Extinction of counterflow diffusion flames with halon replacements

Extinction of counterflow diffusion flames on liquid fuels was investigated, to confirm the superiority of the counterflow diffusion flame over the cup burner method for measuring flame extinguishing concentrations of fire suppressants, and to examine the fire suppression effects of halon replacements. The flame extinguishing concentration for the counterflow flame was less sensitive to the burner size than that for the cup homer method. Furthermore, the flow velocity of the fuel vapor had no change when the suppressant concentration in the oxidizer mixture of the counterflow diffusion flame was varied, whereas it changed remarkably in the case of the clip burner flame. The flame extinguishing concentrations of nitrogen, carbon dioxide, halon 1301 (CF3Br), and three kinds of hydrofluorocarbons (HFC) and perfluorocarbon (FC) for n-heptane or ethanol counterflow flames were measured at various strain rates. Adiabatic flame temperatures at the extinction concentrations were calculated using the flame extinguishing concentrations measured for counterflow flames, assuming various equivalence ratios. The results suggest that HFC-23 (CHF3) suppression exhibits a higher contribution to the chemical suppression effect than other HFC or FC. Copyright (C) 1996 Elsevier Science Ltd.