Fire Safety Science Digital Archive

Detailed mappings are presented of extinction coefficient and flow fields at the base region of a heptane medium-scale pool fire during the addition of a water mist. These mappings were obtained by using, on the one hand, an original methodology coupling extinction measurements at two wavelengths and permitting the separation of the respective contribution of soot particles and water droplets and, on the other hand, PIV measurements and processing permitting the determination of their flow velocity patterns. This work results in information about the interaction between mist and liquid pool fires and about the resulting structure at the base of the flame. The customarily described well defined structure of the fire flame does not exist any longer. It is observed that the size and shape vary randomly and continuously and that frequent clearances of the liquid surface, due to sudden and short vaporization periods, occur followed by extinguishment or flashback. This behavior suggests that extinguishment is achieved by total clearance of this surface rather than from the reduction of the burning rate. The results obtained could also be used, in future work, as a data base for the prediction of the change of the radiation heat flux to the fuel surface, problem still not well known and studied. However, it is important to realize that the measurements are not instantaneous and that they provide only averaged values when the measured properties are affected by the flame disruption.