Rank: Super forum user 
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Not my area of expertise so I would be grateful for some advice. We are installing a standby generator with a 7000 litre double skinned storage tank. The contractor is proposing a drip tray under the genny but submits that the double skinned tank suffices and therefore a bund is not required. My understanding of the Oil Storage Regs and the Environment Agencies guidance PPG2 seems to indicate the opposite & that a 110% bund is still required. Any assistance gratefully received.
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Rank: Forum user
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As I understood it, it is a double skinned tank or a 110% bund, I havent seen any specifc requirements to have both. In my last company the EA visited us regularly and we had double skinned tanks with no bunds they didnt raise any issues there so...
From a risk assessment point of view the double skinned tank is more than enough, the chances of both layers being breached is extremely low.
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Rank: Super forum user
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You should find your answer in the DEFRA document 'Guidance Note for The Control of Pollution (Oil Storage) (England) Regulations 2001'. Information is also available in the Environment Agency publication PPG2 of April 2010. Both are on the www. The latter document suggests that you will probably need a secondary containment system or bund even if you have a double skinned storage tank. Hope this helps.
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Rank: Super forum user
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In my opinion needs to be bunded.
Consider the filling arrangements. Are inlet valves/connections within the double skin? Not ususally so thus if there were to be a failure of connection during filling oil/fuel could end up falling to ground.
consider material of construction - plastic? Usually so - is their sufficient protection against physical puncturing e.g. from vehicle impact? Whilst an "armco" type barrier would reduce the risk of physical damage a bund does that and guards aginst other possible scenarios.
If contents should escape and Env Agency has to carry out clean up they are likely to seek to recover their costs. That is not covered by 99.9% of liability policies! Might be worth checking the EA stats about most common cause of water pollution.
My advice is do a risk assessment - I am sure that you will come to conclusion that bund is necessary. Anyway I consider it to be a legal requirement - and you might like to seek view of your insurer.
Phil
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Rank: Super forum user
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(Copy and pasted from link below)
How do I know if my double-skinned tank complies with the regulations?
A double-skinned tank, otherwise known as a twin-walled tank, is unlikely to provide adequate secondary containment on its own.
Double-skinned tanks have an inner tank surrounded by an outer skin for extra strength. Don’t confuse double-skinned tanks with integrally- bunded tanks; they don’t give the same protection against oil loss from overfilling, or damage to tank and pipework damage, and require extra secondary containment when installed above ground.
Effective secondary containment will include ancillary equipment as well as the storage tank. This means that sight gauges and valves should also be inside the secondary containment facility. Vent pipes should discharge vertically in the secondary containment facility
http://www.environment-a...ss/topics/oil/32008.aspx
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Rank: Moderator 
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Rank: Super forum user
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Interesting comments. I too thought that if a tank was double skinned it did not need bunding. Then I had a look inside a contractor's tank and saw that the space between the two skins had a significant amount of fuel in it and that at this rate if the outer tank was damaged we would a significant environmental incident. So I think a bund is in order but a do a risk assessment first- it might be that the double skin will provide protection as long as there is a seal around the inlet preventing fuel getting between the two skins.
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Rank: Super forum user
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The absolute guide is the 100% requirement for containment and most double skinned tanks do NOT meet this. The double skin is about reducing the risk of puncture but in practice most impacts do cause breach of both skins. Proper bunds also require suitable impact protection as well as containment of all valves, hoses and nozzles.
Bob
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