Research of Fire Extinguishing Efficiency of Binary Mixtures of Pentafluoroethane (HFC-125) and Heptafluoropropane (HFC-227ea) with Nitrogen

Abstract

The problem of using gaseous extinguishants to eliminate fire sources is to inhibit the active radicals of the flame, but at the same time it is necessary to take into account the change in the concentration of oxygen. Therefore, the object of research was the value of the extinguishing concentrations of both individual extinguishants and binary mixtures of halocarbons and inert gases during the elimination of heptanes burning. It has been proven that when nitrogen was supplied, gaseous combustion products were diluted and the relative radiation intensity of hydroxyl radicals decreased to 80%; on the contrary, when pentafluoroethane (HFC-125) and heptafluoropropane (HFC-227ea) were supplied, the process of chemical inhibition of the combustion reaction took place which led to a significant reduction of the burning rate and, accordingly, the intensity of radiation of hydroxyl radicals by more than 4 times. The joint action of the inert gas and the combustion inhibitor in different ratios did not exceed the intensity of the radiation of hydroxyl radicals of the flame of the inhibitor itself. However, when an inert gas was introduced, the flame was being enriched with fuel and the number of hydroxyl radicals decreased, and the additional introduction of an inhibitor led to a more effective reduction of hydroxyl radicals in the flame. On the basis of the derived results of the experimental studies on the elimination of the fire source of a cup burner with binary mixtures of a halocarbon and an inert gas, it was established that a relatively small dilution of air with nitrogen led to a significant decrease in the extinguishing concentration of the combustion inhibitor. In particular, the extinguishing concentration of heptafluoropropane HFC227ea for extinguishing n-heptane can be reduced by 2.0 times if, by adding nitrogen, the concentration of oxygen in the air is reduced from 20.5 to 19% by volume, that is, by only 7% (relative). The practical value lies in the fact that the derived results of determining the extinguishing concentration of halocarbons, nitrogen and their binary mixtures make it possible to establish the conditions for the elimination of fire sources. © 2025 Trans Tech Publications Ltd, All Rights Reserved