Yacht & Boat Fuel Installations

The watertight nature of boats means that they also act as good containers for leaks or overflows of flammable liquids and vapours!

Stored fuels such as diesel or petrol in confined and undrained spaces carry the risk of providing fuel for a fire or explosion. All fuel system components must be in good condition. They must also be fire resistant, suitable for the fuel being used and kept away or shielded from sources of heat. To avoid pollution, spilt fuel oils are normally prevented from being discharged into the waterway. However, the overriding need to minimise the risk of fires, spread of fire and explosions, means that small amounts of overflowing fuel are better directed overboard than allowed to flow into the craft interior. These requirements and checks apply to all boats with inboard engines and to other fixed fuel systems supplying liquid-fuelled appliances such as diesel heaters.

Boats obliged to meet Boat Safety Scheme requirements must comply with the following:

  1. All permanently installed fuel systems and fixed engines must be designed, installed and maintained in a way that minimises the risks of explosion, or of fire starting or spreading.
  2. Fuel filling arrangements must prevent any overflow from entering the interior of the vessel.S Essential Guide
  3. All fuel filling points must clearly identify the fuel in use.
  4. Marking must be provided to identify the location of fuel system emergency shut-off devices, or their means of operation, which are not in open view.
  5. All permanently installed fuel systems must be designed, installed and maintained to ensure fuel-tight integrity.
  6. All permanently installed fuel tanks and fuel system connections must be accessible for inspection.
  7. The pressure systems of steam-powered installations must have a current inspection certificate issued by a recognised competent person.

An important preface on the nature of petrol

Petrol is very volatile, that is, it evaporates quickly generating highly flammable vapours. A small spill of petrol will create a large amount of vapour. Likewise, when it is being transferred and especially when a tank is being filled and the vapour in the ’empty’ tank is displaced by the liquid fuel. Even if the concentration of vapour is too rich to burn immediately, it will dilute to flammable or explosive levels, even though given enough ventilation, it may dissipate to a safe level eventually. Petrol vapour is three to four times heavier than air. It will sink to the lowest level of its surroundings, accumulating at low level in places such as unventilated lockers and bilges or in enclosed spaces such as the cabins and cockpits of boats.


As with petrol, diesel as a liquid does not burn, but when it is heated, the vapour given off is combustible and will burn strongly. To reach this stage, termed the flash point, diesel fuel only needs to be heated to around 56°Cand this can be lower in winter due to the anti-waxing additives.

Diesel can be raised to flash point temperature by contact with gas flames, frictional sparks, electric sparks, and small fires as well as other heat sources. Diesel fuel will ignite readily; materials soaked through with diesel and acting as a wick, greatly assist the spread of an established fire. Once alight, diesel burns with great heat and strength.
[based on information in the Library of Fire Safety, Vol. 2, Fire Protection Association,]

Extract from UK Boat safety scheme.