On the Critical Air Velocity for Fire Smoke Control in a Curved Tunnel

Using the construction of double-spiral tunnels as an example, this paper discusses the critical air velocity and the smoke-flow law in a curved tunnel with a diameter of 600 m determined by numerical calculations. The results given by the numerical calculations agree well with those given by a fire test in the Memorial tunnel: the critical air velocity for fire smoke control is 2.5 m/s for a fire of 10 MW in the curved tunnel; smoke backflow occurs, and the backflow length and thickness increase significantly, when the ventilation velocity decreases; the deflection angle of the flame and the maximum temperature of the vault increase with an increase of the ventilation velocity; and at the downstream of a fire, the smoke around the fire source forms an asymmetric distribution and is followed by an obviously layered smoke.