The requirements for installation of a fuel system on a boat with fixed fuel tanks are given in the harmonised standard BS EN ISO 10088 Permanently installed fuel systems and BS EN ISO 21487:2012 Small craft - Permanently installed petrol and diesel fuel tanks.
The requirement for petrol fuel tanks to be ‘insulated from the engine and all other sources of ignition’ is deemed to be complied with if
a) the clearance between the petrol tank and the engine is greater than 100 mm and
b) all electrical parts on the engine which could create a spark, and any other electrical components in the engine/fuel compartment, are ignition protected. To ensure that these components are ignition protected the boat builder should use a petrol engine that complies with BS EN ISO 15584 Inboard petrol engines - fuel and electrical system components (the engine manufacture should provide this confirmation) and for other parts, e.g. blower fan or electric bilge pump, use only components that have been CE marked in accordance with Annex II 1. The clearance between a petrol tank and any dry exhaust components must be greater than 250 mm, unless an equivalent thermal barrier is provided. For diesel engine installations, the engines used should comply with BS EN ISO 16147
Inboard diesel engines – Engine-mounted fuel and electrical components to ensure that the fuel components fitted on the engine by the engine manufacturer are safe. The engine manufacture should provide confirmation that the engine complies with this standard.
Fuel hose used in the system must be fire resistant if used in the engine compartment and Where fuel hose is used the standard requires that only fire-resistant hose to BS EN ISO 7840 may be used in the engine compartment. Such hose should be stamped to indicate compliance
This appears to be a requirement in BS EN ISO 21487:2012
If there is a drain in a diesel oil tank, it shall be fitted with a shut-off valve having a plug that can be removed only with tools.
Each tank shall have an inspection hatch of at least 150 mm diameter. The inspection hatch shall, as a rule, be located on top of the tank, but for diesel oil tanks it may also be on the tank side. There shall be access to the inspection hatch when the tank is in position.