## 3 Results
### Flood Hazard Area Analysis  
To analyze where dangerous and safe areas in the model are located and their degree of safety, various indices have been used to evaluate how safe certain areas are. Figure 6 shows the result of the estimation of specific force from the Q1 and Q2 inflow cases. In the lower inflow case, the specific force had high values over 0.125 m\({}^{2}\) nearby and below the stairs which is a value that causes difficulty in evacuation. As the flow increased by almost two times in Figure 6b compared to Figure 6a, the areas considered unsafe by specific force criteria have enlarged showing most of the area near the flooded stairs and areas reaching the outflow area are over the limit of 0.125 m\({}^{2}\) and reach values near 0.4, showing the effects of higher flowrate to specific force estimated values. Other safety criteria such as the Flood Hazard Degree (_FD_) and Flood Intensity Factor (_FIF_) were also applied to the Q2 inflow case in Figure 7. Flood Hazard Degree values over 2.0 are known to be 'Extreme' hazards and values of _FD_ over 2 are shown right below the stairs and into the central area in Figure 7a. Flood Intensity Factors over 1.5 are considered'serious' hazards which are shown clearly in the central areas of Figure 7b. For the evaluation of safety in the entire model, a method using the ratio (%) of the flooding risk for each simulation case compared to the maximum risk in Figure 8 by time of inflow  
Figure 4: Temporal variations of depth-averaged velocity results from simulation. Figure 5: Temporal variations of inundation depth results from simulation. was adopted. The calculated and normalized values were compared using a single value; in the case of a specific force in Figure 8a, areas above values of 0.125 m\({}^{2}\) were considered to be flood risk areas, and the ratio of the flood risk areas divided by the total area was calculated. In the case of _FD_, it used an evaluation method where after assigning the safety interval states with 0 to 3 points (0 for \"Low\", 1 for \"Moderate\", 2 for \"Significant\", 3 for \"Extreme\"), the sum of the points times the assigned area was divided by the maximum risk which was 3 points for all the areas. _FIF_ was evaluated in a similar way; after evaluating the intervals in 3 states from 0 to 2 points, the maximum risk value of 2 points for all areas was divided. This method assumes the risk ratio value compared to the highest danger situation in the evaluation area. Figure 6: Spatial variations of specific force calculated from simulation. Figure 7: Result of estimation of Flood Hazard Degree and Flood Intensity. Figure 8 shows flood risk values increasing by the time of inflow in most situations, however, some cases such as Q3 specific force in Figure 8a and Q2 _FD_ and _FIF_ in Figure 8b,c showed that some flood risk values increased until 30 s but became lower in 40 s. This result somewhat matches the velocity and depth results shown in Figures 4 and 5, where the flow would collide at the center of the model, and the inundation depth would show an instantaneous increase and then later converge into a lower steady state as the water would reach the center area for outflow. This shows some insight that continuous inflow does not directly lead to lower safety in underground stations, since some structures such as the model used in this study have the flow leading to the outflow (originally stairs to the lower floor B2F) causing lower inundation depth as time passes. This could be a characteristic of underground subway stations with certain types of stairways and passages. Additional safety criteria using the risk of sliding and toppling stability using Equations (3) and (4) according to former research [9] are estimated in Figures 9 and 10. The variables for height and weight used average values targeting 60-year old females. Figure 9a shows the estimated value of sliding critical velocity minus simulated velocity at Q3.