In a strongly exothermic reaction process, any cooling system failure can lead to a serious accident. The present paper investigates the developments in a polymerization reaction system when thermal runaway occurs. Temperature of polymerization is the key parameter of interest. In this work, a kinetic model of styrene polymerization was used to predict reactor temperature using Aspen Plus software. An adiabatic process of styrene polymerization was simulated, and the results indicate that the reactor temperature is able to reach 260 degrees C. When thermal runaway occurs, the degree of styrene polymerization is lower. Different conditions were employed to explore the influence of operating parameters. The results demonstrate that the higher the initial reaction temperature, the faster thermal runaway occurs, and that the greater the proportion of diluent is, the later the reactor reaches its T-MAX. (C) 2017 American Institute of Chemical Engineers