where 𝑥 𝑖 is the molar fraction of component i in the liquid phase, n is the number of flammable components, 𝛾 𝑖 is the activity coefficient of component i, 𝑃 𝑖 𝑠𝑎𝑡 is the vapor pressure of pure component i, and 𝑃 𝑖,𝑓𝑝 𝑠𝑎𝑡 is the vapor pressure of pure component i at its FP temperature. Since both the activity coefficient and vapor pressure depend on the temperature, the FP can be determined iteratively.