An essential part of the strategy for ensuring safe operating conditions for semi-batch reactors is the permanent guarantee of an admissible accumulation of reactants. Thus, even in case of a failure or a breakdown of the cooling system or the agitator, the maximum possible pressure and temperature in the reactor still remain within their permissible limits. The energy balance method makes it possible to monitor online the reactant concentration and to limit the accumulation by switching off the feed of reactant in time. Practical experience with a production plant is presented in which, over a period of 2 years, numerous process cycles were calculated and subjected to comparative analysis. The results show that the reproducibility as well as the accuracy of calculation are high and that the energy balance method can be regarded as reliable. In addition, recommendations for the implementation of this safety strategy as a reliable tool in plants are obtained. On this basis, the energy balance method provides additional information about the process and, thus, can provide an increase of plant safety and product quality by maintaining process availability.