Fire Safety Science Digital Archive

This paper presents the results of a theoretical investigation designed to characterise the formation of toxic compounds in enclosure fires under suppression. The present work was primarily motivated by the need to gain insight into the mechanism of formation of those toxic compounds which are originated from the interaction between fires and gaseous suppression agents. For this purpose, detailed chemical kinetic modelling techniques were used to predict the generation of combustion products within the upper-layer of typical enclosure fires. Effects of the mixing phenomenon were investigated by considering two possible extremes using infinitely fast and infinitely slow mixing models. The heat loss variation was also studied under isothermal and adiabatic conditions. It is demonstrated that, the production of toxic compounds in the upper-layer is kinetically controlled. This is quite consistent with the production of other major species (e.g. CO) in the upper-layer. Calculations presented here show that the concentration of toxic compounds originated from halon extinguishing agents are much lower than those of halon replacement agents. For such agents due to the lack of significant chemical reaction inhibition, higher extinguishing concentration are required. As a result halon replacement agents produce higher levels of toxic compounds.