Fire Safety Science Digital Archive

HFC and FC agents were developed as replacements of halon 1301 (CF3Br), however, some fluorohydrocarbons decrease the lower flammability limits of combustible gases and vapors. To use trifluoromethane (CF3H), 1,1,1,2,3,3,3 heptafluoropropane (CF3CFHCF3), and perfluorobutane (C4F10) as the replacements safely in plants containing combustible vapors, cup-burner flame extinguishing concentrations of the agents, halon 1301, and nitrogen for n-heptane flames were investigated as functions of concentration of methane or methanol vapor in air. The following conclusions have been obtained: (1) when the air contains a combustible less than the lower flammability limit, blue flame appeared around n-heptane diffusion flame by addition of the HFC and FC agents in air. Such flame did not appear through the addition of CF3Br and nitrogen. (2) Methanol vapor in air increased the flame extinguishing concentrations of all agents when increasing the vapor concentration, while methane did not affect the flame extinguishing concentrations of all the agents until the blue flame was formed. (3) If a combustible vapor is mixed in the air of a space protected by a total flooding fire extinguishing system employing the HFC or FC agent, a design concentration determined by the flame extinguishing concentration is not always sufficient to extinguish fires in the space. An inerting concentration may be desirable for the design concentration in such case.