Flame Inhibition of Current Fire Extinguishers and of Potential Substitutes

Abstract

The replacement of the commonly used fire extinguishers CF 3 Br and CF 2 ClBr has prompted the search for new inhibitors that are less damaging to the ozone layer but as active to inhibit combustion. In this paper, four approaches are considered : 1) Influence of additives on the burning velocities, 2) Structures of inhibited flame , 3) Chemi-ionization in flames with inhibitors, 4) Numerical modeling of inhibited flame systems. From the data, a simplified chemical inhibition mechanism is discussed and the role of the bromine chemistry in inhibition is emphasized. All substitutes suggested so far that are harmless to the ozone layer are not efficient enough to replace halon 1301.After the discovery of the probable contribution of chlorofluorocarbons to stratospheric ozone depletion in 1974 by Molina and Rowland [1], the scientific debate led to the regulation of most of these compounds in the Montreal Protocol [2]. Replacement of the commonly employed fire extinguishers CF 3 Br and CF 2 ClBr has been required also because their production was discontinued as of January 1994. The search became essential for other compounds less damaging to the ozone layer but active as flame extinguishers. To move beyond experiments which essentially check the macroscopic phenomena of fire extinction as a function of the amount of extinguisher added [3], more detailed studies have been conducted in order to reach a better understanding of the chemical and physical processes responsible for flame inhibition. Four approaches have been used: 1) The influence of added compounds on the burning velocities of several flammable mixtures, 2) The analysis of inhibited flame structures, 3) The chemi-ionisation in flames seeded with inhibitors, 4) The numerical modeling of flame systems.