A Response-Time-Based Framework for Flood Safety Assessment in Subway Stations

Flood safety in subway stations depends not only on when floodwater reaches critical locations but also on whether evacuation routes remain usable long enough for evacuation to be completed. Conventional hydraulic outputs do not directly integrate these location- and route-based requirements. This study develops a response-time-based framework linking location-specific Available Safe Egress Time (ASET), hydraulic route-hazard screening, inundation-induced walking delay, and Required Safe Egress Time (RSET). Unlike depth- or ASET-only assessments, the framework evaluates evacuation-time feasibility and route walkability separately and interprets them jointly. It was tested through 36 simulations of a subway-station concourse varying entrance and elevator inflows and internal-door connectivity, with warning delay, evacuation demand, and exit capacity considered in RSET. Where the thresholds were reached, the office near the entrance inflows had an approximately 81% shorter wet-cell onset time and a 59% shorter ASET at 0.30 m than the more distant sump and drainage pump room. Higher and multiple inflows accelerated flood arrival, whereas door connectivity mainly affected subsequent water redistribution. In contrast, pump-room routes more frequently exceeded hydraulic walkability thresholds, and flooding increased travel time on the longest route to nearly four times its dry value. Baseline RSET more than doubled when the assumed evacuation demand increased tenfold to an upper-bound value that does not represent station occupancy. These findings distinguish time-critical from route-critical locations and show that a positive ASET–RSET balance does not ensure route walkability. The framework provides an operationally interpretable link between time-dependent hydraulic outputs and subway-station response planning.