Experimental and modelling study on smoke retaining effect of air curtain jet in urban utility tunnel fire

According to current Chinese fire standard, when a fire occur in an urban utility tunnel, the fire doors at both ends of the fireproof zone must be closed to prevent smoke from spreading to adjacent areas. Instead of utilizing traditional fire doors, this study presents a novel application of flexible air curtain jet to inhibit smoke dispersion. A 1/8-scaled tunnel with the size of 25 m (length) x 0.5 m (width) x 0.45 m (height) was used for tests. The effects of heat release rate, velocity and width of an air curtain jet on smoke retaining efficiency were studied. As the initial jet velocity increases, the axis of air curtain jet strongly deviates from the fire source. A theoretical model for the impact velocity at the bottom of a tunnel was established based on the empirical plane jet theory. The central axis trajectory of the air curtain jet, rather than the plane of the fire door, is used as the leakage surface to calculate the smoke blocking efficiency, thersby iproving the safety level. The threshold for the jet velocity of the air curtain was calculated using a smoke blocking efficiency of 70% as the standard for successful smoke blocking.