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The ability of technical buildings to resist internal explosions produced by short circuits occurring in electrical transformers is an issue for the public authorities. Even if the probability of such an event is very low, the consequences can be significant and can easily put the surrounding public in danger due the blast, the projection of fragments and to the subsequent very toxic fire. The aim of this article is to investigate the consequences the blast on the structure of the technical building in which the transformer is located. The first part of this study deals with the estimation of the pressure load on the walls of the transformer's building. A complete modelling of the phenomenology is proposed starting from the electrical energy delivered into the arc, its transformation into gases, the efforts applied through the liquid onto the casing of the container, the expansion of the gases inside the building, the blast wave produced and its interaction on the inner walls of the building. In particular, the characteristics (amplitude and duration) of the shock waves are evaluated using the modelling tool 'DIFREX', developed by INERIS. This tool considers the evolution of the shock waves intensity, during their propagation and their reflection on obstacles (like walls). The overpressure signals and their time evolution are calculated according to an optimized spatial discretization in order to get the worst case for the structure. The second part describes the modelling of the building structure using SAP2000 software in order to evaluate its dynamic behaviour and estimate the internal forces induced by the explosion. The structural behaviour depends mainly on the characteristic duration of the overpressure and the overall stiffness of the building. The calculation is performed according a dynamic transient analysis. The results in terms of displacement and the effect on the reinforcement are given.