Large quantities of volatile and flammable liquids are used in extraction process, which are recognized as having a high fire potential. The flash point is one of the major physical properties used to determine the fire and explosion hazards of liquids. The flash point variation and the fire risk were studied for the extraction system. Experimental results were firstly presented for three ternary systems (diluent being phase 1: n-dodecane, kerosene or p-xylene; phase 2: water; phase modifier: n-butanol) and the binary pairs. The diluent is almost immiscible in water and the reverse also holds. It is assumed that only phase modifier distributes between two phases so that the partition ratio was used to estimate the equilibrium liquid composition in accordance with Nernst's distribution law. A simple and reliable flashpoint prediction model was developed based on the Liaw algorithm for binary miscible mixture, and the flash point prediction of the heterogeneous ternary system was reduced to that of a binary miscible system. The deviations between the predicted values and experimental data were mostly within 2.5 degrees C. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.