Flame Extinguishment Properties of Dry Chemicals: Extinction Weights for Small Diffusion Pan Fires and Additional Evidence for Flame Extinguishment by Thermal Mechanisms

An experimental study was made of the extinguishment of a small n-heptane diffusion flame (25.5 cm dia. pan) by a number of dry-chemical powders - KHCO sub(3), NH sub(4)H sub(2)PO sub(4), Na sub(2)B sub(4)O sub(7). 10H sub(2)O, (NH sub(4)) sub(2)SO sub(4), K sub(2)CO sub(3), K sub(4)Fe(CN) sub(6) . 3H sub(2)O, Na sub(2)CO sub(3), K sub(2)SO sub(4), NaCl, Na sub(2)C sub(2)O sub(4), K sub(2)C sub(2)O sub(4). H sub(2)O, and Monnex. The minimum weight of each required for flame extinction was determined as a function of particle size and sieve fraction. The sharp dis continuity previously observed super(1) is shown to be a common phenomenon. The experimental procedure was such that complete flame penetration was achieved for all particle sizes of each substance. Therefore, all results are latent, or maximum possible, effectiveness values. Flame extinguishment effectiveness is defined as the reciprocal of the extinction quantity.Substantial evidence, based on the new experimental data, is presented to support the propositions: (a) that particle sizes by sieve analysis below a limit size completely decom pose and/or vaporize in the flame; and (b) that the observed optimum effectiveness at small particle sizes is reliably predicted by thermal mechanisms super(2) with a flame heat bal ance and a predictable limit temperature.