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Bunded fuel storage tanks are used to store hazardous substances - domestic heating oil. They contrast from other oil storage tanks, for example, 'single skin tanks' since they have an extra tank or 'outside skin' (otherwise called bunding). This means if any oil spills from the principle storage tank, the fuel will be securely contained inside the outside layer, or boundary, preventing external spillage.

As this solid, protective layer makes the tank safer and stronger, it is likewise more costly than a 'single skin' tank that stores a similar measure of fuel. You are effectively getting two tanks.

Extra benefits of a bunded tank?

Beside having a 'second skin' to counteract oil spills, bunded tanks have a few extra benefits as standard, and these differ depending upon the make, model and size.

  • A tank guage evaluate how much fuel is left in the tank and whether a refuel is required.
  • A lockable fill point to help discourage fuel theft.
  • A secure fuel inspection hatch designed to access the fuel and clean the tank.
  • An alert system to warn of any sudden drop in fuel (either due to leakage or oil theft).
  • An overfill protection device to prevent putting too much oil in the tank.

How much fuel can the bunding hold?

In case of an oil leak, the external area is designed to hold more than the limit of the inner tank. The measure of fuel this extra layer can contain relies upon the make and model of the tank, however the minimum is 110% of the fuel limit of the inner tank.

Further advantages

Bunded fuel storage tanks are considered the environmentally-friendly choice, as their strong, protective layer keeps any harm to the surrounding territory. The dual layering likewise helps prevent fuel theft, as the additional layer makes it harder to take fuel from the inner section of the tank. The outer layer also helps protect the inner layer for impact damage.



What types of oil storage tanks are available?

There are three generic types of oil storage tanks:

  • single skin (which may be installed in a reinforced concrete or masonry bund)
  • double skin (predominantly commercial underground applications (USTs))
  • integrally bunded (above ground and within buildings)

Oil storage tanks are made of steel or polyethylene and can be supplied in a range of shapes and sizes to suit the site requirements.

Will my storage tank require any servicing or regular maintenance?

During a service visit, the oil engineer should check your oil storage tanks and oil supply pipes. The service engineer should inspect the tank for water contamination, clean or replace the oil filter and visually check accessible fittings for oil leaks.

If you have a steel tank, you may need to paint it to prevent corrosion.

What is a bund?

A bund (or catchpit) is a secondary containment system designed to prevent fuel lost from the tank escaping into the environment. Bunds may be constructed from masonry or concrete to contain a single-skin oil storage tank and must be able to hold at least 110% of the tank’s contents should a leak or overspill occur. Integrally bunded oil storage tank systems are available and are a practical solution.

Does a domestic oil storage tank require secondary containment (bunding)?

Under building regulations for England and Wales, if the oil storage tank’s capacity is:

  • Over 2500 litres – it must have secondary containment (bunding)
  • Up to 2500 litres – it may need bunding depending on the outcome of an individual site pollution risk assessment. A single skin tank would only be allowed where there is no risk of oil reaching for example, a watercourse, water extraction point or aquifer after a release of oil from the tank.

Your local OFTEC-registered tank installer will be able to make a fire and pollution risk assessment and advise on the type of tank most suitable for an installation.

What is “controlled water”?

Controlled waters are rivers, streams, lakes, canals, coastal waters, estuaries and groundwater. It refers to all water which is below the surface of the ground in the saturation zone and in direct contact with the ground or subsoil.

An oil tank pollution risk assessment should also consider any ditches, soakaways, septic tanks and gullies which could pollute groundwater or reach controlled waters. Environment Agency defined Special Protection Zones (water abstraction points and aquifers) should be equally protected from oil leakage.

What fire separation distances apply to domestic oil storage tanks?

What fire separation distance is required from an oil storage tank to LPG cylinders?

Can I disguise my storage tank with a screen?

Yes, screening of domestic oil storage tanks is permitted. You should allow enough space for service access for inspection of the tank and filter maintenance, etc. British Standards require a minimum of 600 mm separation between a tank and screening. If the screening forms part of the property boundary, the separation should be 760 mm unless a fire barrier is erected.

Can I install an oil storage tank inside?

Yes. Under British Standards a domestic oil storage tank up to 3500 litres capacity may be installed within a building so long as the tank has secondary containment, such as an integrally bunded oil storage tank, the tank is contained within a one-hour fire-resistant chamber and is located at the lowest possible level. The chamber should contain nothing but the tank and be ventilated to the outside.

Can I install an oil storage tank underground?

If an underground oil storage tank is to be directly buried below ground it should be specifically constructed for underground use and should be installed strictly to the manufacturer’s instructions. The recommendations in the Environment Agency’s Pollution Prevention Guidance note PPG 27 should be followed and planning permission may also be required.

If an oil storage tank is removed from its base temporarily, for example to repair the base and piers, would I be allowed to reinstall the original oil storage tank as it was before or would I have to treat this as a new installation?

You can reinstall the original tank, but OFTEC recommends that all oil storage tank installations comply with regulatory requirements and industry guidance. The installation of a ‘new’ or ‘replacement’ oil storage tank would fall within the scope of current building regulations.

Why is the support given by the oil storage tank base so important?

It is important to give domestic oil storage tanks, whether of steel or plastic, stable bases and supports. This makes them safe and will protect the environment.

If an oil storage tank is inadequately supported the oil storage tank itself can be weakened leading to the eventual failure of the oil storage tank and escape of the stored fuel. During the life of an installation, an oil storage tank base will need to provide continual structural support even though ground conditions may alter from season to season and year to year.

What should the oil storage tank base be made of and what dimensions does it need to be?

To comply with British Standards, the base material should be one of the following laid on a hardcore base to give an imperforate base:

  • concrete at least 100mm thick
  • paving stones at least 50mm thick
  • stonework at least 50mm thick

The overall size of the base should be larger than the oil storage tank and any integral oil storage tank bund, so that when the oil storage tank is installed, the base has a clear projection of a minimum of 300mm around all sides of the oil storage tank.

Why is the tank base required to extend 300mm around the perimeter of the oil storage tank?

The fire protection provided by the base is to help prevent the tank itself from becoming overgrown and to help protect against fire spreading across the ground to the contained fuel from another source. If the tank is raised on piers, the platform supporting the tank should be sized to sufficiently support the tank. Reference should be made to the tank manufacturer’s installation instructions.

What is the remote fill pipe for?

Remote fill pipes are provided for oil storage tanks sited more than 30m from a road, or where there is restricted access generally. For domestic installations this is usually a 50mm steel pipe connected to the tank and routed to an accessible position. The pipe should incorporate a screw cap at the fill point, a gate valve, a non-return valve and be adequately supported.

Due to increased risk of spillage during filling, the tank it serves should have secondary containment, such as an integrally bunded oil storage tank, and should be fitted with a device to stop it being overfilled. An audible overfill alarm is also recommended.

My oil supplier has refused to deliver oil to my underground oil storage tank until I have a report in place confirming that my tank is in reasonable condition to safely store oil. Can an OFTEC Registered Technician provide this report?

Most OFTEC registered technicians are unlikely to be able to offer this service. Underground oil storage tanks should only be assessed by persons who have specialist knowledge and possess appropriate equipment to conduct such work. Contact OFTEC’s technical helpline for assistance in locating a suitable specialist. Call 01473 626 298 or enquiries@oftec.org.

What can I do to protect my oil tank from theft?

1) Check the fuel levels regularly to make sure that none has gone missing.

2) Lock the tank. Most tanks can be locked at the inspection cover or a lockable filler cap can be retro fitted to existing oil tanks.

3) Install automatic movement sensor security lighting around the tank.

4) Consider having an alarm system fitted to the tank which will warn if oil levels drop suddenly. This could also be useful if an oil leak occurs.

5) Be vigilant following a delivery – some fuel distributors have reported that their delivery vehicles have been followed in the past. Thieves may also return to steal replacement oil following an initial theft.

6) Plant shrubs or use fence panels to hide the tank from the road, but make sure any screening should be a minimum distance away from the tank so it doesn’t cause a fire hazard or prevent access for deliveries and maintenance.

7) Make sure your tank is clearly visible from your home.

8) If your property has gates, keep them locked at night and when you are not at home.

9) Report any suspicious activity to the police.

10) Join a neighbourhood watch scheme or make arrangements with your neighbours to keep a watch out - the more eyes the better!

11) Check that your home contents insurance covers oil theft.