There is often a lot of confusion around secondary containment. Secondary containment is a second line of defence used to avoid, monitor, or mitigate major hazardous incidents. The big question is however, does your liquid storage comply with regulations?
Below we will cover the basic information on secondary containment requirements to ensure you are audit ready and compliant.


What is a bund?

A bund is a secondary containment system that is used to catch leaks or spills from a main containment system, such as a storage tank. Any liquid that escapes the primary containment is held in the bund and prevented from overflowing onto the site or escaping to the atmosphere. A bund is made up of an impermeable floor and a collection of impermeable walls for a watertight area around a storage tank.


Do I need a bund?

In short, the answer is yes.
All hazardous liquid storage should have secondary containment because an uncontrolled spill could be catastrophic and cause environmental damage, creating a dangerous working atmosphere. Not only that, but you can face prosecution, unlimited fines and will be responsible for all clean-up costs under the polluter pays concept.
There are some questions you need to ask yourself:

  1. What kind of liquid is being stored? What are the ramifications for the environment? If you are storing liquids near bodies of water, for example, bunding is a must.
  2. How long will the liquids be stored for? Liquid storage containers can fail at any time, and the probability of failure increases as the container gets older.
  3. What is the approximate volume of liquid? Bunds can help avoid catastrophic containers spills, saving time and money in the clean-up process.
  4. Is your business ready to deal with the worst-case scenario? Spill kits, when used in conjunction with proper bunding, may provide peace of mind, as well EPA compliance.


There are also many regulatory controls to be aware of including.

  • Control of Pollution (Oil Storage) (England) Regulations 2001
  • Control of Pollution Act 1991
  • COMAH Regulations 1999
  • Control of Substance Hazardous to Health Regulations 2002
  • Dangerous Substances and Explosive Atmosphere Regulations


Bund Specifications

The industry standards are the 110% and 25% rules.

When only one container is contained within the bund, the 110% rule applies; in this case the equation is simple: the bund must have a capacity of at least 110% of the primary containment volume. For example, if a tank has a 10,000-litre capacity, the bund must have an 11,000-litre capacity.


The equation is slightly more complex for bunds that house several containers; the bund must be able to accommodate either 110% of the largest primary containment or 25% of the total volume of the primary containers, whichever is greater.

Extra liquids, such as rainwater, firefighting media, and overfilling of the tanks, can be accommodated by the extra 10% space. It also reduced the risk of liquid overflowing the sides of bunds when the stored liquids are a dynamic load, which means the liquid within the bund is not static, creating a wave effect.

Bund Maintenance

Bunds that are not adequately maintained may develop failures which prevent them from functioning properly. Bund maintenance is an incredibly important aspect that is often ignored, as all infrastructure wears out over time and can become unfit for use if not properly maintained. Maintaining a proper maintenance and inspection schedule will help prolong the life of your bunds by allowing any required repairs to be completed in a timely manner, preventing the damage from worsening.

Regular inspections
Bunds must be inspected on a regular basis to ensure their integrity, imperviousness to liquid contents, and effectiveness as a part of the PIRP.

  • Rainwater Removal - Bunds that work well can collect and store everything that comes within them, including not just the liquid they are meant to catch, but also unnecessary material like rainwater. If a bund is not properly managed, unwanted build-up will reduce its capacity and cause it to fall short of the capacity requirements.
  • Bund Surveys - Periodic inspections of the bund walls, floor, any penetration seals, and bund linings should be carried out in addition to routine rainwater removal. If any faults are discovered, they should be corrected as soon as possible to prevent the problems from worsening. Even hairline fractures can allow liquids to escape the bund, and structural flaws can greatly undermine the bund walls, potentially leading to failure in the event of a volatile load.

How often does this happen?
Onsite managers should inspect their bunds monthly. Additionally, professional inspections should be carried out at least every 2 years. Hyde Park Environmental offer this service, see our website along with our products on:


Bund Repair

A broken bund is just a bad as no bund. It is essential to get them fixed as soon as possible because it can mask leaks and give a false sense of security. Chemicals/ oil leaching from bunds can go unnoticed for a long time, contaminating the ground and groundwater.
Bunds with cracks must be repaired to ensure that they are not only watertight but also have the structural integrity to withstand a catastrophic failure. The bund will need to be relined or patched if the lining has failed.
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