Fire Safety Science Digital Archive

Flame size and heat flux correlations were obtained by experiments for circular turbulent flame sheets developing from a downward injection source beneath an unconfined inert ceiling, and are compared against those for one-dimensional ceiling flames. These correlations show proportionality of the flame sheet area to heat release rate and the representation of flame heat transfer as a function of the distance from the source normalised by flame length. Heat release rate per unit flame sheet area in circular flames is found to be significantly smaller than that in one-dimensional flames. It suggests a weaker entrainment of ambient air to circular flames than to one-dimensional flames. Total heat flux to the ceiling surface from the flame sheet is less than 30 kW/m² and is not enough to accelerate flame spread. This suggests the importance of preheating of a combustible ceiling by a hot gas layer for the fast fire spread generally observed in real and experimental room fires. Dimensional analysis based on the experimental results suggests the proportionality of horizontal velocity to the distance from the upstream end of the burning surface, and faster velocity in one-dimensional flames than in circular flames.