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Prediction of HF Formation During Suppression.


pdf icon Prediction of HF Formation During Suppression. (5704 K)
Linteris, G. T.; Gmurczyk, G. W.

NIST SP 890; Volume 2; Section 10; November 1995.

Fire Suppression System Performance of Alternative Agents in Aircraft Engine and Dry Bay Laboratory Simulations. Volume 2, Gann, R. G., Editor(s), 201-318 pp, 1995.

Available from:

National Technical Information Service
Order number: PB96-117783

Keywords:

fire suppression; aircraft engines; nacelle fires; simulation; halon 1301; halon alternatives; fire suppression; premixed flames; flame structure; burning velocity; experiments; large scale fire tests

Abstract:

The acid gases hydrogen fluoride, hydrogen chloride, and hydrogen bromide (HX, where X denotes a halogen), are thought to be the most damaging and dangerous of the potential decomposition products, and much study has been devoted to determining the amounts of these chemicals formed during fire suppression by CF3Br and halon alternatives. While CF3Br is known to readily decompose to form HF, HBr, and COF2 in laboratory premixed and diffusion flames and in larger scale fires, the amounts were not considered to be a major threat compared to that of the fire itself. The alternative agents have been found to produce significantly more acid gas than CF3Br, and consequently, there exists a need to understand and predict the mechanisms of formation of acid gases in laboratory flames, and ultimately, suppressed fires. The goal of this project is to develop an ability to predict the quantity of HF formed during suppression of aircraft fires. In order to understand the formation rates of acid gases in dry bay and engine nacelle fires it is necessary to examine the thermodynamics and chemical kinetics relevant to the formation of the acid gases as well as the effects of the flow field and mixing on the chemistry. An engine nacelle fire may be similar to a steady turbulent spray diffusion flame, whereas a dry bay fire may resemble a rapidly advancing turbulent premixed flame. Because suppression of the dry bay fires occurs in a time of about 100 ms, it is also necessary to consider transient effects on the acid gas formation. The formation of toxic and corrosive by-products in flames/fires inhibited by halogenated hydrocarbons is controlled by transport rates of the agent into the flame, chemical kinetic rates, or equilibrium thermodynamics. These factors are affected by the fuel type, local mixture composition, inhibitor type and concentration, and the characteristics of the flow field such as mixing rate, strain rate, and stabilization mechanism in the case of laboratory burner flames. The approach taken in the present work is to examine the HF production in the fire, for a range of conditions.