In-situ experimental study on poison gas diffusion in subway station under different ventilation modes

To fully understand the influence of ventilation system on poison gas diffusion in subway station, full scale experiments were carried out in a subway station in Beijing. Three-dimensional ultrasonic anemometer was used to analyze the flow field in the station under mechanical ventilation and emergency ventilation. Then the gas diffusion and subsiding of heavy gas were studied based on the methods of SF6 release and sampling in chronological order, which provide suggestions for emergency response. The results showed that in emergency ventilation, the wind speed was greater, which was 1.2~2times that of mechanical ventilation. When SF6 diffused under mechanical ventilation, obvious settlement was observed, and SF6 was accumulated on the ground to form an area, concentration of which was higher than 50×10-6 for a long time. After the emergency ventilation was turned on, the settled SF6 accelerated upward transmission and quickly filled the whole station hall and the maximum concentration was more than 200×10-6. During emergency disposal, it was necessary to evacuate passengers to the upper or reverse area as soon as possible. It is strictly prohibited to open the emergency ventilation to avoid the diffusion of ground gas to the breathing area. © 2022, Editorial Board of China Environmental Science. All right reserved.