A new scenario for the calculation of the adiabatic temperature increase for semi-batch processes is presented. In the safety assessment of chemical reactions it is necessary to determine the Value of the Maximum Temperature attainable by runaway of the Synthesis Reaction for the worst case. We demonstrate that the batch scenario is not always the most dangerous way to carry out a reaction. In addition, an improvement in the calculation of the MTSR is presented in order to obtain more realistic scenarios.