In the assessment of hazards linked to chemical reactions, two aspects must be considered : the behavior of the reactor under normal operating conditions, i.e. the controllability of the reaction rate and the behavior in case of failure. The maximum temperature which can be attained in the case of a cooling failure by an exothermic synthesis reaction (MTSR) is a parameter of great significance for the assessment of the thermal safety of semi-batch reactions. This temperature depends on the accumulation of non-converted reactants at the instant of the failure. In most cases, the determination of MTSR is possible after one experiment performed in a reaction calorimeter following standard operating procedures. Such an experiment allows the evaluation of the heat of accumulation as a function of time during addition of reactants. However in some cases, with multiple reactions, another experimental approach, including simulation of the failure and coupling of spectroscopic methods, has to be used. Examples will illustrate the determination of the MTSR in such more difficult cases.