In the event of a large hydrocarbon fire in a fuel storage site, atmospheric tanks are exposed to a heat flux of long duration. Accidents experienced in the past (Port Edouard Herriot, Buncefield) shows that large bund fires can last several days. Under these circumstances, even slightly volatile fuel may reach the distillation onset temperature, typically 180°C for diesel. If venting is not adequate, vapour generated by the distillation process produces a pressure build-up which is dangerous for tank integrity. Atmospheric cylindrical vertical tanks and more precisely the bottom/shell welding are indeed very sensitive to vapour pressure. An effective vapour pressure exceeding 10 kPa(g) may thus cause a catastrophic rupture of the tank bottom which is highly dangerous for the fire fighting personnel.
