## 5 Conclusions  
In this study, the investigation of inundation in subway platforms was conducted to find the safety criteria for citizens against flooding. The inundation characteristics and safety areas were analyzed and validated in a subway station model using experimental inundation depth measurements and numerical simulations. Then, by utilizing five risk evaluation indices--including specific force (\(M_{0}\)), Flood Hazard Degree (\(FD\)), Flood Intensity Factors (\(FIFF\)), toppling velocity (\(U_{\text{ct}}\)), and sliding velocity (\(U_{\text{cs}}\))--the effects of increased inflow on water velocity and depth were studied using the simulation. The flood risk assessment analysis results show that assessments using \(M_{0}\) could increase uncertainty by broadening the evaluation of risky areas compared to other indices. The effects on human models on and near the stairways using pressure and drag force were also presented. With this research, simulations with various conditions showed that hydrodynamic characteristics and their effects on human stability in a flooding subway area can alter  
Figure 15: Flood risk range according to safety indices: the solid lines represent the range of minimum and maximum values, while the dashed line indicates the average value.  
over time. Overall, these risk assessments would provide a criterion for flood situations in subway stations.  
The utilization of inundation simulation results of subways in this research can be used by engineers for identifying vulnerable points in the subway infrastructure. By understanding how water could flow and accumulate during floods, engineers can design better drainage systems for the subways. Also, city planners can plan risk mitigation strategies by using inundation simulations for comprehensive flood risk management plans. Emergency response teams could use simulation models to predict the progression of flooding and make informed decisions on how to manage evacuations and prepare detailed plans for emergency personnel deployment. The advantages of the proposed simulation and research are that 3D models can accurately capture the complex flow patterns within subway systems, especially in vertical areas such as stairs. Also, using human models based on real data can allow better prediction of force applied to humans in flooding situations. 3D models can handle complex interactions between water and air in underground systems, which is particularly useful for simulating scenarios where water levels change rapidly such as fast flooding. However, the simulation results presented in this study have the limitation of only analyzing one human model due to the computation time and complexity of the geometry setup. In actual disaster situations, evacuation by crowds occurs, so flood risk analysis for these situations is necessary.  
Future research could involve using laboratory experiments for risk assessment on crowd evacuation and temporal/spatial variation of flood risk evaluation and its simulation validation. Also, additional analysis on uncertainty regarding flood risk assessment and evacuation time could be conducted.  
Conceptualization, J.S., D.S.R. and I.P.; methodology, J.S. and I.P.; software, J.S.; validation, J.S. and I.P.; writing--original draft preparation, J.S., D.S.R. and I.P.; writing--review and editing, J.S. and I.P.; project administration, I.P. and J.S.; funding acquisition, I.P. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the Korea Agency for Infrastructure Technology Advancement (KAIA) grant funded by the Ministry of Land, Infrastructure and Transport (Grant No. RS-2023-00238018).  
Not applicable.  
The data presented in this study will be shared by the authors if requested.  
This research was supported by the Korea Agency for Infrastructure Technology Advancement (KAIA) grant funded by the Ministry of Land, Infrastructure and Transport.  
The authors declare no conflicts of interest.