Mitigation of backdraft with water mist: A reduced-scale experimental study



Backdraft is a special fire behavior in a limited-ventilation building. It can develop from fires of either ordinary combustibles, or ignitable liquids that become oxygen-starved, yet continue to generate a fuel-rich environment. If abundant fresh air is abruptly supplied by opening a door or breaking a window, the hot gas in this vitiated building will rapidly combust and a fireball and blast wave will take place. Backdraft can occur abruptly with powerful destruction, which may cause fatalities and the collapse of buildings. In this paper, the results of a reduced-scale experimental test series using water mist to mitigate backdraft are presented. This reduced-scale compartment (length x width x height with 1.2 m x 0.6 m x 0.6 m) was fitted with a door end opening geometry (width x height with 0.2 m x 0.4 m). Water mist was generated by a downward-directed pressure nozzle operated at pressure of 0.2 MPa. The experimental results show that water mist is an effective mitigating tactic able to suppress backdraft in a building fire, primarily by means of reducing unburned fuel mass fraction, rather than by a thermal mechanism of cooling.