The presented work is a part of studies carried out to develop a practical method to prevent runaway events in chemical reactors. The use of computational fluid dynamics (CFD) techniques is proposed here to indicate in advance the local hot-spots in the reaction mixture, so as to elaborate an efficient and sensitive method for early warning detection of runaway. The CFD method has been chosen to support, elaborated by Bosch et al. (Comput. Chem. Eng. 28 (2004) 527), the on-line runaway detection method in batch reactors, which is based on the divergence criterion. Series of CFD simulations have been executed for two exothermic reactions, being the esterification reaction of the 2-butanol and the propionic anhydrite catalysed by the sulphuric acid (homogeneous system) and the hydrolysis of the propionic anhydrite catalysed by the sulphuric acid (heterogeneous system). For both the considered reactions the results of calculations have been verified with the results of experimental measurements performed in a bench scale RC1 Mettler-Toledo reaction calorimeter. The elaborated conclusions can be further employed in the parametric sensitivity analysis (Comput. Chem. Eng. 28 (2004) 527; Am. Inst. Chem. Eng. J. 45 (1999) 2429) to indicate a number of temperature sensors and their location inside the reactor, which will help to apply efficiently the divergence criterion method. (C) 2004 Elsevier Ltd. All rights reserved.