For many reasons, the storage of fuel Above ground is strictly controlled in Japan. Usually the volume of fuel will be restricted by the type of zoning and the surrounding buildings.
Above ground fuel limitations are usually referred in Liters of Type 3 fuel. The conversion of permitted volumes between Type 1, Type 2 and Type 3 is very simple. Type 2 is 50% of Type 3 and Type 1 is 50% of Type 2.
E.G. If you are allowed 10,000 L of Type 3 fuel, or you will be allowed 5,000 L of Type 2 fuel or 2,500 L of Type 1 fuel. A mix of fuel types if often seen. If you have Li-ion batteries, the electrolyte is treated at Type 2 fuel. You may also have Diesel in Day Tanks for your generators. Convert the Type 2 to Type 3 and then add the volume of Diesel. The total must be less than the maximum permitted Above ground volume.
Examples of Type 3 fuels would be Diesel, Marine (Bunker) oil and similar oils. Type 1 would be Petrol (gasoline), Benzine etc.
Planning to install Generators with Belly tanks will not work in Japan. All large fuel volumes must be in underground storage tanks only (UST). This is very different to other countries so be prepared to conform to the Codes in Japan if you want to get your building permit approved and the building certified for use. Don’t spend time asking for approval, this simply will not be given by the Fire Marshal.
USTs are very strictly controlled. A typical site would have between 10 to 18 inspections by the Fire Marshal during the delivery and installation of UST to the site. Your electrical contractor would be the best people to ask for details on USTs. There is so much, I could fill 10 pages with just UST requirements in Japan.
Each Fire Marshal’s area may have their own requirements which vary slightly from the overall fire Code. Such is life in Japan. Don’t fight the system, just go with the flow.
I have had Fire Marshals who insisted on including the volume of fuel in the supply pipes to the total Above ground fuel allowed. Others have simply not even asked how much fuel was in the pipes. It all depends on the area and how familiar the Fire Marshal is with Data Centres.