Analysis of the influence of exhaust vent leakage on the efficiency of tunnel smoke evacuation

The ventilation section of an undersea road tunnel is extremely long. Air leakage from the exhaust vents significantly reduces the efficiency of the smoke exhaust system, which threatens the lives and safety of personnel. In this paper, a calculation model of exhaust vent leakage is established and the reliability of the calculation model is validated by field tests. Air leakage in the case tunnel reached 155.22 m³/s with a common type of exhaust vent, reducing the extraction efficiency of gas flow through smoke vents (extraction efficiency) by more than 40 %; the impact of air leakage cannot be ignored. The extraction efficiency of the exhaust vents is reduced from 89.59 % to 47.86 % as the leakage coefficient K₀ increases from 3 to 24 for the same smoke exhaust volume. As the number of opened smoke vents decreases, the extraction efficiency of the tunnel decreases. When the smoke vent spacing increases from 50 m to 90 m, the extraction efficiency increases from 52.51 % to 69.35 %. The proposed calculation model, which considers exhaust vent leakage, is important for evaluating the efficiency of the smoke exhaust system and will help to optimize the tunnel's fire safety design. An exhaust vent leakage prediction formula of the whole tunnel is also proposed.