Flame-extinguishing concentrations and peak concentrations of N-2, Ar, CO2 and their mixtures for hydrocarbon fuels

Fire-extinguishing efficiency of inert gas mixtures was investigated by measuring flame-extinguishing concentrations and peak concentrations for hydrocarbon fuels, because new fire-extinguishing agents composed of inert gas mixtures have been developed as halon alternatives. The flame-extinguishing concentrations of nitrogen, argon, carbon dioxide and their mixtures for n-heptane were measured with the FRI glass cup burner. The peak concentrations of the agents for methane-air and propane-air mixtures were also measured with the tubular flame burner. Chemical equilibrium calculations showed that the adiabatic flame temperatures of the cup burner flames at the extinction condition were almost constant for all the agents. The adiabatic flame temperatures at the flammability limit of the tubular flame for each fuel were also independent of the inert gas agent if the mixtures had the same equivalence ratio. The flame-extinguishing concentrations of the inert gas mixtures were predicted by a simple equation averaging over the flame-extinguishing concentrations of all component gases weighted by mole fraction. The equation has the same form as Le Chatelier's law. For the flammability limits of the hydrocarbon-air mixtures, the same relation was also recognized in the effect of the mixed agents. The facts show clearly that this simple equation for the flame extinction concentrations is useful to estimate the fire suppression efficiency of any mixed agents of the inert gases. At the same time, it appears that the flame-extinguishing concentrations and the flammability limits reported in the paper are consistent. (C) 1997 Elsevier Science Ltd.