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What is a bunded oil tank?

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When you start thinking about replacing your oil tank and doing some research into what is permitted under the current regulations and what is not, one of the first words, which is quite likely to be a new one to you is “bunded”. This essentially means that the oil tank is surrounded by a second skin of plastic. In an agricultural setting, bunds are generally used to protect and help collect run off and the principle is very similar.

When your oil tank becomes old starts to reach the end of its life, as all things do, there is a risk that if the tank is filled, the additional pressure and weight in it can cause any cracks or areas of vulnerability to be put under too much strain and the tank will start to leak. If you have an elderly steel tank, this will generally be more subtle, and you will see some seeping along the weld or perhaps some dampness from corroded patches on the bottom. If you have missed these early warnings or if you have a single skinned plastic tank, the failure of the tank can be much more dramatic and, in some instances, catastrophic.

The idea of a bunded oil tank is that when the times comes for the original tank to fail, the outer skin will keep the contents safe and will give you a small window of opportunity to replace the tank by making informed decisions rather than rushing at it with a knee jerk reaction, which you will then have to live for, for the next 20-years or so.

Bunded Oil Tank Capacity

A bunded tank must hold 110% of the primary tank’s capacity, so if you have just had it filled – and this is very often the time when a tank fails, the contents will still be kept securely inside the outer bund. You will find that the inner and the outer tank levels will equalize and be around the same and this is a good indicator that the inner tank has actually gone rather than the fuel company delivering into the bund by mistake. If this happens, the bund may be filled right up but the inner tank still waiting to receive the fuel that you have ordered!

Some bunded tanks are sold with the option of having a bund monitor fitted and, especially for the larger tanks, this is a very useful tool. Typically, it will be battery operated and so when the delivery driver comes to fill the tank, it is best practice just to check this before he starts to put fuel in it. Similarly, as a tank check is part of the boiler service, your boiler engineer should press the button to check that nothing has happened since the last fill and he will be able to tell you if there is oil present in the bund and also confirm that the battery is not flat. You will also be able to check this yourself from time to time for peace of mind that all is well with your bunded oil tank.

Generally, most domestic tanks and all commercial tanks need to be bunded these days. One of the key things is that when your tank does get to the stage when it needs replacing, any leakage or even overfill must avoid getting in the drains at all costs, as the Environment Agency can and will levy large fines for oil contamination and clean-up costs can be huge. When the OFTEC engineer comes to give you a quotation for the replacement of your tank, he may use a form called a CD10, which looks at the positioning of the new tank and takes into consideration the proximity to drains, manhole covers, ditches and wells, as well as other obstacles which could mean that there is no way that a single skinned tank could be legally installed. Generally, he will need to justify why he is installing one as opposed to a bunded tank and put his name to it. As you can imagine, this means that single skinned tanks are now rarely installed.

In an attempt to encourage the use of bunded tanks, plus the additional safety that they provide, the tank manufacturers provide a 10-year warranty with bunded tanks as opposed to the general 2-year warranty with single skinned tanks. Even though bunded tanks are more expensive to buy at the outset, another advantage is that the tank has an additional eight years of guarantee, should you need it.

Thursday 29th July 2021
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