Limits to the Effectiveness of Metal-Containing Fire Suppressants. Final Technical Report (NISTIR 7177)

This report reviews the literature on metal inhibition of flames and identifies metal species with potential as fire suppressant additives. To provide a basis for discussion, the detailed mechanism of inhibition of iron is reviewed, and the reasons for its loss of effectiveness are described. The demonstrated flame inhibiting properties of other metals is then discussed, followed by a description of the potential loss of effectiveness for these other metals. The production ban on the widely used and effective halon fire suppressants due to their ozone depletion potential, has motivated an extensive search for replacements. Metal containing compounds have attracted attention- especially for unoccupied spaces-because of their extraordinary effectiveness in some configurations. For example, Fe(CO)5 has been found to be up to eighty times more effective than CF3Br at reducing the overall reaction rate in premixed methane-air flames, when added at low concentration. Unfortunately, it has also been found to produce condensed-phase particles which reduce its effectiveness for co-flow diffusion flames. Hence, it is of interest to identify other metal compounds which may be strong flame inhibitors and then to assess their potential for loss of effectiveness through condensation. To achieve this goal, the present report provides background on current understanding of metal inhibition of flames, identifying metals with fire suppression potential. The inhibition mechanism of the iron is described, and the followed by a description of the reasons why it losses its effectiveness in some flame systems. The equivalent flame inhibiting species of other metal agents is then discussed, and evidence for any potential loss of effectiveness for these other metals is assembled and discussed.