The extinction of hydrocarbon flames based on the heat‐absorption processes which occur in them

Abstract

An empirical relation has been developed which correlates and predicts the 6re-suppression effectiveness of a wide variety of gaseous, liquid and solid agents. The flame-extinguisbment model is based on the premise that extinction is dominated by heat-absorption processes and that a flame is extinguished when suBcient heat has been removed by the extinguishant to reduce the temperature to a limit value. This limit is the minimum temperature at which the effective rate of the combustion reactions is s d a e n t to maintain flamepropagation, and it depends in a predictable way on the properties of the suppressant and flame system. The heat-balance equation describing tbis is derived in two stages. In the first, a preliminary equation is obtained by considering only those substances which are thermally stable and act only as heat-capacity sinks. In the second, the equation is generalized by consideration of all endothermic reaction sinks, e.g. vaporization, dissociation and decomposition. The general equation correlates most of the extinction data found in the literature. The results suggest that for most substances the extinguishing capacity is related to heat-extraction and that many of the effects previously attributed to chemical mechanisms may be thermodynamic in nature rather than kinetic.

Extinguishment of Class B Flames by Thermal Mechanisms; Principles Underlying a Comprehensive Theory; Prediction of Flame Extinguishing Effectiveness

“…Selection of data in this article is largely based on the very consistent set of ambient results by Hirst The true limit temperature for each gaseous extinguishant is based on its heat of formation at 298 K (Equation 1). The limit is that temperature at which the total quenching or heat-absorption sinks contributed by an agent at its experimental extinction concentration is equal to the theoretical excess heat in the flame.…”

“…The adiabatic flame heat balance as expressed by Equation 1 is derived specifically for stoichiometric fuel-air flames. This type of equation without the agent's reaction sinks is commonly used to compute adiabatic temperatures or mixture compositions for various limit flames.…”

“…The accurate computation of the theoretical excess flame heat, the quantity represented by the right side of Equation 1, was important to this study. The excess heat was computed from 1400 to 2250 K for several common hydrocarbon-air flames (Table 1).…”

A Unified Model of Fire Suppression by

“…Including the heat of dissociation, AHA, in Equation 9 yields ' Including dissociation has no effect on Equation 11 Ewing, Hughes, and Carhart9 have shown that the extinction of gaseous and liquid fuels in air by dry chemical agents can be predicted using TAFJSL) = 2165 K if the agent's heat capacity and heat of dissociation are included. They further found that the performance of bromine containing halons can be predicted using TAFJSL) = 2015 K and the agent's heat capacity.…”

Extinguishment of Diffusion Flames of Polymeric Materials by Halon 1301

“…It also appears that critical condition for flame extinction occurs when combustion efficiency is reduced below about 0.40. Ewing, Hughes, and Carhart [10] have developed an empirical relationship which correlates and predicts the fire suppression effectiveness of a wide variety of gases, liquid, and solid agents. Sheinson, Penner-Hahn, and Indritz [11] have examined the physical and chemical action of fire suppressants to provide guidance in selecting alternative fire suppressants to replace ozone layer depleting Halons.…”