Investigating the influence of outdoor temperature variations on fire-induced smoke behavior in an atrium-type underground metro station using hybrid ventilation systems

Underground metro systems are expanding rapidly worldwide, necessitating research on energy-efficient ventilation systems, fire safety, and smoke control. This study investigates the optimisation of hybrid mechanical-natural ventilation for smoke control in complex metro stations. Full-scale winter/summer experiments and numerical simulations examined a double-deck atrium-type station. Results demonstrate the atrium fires are more significantly impacted by outdoor temperature variations versus concourse/platform fires, with a 70 K versus 30 K temperature rise above the fire respectively. The heat of the gathered high-temperature smoke inside the atrium can reach up to 900 K under a 5 MW train fire energy release. The dimensionless Archimedes number (Ar) defines the ratio of thermal buoyancy to gravitational forces. Cold exterior winter air (Ar<1) entering via the atrium ceiling openings restricted vertical smoke diffusion, enabling enhanced lateral propagation. With rising outdoor temperatures from -20 degrees C to 10 degrees C (Ar<1), the natural smoke extraction efficiency increased from 0 to 18 %, coupled with vertical airflow velocities accelerating from -3.5 m/s to 1.5 m/s. When outdoor temperatures were between 10 degrees C and 40 degrees C (Ar>1), airflow velocity only changed slightly. Empirical models predict internal temperature profiles as a function of external meteorology. The findings provide crucial engineering insights into integrating weather data and adaptable ventilation protocols for scenario-based smoke prevention/mitigation. Further work should examine seasonal variations beyond the tested -20-40 degrees C range. Overall, considering outdoor climate effects allows 30 % optimisation of hybrid ventilation systems for fire safety in underground metro stations. This study promotes technological advances in energy-efficient transport infrastructure resilience.