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

Abstract

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 — KHCO₃, NH₄H₂PO₄, Na₂B₄O₇ . 10H₂O, (NH₄)₂SO₄, K₂CO₃, K₄Fe(CN)₆ . 3H₂O, Na₂CO₃, K₂SO₄, NaCl, Na₂C₂O₄, K₂C₂O₄ . H₂O, 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 observed¹ 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 mechanisms² with a flame heat bal ance and a predictable limit temperature.

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References

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