How big does my secondary containment for a single oil container need to be?
For one tank, mobile bowser or Intermediate Bulk Container (IBC), the secondary containment must be able to hold 110 per cent of the volume that the container can hold. For one storage drum you can store it on a drip tray.
The drip tray must be able to hold 25 per cent of the drum's total volume – not 25 per cent of the amount of oil the drum has in it.
How big does my secondary containment need to be if I have more than one container in a storage area?
More than one tank in the same secondary containment system
If the tanks aren’t hydraulically linked but are in the same secondary containment system, the containment capacity must be a minimum of 25 per cent of the total capacity or 110 per cent of the largest tank, whichever is greatest.
If the tanks are hydraulically linked but situated in the same containment system, they should be treated as one tank. The containment capacity should be a minimum of 110 per cent of the total capacity of the tanks.
Tanks in different secondary containment systems
If the tanks are hydraulically linked, but in separate containment systems, containment of at least 110 per cent of the total volume stored is required at each location.
There may be benefits in hydraulically linking the secondary containment systems.
Storage of multiple oil drums
If you are storing more than one drum on a drip tray the drip tray must be able to hold 25 per cent of the total volume for the number of drums that can be stored on it.
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.
Where can I find information on building a bund?
The Construction Industry Research and Information Association (CIRIA) report 163, on the construction of bunds for oil storage tanks, explains how to build good quality bunds.
You need to make sure your bund is built properly. It must be able to withstand total failure of a full tank.
What is an acceptable impermeability level for a constructed bund?
The regulations state that a container's base and walls are both 'impermeable to water and oil'. The regulations don't specify any particular construction materials for a secondary container.
A conventional bund constructed from bricks and mortar is unlikely to be impermeable without rendering or coating to achieve a permeability coefficient of not less than 10-9 metres per second.
Can I take the volume of the primary tank into account when calculating secondary containment capacity?
Yes, the regulations don't specify otherwise. They simply state that the secondary container 'must have a capacity of not less 110 per cent of the container’s storage capacity'.
The primary container volume can be taken into account where applicable.
Most proprietary tank systems are designed so that the oil finds its own level in both containers if the primary container leaks. In this instance, the primary container contributes to the total containment capacity. You should take into account that these systems may only provide a 10 per cent containment capacity in the event of overfilling.
Oil will also find its own level in a conventional bund when the tank is situated low down.
For example, a maximum volume delivery made to a tank more than 10 per cent full will result in a loss of oil from the secondary containment.
The use of an overfill prevention device is good practice and you should consider these or other additional pollution prevention safeguards, such as additional containment capacity in sensitive locations.
Other secondary containment options
An oil separator isn’t a form of secondary containment. We consider this to be tertiary containment and will not be accepted as containment under the OSR England.
