Experimental study on the mitigation of backdraft in compartment fires with water mist

In this paper, the results of a reduced-scale experimental test series using water mist to mitigate backdraft in compartment fires are presented. This reduced-scale compartment (1.2 m x 0.6 m x 0.6 m) was fitted with a variety of end opening geometries: middle-slot, upside-slot, downside-slot, door, window and vertical middle-slot, and ceiling opening geometries: slot and window. Water mist was generated by a downward-directed pressure nozzle that was operated at pressure of 0.2 MPa. Experimental variables included fuel flow rate, burn time, water mist injection time and mass, and opening geometries. Histories recorded prior to backdraft included upper layer temperatures, lower layer temperatures, and species concentration for oxygen, carbon dioxide and carbon monoxide. Data collected to quantify the backdraft included opening gas flow velocities and compartment pressures. The experimental results show that water mist is an effective mitigating tactic that is able to suppress backdraft in compartment fires primarily by means of diluting the gas in the compartment and reducing total hydrocarbons mass fraction, rather than by a thermal mechanism of cooling.