Wall fire behavior in an under-ventilated room

Abstract

An experimental setup has been designed and built to study, at a laboratory scale, the behavior of a wall fire in a semi-confined compartment both in naturally ventilated and vitiated (combustion products) atmospheres. A diffusion flame is stabilized along a vertical porous flat burner located at the rear of an enclosure. The combustion is supplied by injection of propane through the vertical burner surface. Air enters into the compartment by natural convection through a door, topped by a soffit, opposite the burner. After reaching a thermal steady state, the temperature field in the compartment is characterized. Then, the door is closed leaving only a horizontal free slot (0.06 m height) between the top of the door and the bottom of the soffit. The flame behavior completely changes, the intensity of the spontaneous flame emission decreases drastically and a weakly blue vertical flame leaves the burner surface and moves, at low velocity, through the chamber, up to the open slot. Visualizations of the flame and measurements of the temperature and main stable chemical species fields are performed in order to characterize the behavior of a flame referred as a ghosting flame. This flame displacement mode has been already observed in full-scale fires by Audouin (Fifth International Symposium on Fire Safety Science, 1997, Melbourne, p. 1261–1272). After the initial “flame propagation”, combustion can be stabilized at the room aperture that participates to the development of the fire outside the compartment. This work contributes to a better understanding of this phenomenon in order to prevent such a fire.