Flame Inhibition by CF₃CHCl₂ (HCFC-123)

A kinetic model is suggested for hydrocarbon/air flame propagation with addition of hydrochloroflurocarbon (HCFC) fire suppressant, encompassing the combined chemistry of fluorine- and chlorine-containing species. Calculated burning velocities using the kinetic model are in good agreement with available experimental burning velocity data for CF₃Cl, CF₂Cl₂, or CFCl₃ added to CO/H₂/O₂/Ar flames. The agent CF₃CHCl₂ is more effective than C₂HF₅, and reaction pathway analysis shows that the inhibition effect of chlorine reactions is greater than that of fluorine. The main reactions of the chlorine inhibition cycle are H+HCl=H₂+Cl, OH+HCl=H₂O+Cl, Cl+CH₄=HCl+CH₃, Cl+HCO=HCl+CO, and Cl+CH₂O=HCl+HCO. The inhibition effect of CF₃CHCl₂ is largely the result of competing reactions of chlorine-containing species with hydrogen (and other radical pool) species, decreasing the rate of the chain-branching reaction H+O₂, with additional effects from substitution of the reactive chain-branching radicals for less reactive fluorine- and chlorine-containing radicals.