Fire Safety Science Digital Archive

This paper presents a brief survey of the key aspects of flames spreading across various condensed combustibles, and a discussion on flame spread mechanisms. Flames can be divided into two types, diffusion flames and premixed flames. A diffusion flame spreads across the combustible surface by heating the combustible material, ahead of the leading flame edge, to the gasification temperature. The flammable gas ejected from the surface sustains the flame. Behaviour of the flame in this case is closely related to the gas movement near the leading flame edge. In contrast, a premixed flame propagates through a flammable mixture layer established over the combustibles. The flame propagation in this case depends on the characteristics of the flammable layer such as its thickness and the concentration profile across it. It is also shown that propagating flame behaviour is closely related to the gas movement near the leading flame edge. The reason is that the gas velocity field greatly influences the heat and mass transfer needed for flame spread or flame propagation. Therefore, data on the gas movement near the leading flame edge is desirable in studies aimed at understanding the mechanisms of flame spread or propagation.