The provisions of this section of Part 2 in the 2002 BSS Standards are mandatory for non-private boats where applicable.
No piping system is immune from the risk of fracture and in the event of this happening it's essential to provide a way to minimise the risk of losing all of the tank's contents (see also fuel pipe & hose connections, fuel filters and fuel cocks & valves). For this reason fuel supply lines in petrol systems must be taken through the top of the tank, with the only exception being for purely gravity-feed systems found on older boats. In these cases the fuel feed will be at the bottom of the tank and there must be a shut-off valve or cock fitted at the tank connection.
Again, it's a good idea if your boat is powered by diesel to ensure the fuel feed or return pipes are drawn through the top of the tank, or as near to the top of the tank as is practical.
Any diesel-fuelled boats built to comply with ISO BS EN 10088 should already have fuel feed pipes entering through the top of the tank or at the top of the side of the tank. If feed or return pipes are fitted below this level, they will be protected by a valve or cock attached to the tank, unless the pipe is welded to the tank and reaches above it. [2.12]