The IEC 76 Norm for transformer design only includes basic measurements that do not cover mechanical design or protection of oil capacities against overpressure.
However, around the world, the design requirements of pressure vessels are strictly governed by the codes established by the American Society of Mechanical Engineers (ASME).
The blackout of IEC 76 Norm about mechanical design or protection of oil capacities against overpressure is very surprising. Obviously, transformer tanks are much more dangerous than most of the vessels subjected to ASME Norms, since they contain oil in contact with very high voltage cables.
Thus, during a transformer internal short circuit electrical arcs are provoking sharp gas generation, very fast over pressure, explosion and fire.
Because of the lack of verbiage of the IEC 76 Norm, many transformers only withstand to a very small overpressure and are not protected by Fast Depressurization Systems defined in the NFPA Recommendation 850.
Consequently, the market globalization has generated a disturbing fall of new transformer's quality, which clearly makes all power plants and substations more dangerous.