The global equivalence ratio concept and the formation mechanisms of carbon monoxide in enclosure fires

Abstract

This report summarizes a large number of investigations designed to characterize the formation of carbon monoxide (CO) in enclosure fires—the most important factor in fire deaths. It includes a review analysis of the studies which form the basis for the global equivalence ratio (GER) concept. Past and very recent (some as yet unpublished) investigations of CO formation in enclosure fires are reviewed. Based on the findings, two completely new mechanisms for the formation of CO, in addition to the quenching of a fire plume by a rich upper layer, which is described by the GER concept, are identified. The first is the result of reaction between rich flame gases and air which is entrained directly into the upper layer of an enclosure fire. Detailed chemical-kinetic modeling studies have demonstrated that CO will be generated by these reactions. The second is due to the direct generation of CO during the pyrolysis of oxygenated polymers (such as wood) which are located in highly vitiated, high-temperature upper layers. The findings of these studies form the basis of an analysis that provides the guidelines for when the use of the GER concept is appropriate for predicting CO formation in enclosure fires. It is concluded that there are limited conditions for which such use is justified. Unfortunately, these conditions do not include the types of fires which are responsible for the majority of fire deaths in building fires.