The thermal runaway behavior of an exothermic, heterogeneous, multiple reaction system has been studied in a cooled semi-batch reactor. The nitric acid oxidation of 2-octanol has been used to this end. During this reaction, 2-octanone is formed, which can be further oxidized to unwanted carboxylic acids. A dangerous situation may arise, when the transition of the reaction towards acids takes place accompanied by a temperature runaway. An experimental set-up was build, containing a 1-1 glass reactor, followed by a thermal characterization of the equipment. The operation conditions, e.g. dosing time and coolant temperature, to achieve a high yield under safe conditions are studied and discussed. The reaction conditions should rapidly lead to the maximum yield of intermediate product 2-octanone under safe conditions and stopped at the optimum reaction time. The appropriate moment in time to stop the reaction can be determined by model calculations. Also, operation conditions are found, which can be regarded as invariably safe. In that case, no runaway reaction will occur for any coolant temperature and the reactor temperature will always be maintained between well-known limits. The boundary diagram of Steensma and Westerterp [1990] for single reactions can be used to determine the dosing time and coolant temperature required for safe execution of the desired reaction. For suppression of the undesired reaction, it led to too optimistic coolant temperatures.