Evidence for flame extinguishment by thermal mechanisms

This paper presents an analysis of experimental flame and detonation extinguishment data published by a number of authors, including those in a companion paper. The maximum effectiveness observed for each of five common dry chemicals at small particle diameters is shown to be related to heat extraction from the flame by active endothermic sinks—heat capacity, fusion, vaporization, and decomposition. Larger particles are more stable in the flame and the reduced level of effectiveness observed is due principally to the only active sink—heat capacity.Evidence is presented to support two propositions: first, that the strong chemical inhibiting effects exhibited by many substances in flame velocity studies are effectively confined to low-concentration regimes; and second, that regardless of chemical effects, diffusion flames of the type studied are largely extinguished by thermal or heat extraction mechanisms at extinguishant concentrations that are quantitatively predicted by a simple heat balance and a predictable limit temperature.

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