Archive for the ‘Double Skinned Tank’ Category

General information on Oil Storage Tanks

Wednesday, June 10th, 2009

Lets get the regulations and enforcement compliance’s out of the way first.

The facts:

Control of Pollution (Oil Storage) (England) Regulations 2001
Every year more than 5000 oil incidents are reported to the Environment Agency, that’s nearly 14 every day!.
Most incidents were caused by oil leaking from tanks either during storage or delivery. The Oil Storage Regulations will help us to stop these incidents by requiring tank owners to provide a secondary containment facility, such as a bund or drip tray to prevent oil escaping into the water environment.

Anyone storing oil in containers greater than 200 litres, above ground at an industrial, commercial or institutional site, or more than 3500 litres at a domestic site will be affected by these regulations. They cover factories, shops, offices, hotels, schools, churches, village halls, public sector buildings and hospitals.

•    Oil stores installed since 1st March 2001 must comply.
•    Existing oil stores “at significant risk” should have complied since 1st September 2003.
•    Existing oil stores must comply from 1st September 2005.

In general, an oil store is at “significant risk” if located within 10 metres of a watercourse or 50 metres of a well or borehole.

How are the regulations enforced?
The Environment Agency is responsible for enforcing these regulations throughout England. Should your oil storage facilities be inadequate, the Agency will provide advice and guidance to assist you with compliance. However, if you fail to act, the Agency may serve a notice requiring that the facilities be brought up to standard. Failure to comply with a notice is a criminal offence and may result in prosecution.

The regulations do not apply :

•    at premises used wholly or mainly as a single private dwelling storing less than 3500 litres. (but Building Regulations do apply for new and replacement domestic tanks);
•    at premises used for refining oil or its onward distribution;
•    any oil stored in a building or wholly underground;
•    to agricultural use of oil on farms – the storage of agricultural fuel oil is subject to the Control of Pollution (Silage, Slurry and Agricultural Fuel Oil) Regulations, 1991;
•    to waste mineral oil.

Requirements for storage of oil – general
Oil shall be stored in a container which is of sufficient strength and structural integrity to ensure that it is unlikely to burst or leak in its ordinary use.

The container must be situated within a secondary containment system which satisfies the following requirements – it must have a capacity of not less than 110% of the container’s storage capacity or, if there is more than one container within the system, of not less than 110% of the largest container’s storage capacity or 25% of their aggregate storage capacity, whichever is the greater; (b) it must be positioned, or other steps must be taken, so as to minimise any risk of damage by impact so far as is reasonably practicable; (c) its base and walls must be impermeable to water and oil; (d) its base and walls must not be penetrated by any valve, pipe or other opening which is used for draining the system; and (e) if any fill pipe, or draw off pipe, penetrates its base or any of its walls, the junction of the pipe with the base or walls must be adequately sealed to prevent oil escaping from the system.

Any valve, filter, sight gauge, vent pipe or other equipment ancillary to the container (other than a fill pipe or draw off pipe or, if the oil has a flashpoint of less than 32°C, a pump) must be situated within the secondary containment system.

Where a fill pipe is not within the secondary containment system, a drip tray must be used to catch any oil spilled when the container is being filled with oil.

Where any drum is used for the storage of oil in conjunction with a drip tray as the secondary containment system, it is sufficient if the tray has a capacity of not less than 25% of – (a) the drum’s storage capacity; or (b) if there is more than one drum used at the same time with the tray, the aggregate storage capacity of the drums.

Fixed tanks

Any fixed tank used for storing oil shall satisfy the following requirements:-

Any sight gauge must be properly supported and fitted with a valve which must be closed automatically when not in use.

Any fill pipe, draw off pipe or overflow pipe must be positioned, or other steps must be taken, so as to minimise any risk of damage by impact so far as is reasonably practicable and  (i) must have no mechanical joints, except at a place which is accessible for inspection by removing a hatch or cover; (ii) must be adequately protected from physical damage; (iii) must have adequate facilities for detecting any leaks; (iv) if fitted with a leakage detection device which is used continuously to monitor for leaks, the detection device must be maintained in working order and tested at appropriate intervals to ensure that it works properly; and (v) if not fitted with such a device, must be tested for leaks before it is first used and further tests for leaks must be performed, in the case of pipes which have mechanical joints, at least once in every 5 years and, in other cases, at least once in every 10 years; and (a) if above ground, must be properly supported; (b) if underground – be made of materials which are liable to corrosion, must be adequately protected against corrosion. The tank must be fitted with an automatic overfill prevention device if the filling operation is controlled from a place where it is not reasonably practicable to observe the tank and any vent pipe.

Any screw fitting or other fixed coupling which is fitted and is in good condition must be used when the tank is being filled with oil.

Where oil from the tank is delivered through a flexible pipe which is permanently attached to the container – (i) have a lockable valve where it leaves the container which is locked shut when not in use; and (ii) be kept within the secondary containment system when not in use. (a) The pipe must be fitted with a tap or valve at the delivery end which closes automatically when not in use; (b) the tap or valve must not be capable of being fixed in the open position unless the pipe is fitted with an automatic shut off device; (c) the pipe must be enclosed in a secure cabinet which is locked shut when not in use and is equipped with a drip tray or the pipe must

Any pump must be – (a) fitted with a non-return valve in its feed line; (b) positioned, or other steps must be taken, so as to minimise any risk of damage by impact so far as is reasonably practicable; and (c) protected from unauthorised use.

Any permanent vent pipe, tap or valve through which oil can be discharged from the tank to the open must satisfy the following requirements –

(a) it must be situated within the secondary containment system;
(b) it must be arranged so as to discharge the oil vertically downwards and be contained within the system; and
(c) in the case of a tap or valve, it must be fitted with a lock and locked shut when not in use.This applies to England but the same enforcement principles are applied elsewhere.

Bundled tank questions that I’ve often been asked?


There is confusion about the terms “double skinned”, “integrally bunded”, “twin walled” and “bunded” plastic and steel tanks in relation to above ground oil storage, and which are acceptable from an environmental protection point of view. Unfortunately manufacturers and suppliers of these tanks have used a variety of these terms with different interpretations.

Double Skinned Tanks

A Double Skinned Tank is just that – a primary tank with another “skin” placed around it with a very small gap (interstitial space) between the two; none of the pipework or ancillary equipment is contained. The risk of oil being lost from ancillary equipment and pipework is high; the Control of Pollution (Oil Storage) Regulations 2001 recognises this fact and require that tanks have all ancillary equipment such as sight tubes, taps and valves retained within a secondary containment system.
Double skinned tanks are not compliant with the Control of Pollution (Oil Storage) (England) Regulations 2001 unless additional secondary containment is provided for the tank and it’s ancillary equipment, such as an in-situ constructed bund (see Environment Agency/CIRIA Guidance notes on Masonry and Concrete bund construction).

Double Skinned Tanks are recommended for underground storage of oil/petrol etc because the interstitial space between the tank skins can be monitored for leaks. Underground installations should also have twin walled, non-corrosive pipework specified. See Pollution Prevention Guidance Note 27 – Installation, Decommissioning and Removal of Underground Storage Tanks, PPG7 – Refuelling Facilities (currently under revision) and the DEFRA Groundwater Protection Code: Petrol stations and other Fuel Dispensing facilities Involving Underground Storage Tanks.

Proprietary Tank Systems

Proprietary Tank Systems come in a large range of designs and are produced by many different manufacturers who may make certain claims about the environmental performance of their products. Proprietary Tank System or just Tank System is the preferred generic term for tanks often referred to as integrally bunded or twin walled, to prevent the confusion described above. Some tanks systems may have adequate secondary containment to comply with Oil Storage Regulation requirements, but some may be regarded as “high specification primary containers” and would therefore be non-compliant without additional containment.

To comply with the Control of Pollution (Oil Storage) (England) Regulations 2001, tank systems must have containment to minimise damage from third party interference, prevent pollution incidents from overfilling, leaking primary container or ancillary equipment. They should be sited to minimise the chance of damage by impact or collision or protected by suitable physical barriers.

If well designed, manufactured, sited, installed, used and maintained correctly a tank system can be just as effective as a conventional in-situ bunded tank.

The Environment Agency’s Pollution Prevention Guidance Note 2 – Above Ground Oil Storage Tanks gives some basic principles about the points to look out for when considering a tank system, products can be assessed against the check list.
If you have any queries about oil tanks and the Regulations in England or Wales please email


CIRIA (Construction Industry Research and Information Association) is a UK based association concerned with improving the performance of all involved in construction and the environment.
•    C I R I A /Environment Agency Joint Guidelines: Concrete Bunds for Oil Storage Tanks Guidance for the construction of simple, reinforced concrete bunds for oil storage tanks up to 3.5 metres wide and 900mm high. It is based upon CIRIA Report 163 “Construction of bunds for oil storage tanks”

DEFRA Oil Storage Regs DEFRA guidance note on the oil regulations

•    C I R I A /Environment Agency Joint Guidelines Masonry Bunds for Oil Storage Tanks. Guidance for the construction of simple, reinforced masonry bunds for oil storage tanks up to 3.5 metres wide and 1200mm high. It is based upon CIRIA Report 163 “Construction of bunds for oil storage tanks”
•    PPG02 Above ground oil storage tanks – Guidelines to assist those responsible for above ground oil storage tanks at sites other than oil refineries and distribution depots.
•    PPG26 Storage and Handling of Drums & Intermediate Bulk Containers – These notes are intended to assist all who deal with the storage and handling of drums and Intermediate Bulk Containers (IBCs).
•    Pollution Prevention Guidance Notes (PPGs)
Targeted at a particular business sector or activity PPGs provide advice to industry and the public on statutory responsibilities and good environmental practice.
•    Pollution incidents – an overview
In England and Wales, there were over 29,000 substantiated pollution incidents in 2003.