The Concept and Measurement of Extinguishability as a Flammability Criterion

Burning experiments in enclosed spaces have shown that oxygen depletion leading to flame extinction occurs even in a relatively large volume of air, because convection is only partially effective in supplying air to a burning flame and removing products of combustion and pyrolysis. Quantitative evaluation of extinguishability through oxygen depletion determined under realistic burning conditions would, therefore, be a valuable indication of the hazard potential of a material. Accordingly, a method has been developed for establishing a characteristiol minimum-burning condition in terms of oxygen concentration which results in a more stringent criterion for the innate flammability of a material than the conventional oxygen index (O.I.) value. The TRI Flammability Analyzer is used to measure steady-state flame propagation rates at several oxygen concentrations high enough to support steady burning. Extrapolating the resultant linear burning rate oxygen concentration relation to zero burning rate-yields an intrinsie (O.I.)₀. With the analyzer. it is possible to determine intrinsic indices for the more common and vigorous upward directions of burning, and the upward indices obtained for a group of natural and synthetic fabrics, woven and knitted, are apprediably lower than the indices for the downward direcion. Indeed, all fabrics studied. except Nomex®. are found to be inherently capable of upward burning in air.