Metro-connected underground commercial spaces present complex fire safety challenges due to enclosed layouts, dense pedestrian flows, shared evacuation routes, and diverse combustible materials. This study conducts a scenario-based fire evacuation assessment of a typical metro-connected underground commercial space in Nanjing, China, using coupled FDS–Pathfinder simulations. Three fuel scenarios were considered: polyurethane (PU), polyvinyl chloride (PVC), and a combined PU–PVC fuel scenario. Available safe egress time (ASET) was evaluated using visibility, CO concentration, and smoke temperature thresholds, while smoke-affected evacuation performance was assessed using a visibility-based walking speed attenuation model. The results show that visibility reached the critical threshold earlier than CO concentration and smoke temperature in all scenarios. The PU-only scenario produced the fastest smoke spread and the shortest ASET, with Stair 2 reaching the visibility threshold at 244 s. Under smoke-affected conditions, the total evacuation time increased from 364 s to 378 s. More importantly, a local ASET/RSET mismatch was identified at Stair 2, where 62 occupants remained near the node after the local ASET threshold was reached and local clearance was completed at approximately 250 s. By contrast, Stairs 4 and 7 retained safety margins of 133 s and 113 s, respectively. These findings indicate that evacuation safety in the simulated case was controlled not only by smoke-induced walking speed reduction, but also by route convergence, local stair capacity, and uneven exit utilization. The study provides case-based evidence for node-level fire evacuation assessment and evacuation management in metro-connected underground commercial spaces.

With the expansion of metro networks and the increasing integration of underground retail and transit facilities, metro-connected underground commercial spaces have become a common yet safety-sensitive urban form. In fire scenarios, evacuation in such environments is constrained not only by enclosure and limited egress capacity, but also by the interaction between smoke spread and strongly coupled pedestrian flows across connected zones. Existing studies have examined smoke propagation or evacuation performance in underground spaces, but fewer have explicitly addressed how smoke constraints reshape node-level safety and the relative effectiveness of different intervention strategies in metro-connected commercial environments. This study investigates smoke-constrained evacuation dynamics in a representative metro-connected underground commercial space in Nanjing, China. A coupled simulation framework integrating PyroSim and Pathfinder is employed to examine multiple fire-source scenarios. Available safe egress time (ASET) at critical evacuation nodes is assessed using tenability criteria including visibility, temperature, and CO concentration, and is then compared with evacuation performance to diagnose hazardous routes and node-level failures. On this basis, three intervention strategies—corridor widening, stair widening, and pedestrian diversion—are comparatively evaluated. The results show that, within the modeled case, visibility most frequently becomes the controlling tenability criterion, and stairway nodes tend to lose safety margins earlier than final exits. This indicates that smoke constraints in connected underground commercial environments can trigger an early node-failure process before overall exit capacity is exhausted. The comparison further shows that behavior-oriented pedestrian diversion is more effective than geometric enlargement alone in reducing critical-node pressure and improving system-level evacuation performance under the modeled conditions. Rather than proposing universally transferable design rules, this study provides case-grounded evidence on how smoke propagation and pedestrian convergence jointly shape evacuation vulnerability in metro-connected underground commercial spaces, and offers a structured basis for critical-node diagnosis and intervention comparison in similarly configured environments.