This study deals with safety aspects of batch reactors for styrene suspension polymerization. Polymerization is known to be the most frequent cause of thermal runaway incidents in the industrial chemical processes. Two sorts of safety problems have been studied in this work. The first one is related to an influence of process parameters on the thermal behavior of the well-mixed polymerization reactor. With regard to this part of the work the modeling results have been presented in a form of the maximum reaction temperature maps, which allow for choosing the safe process conditions. The second one is related to a stirrer malfunction in the suspension polymerization reactor. As the computational fluid dynamics (CFD) simulations have shown, thermal runaway starts when the mixing problems occur even if an emergency cooling is applied.