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The answer to this question is a bit more complicated than just two numbers. It depends on a number of factors, but especially the rating of the tank, the location of the tank and pump (i.e. above ground, outdoors, indoors, etc.), the wall rating for the tank and pump room (where applicable), and the physical capacity of the tank (i.e. +/- 6000 gallons). I suggest you review NFPA 20 and 37 plus UL 142 and the IFC where applicable. And please note that NFPA 30 doesn't apply here since the tank is part of the fuel system for an internal combustion engine.
Cheers.