Smoke Exhaust Technology of Different Opening State of Smoke Vent in Mawan Tunnel

In order to study the effect of the tunnel smoke exhaust mode and the opening state of the smoke Vent on the smoke exhaust efficiency during the fire, the smoke exhaust characteristics and smoke exhaust efficiency of the Mawan underwater shield tunnel were analyzed. Firstly, through the theoretical analysis and fire dynamics simulator FDS, the critical wind speed of the longitudinal ventilation and smoke exhaust mode and the optimal smoke exhausting amount of the key ventilation and smoke exhaust mode are calculated. Secondly, a variety of working conditions are set based on different opening state of the smoke Vent. And the smoke height, spread length, visibility at the height of the human eye, CO volume concentration, wind speed at the exhaust port and smoke exhaust efficiency were studied. The results show that: (1) the critical wind speed of the Mawan Underwater Shield Tunnel is 4.5 m/s. When the key smoke evacuation method is adopted, the optimal air volume of smoke exhaust for opening the upstream and downstream exhaust vents is 290 m³/s, and the value for opening the downstream exhaust vents is 410 m³/s. (2) When the upstream and downstream exhaust vents are opened, timely opening the exhaust vents directly above the fire source can ensure that the visibility of the human eye is higher than 10 m, and the CO concentration exceeds the human tolerance limit only in the range of 200 m upstream and downstream of the fire source, and the maximum value is only 450 ppm. The smoke height rises within the range of nearly 100 m in the upstream direction of the fire source, the smoke spread distance is shortened. (3) When the upstream and downstream exhaust vents are opened, and the exhaust vents at the top of the fire point are opened in time, the overall exhaust efficiency is higher than when the exhaust vents at the top of the fire point are not opened. When only the downstream exhaust vents are opened, the opposite is true. (4) In combination with the personnel escape index, when a fire occurs, the key smoke evacuation method should be adopted, the upstream and downstream exhaust vents should be opened, and the nearest exhaust vent of the fire point should be opened in time.