With the exception of vertical cone roof tanks hauling a roof slope less than two and one-half inches (2 1/2") in twelve inches (12") and in which the strength of the joint between the roof and shell, all aboveground tanks shall have some form of relief for preventing the development of excessive internal pressure in case of explosure fire surrounding the tank. The method of relief shall be acceptable to the clerk or his duly designated agent. (1961 Code)