Optimization of tunnel ventilation system by modeling changes in air flow rate and carbon monoxide concentration...

This study investigates the optimization of tunnel ventilation during fire scenarios using Fire Dynamics Simulator (FDS)-based numerical modeling for a Shanghai Metro tunnel section. The model evaluates temperature evolution, heat release rate, carbon monoxide concentration, and the airflow required to maintain structural safety and support sprinkler-assisted fire suppression. The results showed that the inlet airflow rate strongly influenced the thermal and gas-dynamic conditions in the tunnel: the gas temperature varied from 420 to 720 °C, the heat release rate ranged from 2 to 9 MW, and the peak CO concentration at the tunnel outlet reached approximately 1500 ppmv during the most intense fire stage. Based on the airflow-temperature relationship, two critical control thresholds were identified. Mechanical ventilation should be activated when the tunnel temperature reaches 138 °C, whereas intensified ventilation and sprinkler-assisted suppression become necessary near 525 °C. The calculations further showed that the required air supply increases by approximately 3.6 times only at the critical stage, which indicates that sequential activation of ventilation and sprinkler subsystems can avoid unnecessary full-capacity operation during earlier fire phases and thus improve the energy efficiency of tunnel emergency management. The proposed control logic provides a practical basis for coordinating ventilation and sprinkler operation while maintaining target air-quality and structural-protection conditions.