Experimental datasets for stair flow physics and numerical models, as well as human instability experiments.

This study explores how flood travels down stairways into underground spaces by combining physical experiments with numerical simulations. Physical experiments were conducted to measure the depth and velocity of typical stair flows and to identify stair types that reduce instability risks at different positions in metro stations. After calibrating the numerical model, we expanded the range of inflow conditions to further analyze the variations in water depth, velocity, and human instability along the stairs. Based on the observed flow patterns, an instability equation was derived for human exposed to jet flow regions. The analysis shows that taller and slimmer individuals are more likely to maintain stability and evacuate effectively under flood conditions. By integrating the theoretical and numerical results, we determine the critical water depth for safe adult male evacuation to be 0.302 m. These findings provide useful insights for improving the design and safety assessment of underground entrances in urban flooding scenarios.