Double Skin Tanks vs. Open Bunded Tanks

Double Skin Tanks vs. Open Bunded Tanks


Our open bunded tanks come with 110% bunding for multi-use products and include:

  • Complete shutdown of tank via two 6" 1/4 gate valves on the product inlet and outlet valve in the bund area, complete with extension handle allowing easy operation without having to enter the bund.
  • Open bunds can be easily cleaned if overfilled.
  • No danger of cross contamination of different products; tank and bund area can be visually checked and easily cleaned.
  • Primary tank can be removed from bund for maintenance, tank survey and cleaning.


A twin wall / double skin tank is not classed as a bunded tank unless it has 110% overfill capacity.

If the double skinned tank is 110% bunded and used in a hire fleet as a multi-use tank, there are potential issues that as a hirer you should be aware of.

  • With a double skinned tank, it's extremely difficult to clean if the void area of the tank is overfilled.
  • It's extremely difficult to visually check the void area for maintenance with double skinned tanks.
  • With double skinned tanks, issues can arise with potentially dangerous effects if overfilled with two different and incompatible products. This is very important and you should check with your supplier the history of materials previously stored in your hire tank.

Based on the above, this is the reason that we only use double skin tanks as single product containers, i.e. diesel.

Be compliant with UK regulations

A twin wall or double wall tank that does not have 110% overfill capacity is classed as a "High specification PRIMARY container", it is not a bunded tank and may not be compliant.

"CIRIA Report 163 defines secondary containment as a containment system that is capable of preventing the escape of material (oil) to aquatic environment in the event of failure of the primary storage container. It should be noted that a double skinned primary container will not, in itself, provide secondary containment." *

If a tank is the primary container, then it should go into a bunded area. If it is not in a bunded area, then it does not comply when secondary containment is required.

Bunded Tanks

If you would like to know more information about our bunded tanks, or would like to hire a bunded storage tank, please contact our hire tank advisers on 01502 710100.

* CIRCA Report 163