Impact of visibility level on stooped pedestrian movement characteristics and evacuation efficiency

In fire accidents, evacuation conditions are often severely compromised by the presence of smoke, which not only reduces visibility but also causes vertical height constraints, forcing pedestrians to evacuate in a stooped posture. However, previous studies mainly focused on the influence of visibility on upright pedestrian movement, little attention has been paid to the stooped pedestrian evacuation dynamics under different visibility levels. To address this gap, this study conducted controlled corridor evacuation experiments under varying visibility levels and interaction modes. The results revealed three typical behaviors of stooped pedestrians under limited visibility: exploration, wall-following, and connection behavior. As visibility decreases, individuals exhibit slower walking speeds and longer acceleration times. Gender and interaction mode were also found to significantly influence movement, with males generally walking faster than females. Besides, reduced visibility leads to lower corridor flow rates and increased time intervals, thereby disrupting flow continuity. From a spatial perspective, lower visibility resulted in tighter clustering of pedestrians and a higher risk of congestion. The findings are helpful for understanding the movement characteristics of stooped pedestrians at different visibility levels and provide a reference for the formulation of evacuation strategies in real scenarios such as fires.