Study on Multi-Factor Coupling Simulation and Improving Fire Evacuation Strategies in Old Multi-Story Residential Buildings

As urbanization accelerates in China, existing multi-story residential buildings constructed between 1980 and 2000 face increasing fire risks due to high occupant density and outdated fire safety codes. This study develops a multi-factor coupling simulation framework integrating BIM, PyroSim (2020), and Pathfinder (2020) to evaluate fire evacuation safety. Results suggest that kitchens located farther from stairwell entrances tend to impose greater smoke temperature and visibility hazards. Alternating evacuations may outperform uniform platform-based strategies. Concentrating slow-moving occupants on lower floors may improve evacuation efficiency, while counterflow and returning behaviors tend to cause the greatest obstruction on middle floors (5th–7th stories). Multi-factor coupling analysis indicates nonlinear thresholds: maximum safe occupancy decreases from 6.0 to below 4.0 persons per household as building height increases from seven to nine stories; exit widths beyond 0.95 m yield diminishing returns; and critical stairwell obstacle sizes decrease from 0.6 m to 0.3 m as household density increases. Three retrofit strategies were examined: adding outdoor stairs achieved a safety margin of 71.2 s; adding evacuation platforms raised safe occupancy from 3.5 to 4.5 persons per household; and installing kitchen sprinklers reduced the smoke concentration in stairwells. These findings may provide a useful reference for fire safety retrofitting in existing multi-story residential buildings.