. Here are the key findings:  
Hydrogen concentrations computed were relatively constant at all tested locations, except initially, while the experimental data showed significant variation over time. Predicted hydrogen concentrations were most accurate in the wind direction. For a leaked mass flow rate of 0.73 kg/s, computational results closely matched experimental concentrations at a distance of 30 m from the leak source. Predictions were reasonable even at a distance of 50 m. The pseudo-source model exhibited the best predictive performance at distances of 30 and 50 m despite the hybrid model producing similar results to the pseudo-source model. However, at a distance of 100 m, these models slightly overpredicted, whereas the liquid pool model provided a more accurate prediction. The computed temperatures for each distance demonstrated good prediction, roughly within the range of experimental variations. For a smaller leaked mass flow rate of 0.225 kg/s, the computations by the pseudo-source model and hybrid model overestimated the experimental concentrations while the liquid pool model predicted the hydrogen concentration reasonably at a distance of 30 m from the leak source. Predictions by three models were generally reasonable for distances of 50 and 100 m. The computations by the three models also demonstrated reasonable prediction of the experimental temperatures for all locations. From a computational perspective on practical issues, the pseudo-source model is recommended for locations near the leak source, particularly under relatively high leakage mass flow rates (m \(\geq\) 0.73 kg/s). Conversely, at a lower leakage flow rate condition, (m \(\leq\) 0.225 kg/s), the liquid pool model seemed more suitable in predicting the concentration of evaporated hydrogen up to 100 m. Additionally, for 0.73 kg/s \(\geq\) m \(\geq\) 0.225 kg/s, the hybrid model seemed to be reasonable. When applying the hybrid model, it is considered appropriate to adjust the fraction parameter \(\chi\) from 0 to 1.0, depending on whether the leaked mass flow rate is close to 0.73 kg/s or 0.225 kg/s. When utilizing the FLACS code for computational analysis of liquid hydrogen leakage and dispersion, applying the dispersion model based on the leaked mass flow rate condi  
Figure 14: Computed overpressures and impulses at selected locations for m = 0.225 and 0.73 kg/s. tions proposed in this study is deemed to yield more rational results in the computational analysis of liquid hydrogen leakage and dispersion from a practical perspective. However, only a small range of leaked mass flow rates was considered in this study. For much larger or smaller leaked mass flow rate conditions not covered in this study, further research is necessary to confirm the present results. Regarding explosion analyses, it is evident that larger mass flow rates (\(\dot{\text{m}}\) = 0.73 kg/s) can lead to maximum overpressure and impulse, potentially resulting in fatal outcomes. The impact of the explosion near the ignition source is less severe in this scenario. On the other hand, for lower mass flow rates (m = 0.225 kg/s), injuries near the ignition source are possible, and severe eardrum damage can occur at the maximum overpressure point. Conceptualization, SYC, C.B.O, K.H.D. and B.-LC; methodology, SYC, C.B.O., K.H.D. and B.-LC; validation, S.Y.C. and C.B.O; investigation, K.H.D. and B.-LC; writing--original draft preparation, S.Y.C. and C.B.O.