A literature survey of the chemistry of flame inhibition

Abstract

Evidence is beginning to accumul a te indi cating that c. atalytic reco mbination of oxygen atoms may be the mechanism of extin cti on of flames by halo ge·nated ex tin gui shin g age nts. T he literature of flame inhibition and of oxygen ato m che mistry has b een examin ed to ascertain whether th e available data would support such a mechanism. Consid erable sustentative evidence was found .Kin e tic rate-consta nt data are not available co vering all reaction s of interest, but those that are reported indi cate that catalyti c recombination of oxygen atoms ca n probably compete s uccessfully with normal flam e processes which req uire them.

Molecular basis of flame inhibition

“…A number of reviews and surveys, concerned primarily with the chemical aspects of flame inhibition, have been made [8][9][10][11][12][13]. Discussions of the relationship of flame inhibition chemistry to fire extinguishment or fire proofing in general may be found in a number of comprehensive literature sources [2][3][4]14].…”

“…Some clues as to the nature of this interference are provided from macroscopic observations such as: (a) the effectiveness of halogens increases in the order fluorides ~ chlorides < bromides :: iodides; (b) CF3Br is about four times more effective than CF4 in preventing combustion of n/hexane air mixtures; (c) CF3Br is a good inhibitor in hydrocarbon-air flames but is mediocre in H2-air flames; (d) Br2 has very little effect on CO-0 2 flames but is effective when small amounts of H2 are introduced; and (e) in Br-substituted hydrocarbons and fluorocarbons the inhibitor effectiveness increases with the number of Br atom substitutions and, in certain instances, can be directly proportional to this number. For example, in a stoichiometric methaneair flame, the following CPv values are found: Bn [24], CH3Br [12], HBr [11] , CF3Br [17]. The high value for CF3Br seems anomalous and this has been attributed to a possible role of the CF 3 radical in flame inhibition.…”

“…Creitz [11] suggests that halogenated extinguishing agents act as catalytic agents for the recombination of oxygen atoms. Other workers have suggested that the halogens reduce the concentration of OH in the flame.…”

“…It should be noted that the apparent low effectiveness of CF3Br on the fuel side of diffusion flames (Creitz [11]) is explained by Friedman [10] simply as an artificial geometry effect, since the flame itself would be located on the air side of the stagnation point.…”

Rates of reaction of atomic oxygen with C2H3F, C2H3Cl, C2H3Br, 1,1‐C2H2F2, and 1,2‐C2H2F2

“…These reactions are of interest because of the possible role of halogen-containing compounds in flame inhibition [ 5 ] , as well as in understanding the effects of halogen substitution on olefin reactivity. We have therefore investigated the kinetics of the interaction of atomic oxygen with several halogen-substituted ethylenes.…”