Secondary Containment Design & Construction

Key Design Considerations

Capacity & Size

The industry standards for bund capacity are the 110% and 25% rules. The 110% rule is applicable where there is only 1 container stored inside the bund, in this situation the calculation is simple, the bund needs to have a capacity of at least 110% of the primary containment volume. For example if a tank has a capacity of 10,000 litres, the bund needs to have a capacity of 11,000 litres.

For bunds storing multiple containers, the required capacity is the greater of either 110% of the largest container or 25% of the total volume stored.

The additional 10% capacity accounts for factors such as rainwater, firefighting media, and potential overfilling. It also helps mitigate the risk of overtopping caused by dynamic liquid movement during a spill, where the contents may surge or create wave effects within the bund.

Structural Dimensions

Once the minimum capacity is determined, the bund’s size and shape must be carefully designed. While a compact footprint is often preferred to minimize space usage on site, other critical factors must also be considered. The dimensions should account for hydraulic forces during catastrophic events - such as spigot flow, where a high-pressure leak can cause liquid to jet over the bund wall before hitting the floor, or the tidal wave effect, where a sudden large-volume release can result in overtopping. Proper design ensures the bund remains effective under these extreme conditions.

Wall Height

While bund wall height is primarily determined by volume requirements, practical considerations must also be taken into account. Taller walls can increase capacity, help contain spigot flow, and mitigate the tidal wave effect caused by sudden tank failure. However, excessively high walls may restrict access, reduce ventilation, and hinder firefighting efforts. To balance safety and functionality, bund walls should ideally not exceed 1.5 metres in height.

Construction Materials

Bunds can be constructed using reinforced concrete or reinforced masonry; however, specific sites may have unique material requirements that must be followed. Prefabricated bund wall systems - secured to an impermeable base - are a practical alternative, offering faster installation, lower costs, and the flexibility to be dismantled and reassembled if needed. For more details on the bund construction materials we offer, please see the Drop-downs below.

All bunds must be engineered to withstand the forces associated with a catastrophic tank failure - >potentially up to six times the normal hydrostatic pressure. Once construction is complete, a hydrostatic test must be carried out to confirm the bund is fully watertight before it is put into service.

Specialist Linings and Coatings

For a bund to be effective and compliant, its base and walls must be impermeable to the liquid it is designed to hold. Where a bund is not resistant to the material, the substance can attack the walls and floor, leading to structural damage to the bund. 

In order to make a bund impermeable we can apply specialist linings to the bund walls and floor, providing an effective seal and ensuring the bund is watertight. Various lining materials are available, but they should be designed to withstand attack from the material stored inside the bund.

Automatic Bund Dewatering

An effective bund will contain not only the intended liquid but also unwanted materials like rainwater and debris. Without proper maintenance, this buildup can reduce the bund’s effective capacity, potentially causing it to fall below regulatory requirements.

To address this, we offer automatic bund dewatering systems that remove clean water while retaining oil. These systems can detect oil levels as low as 5 parts per million, ensuring only clean water is discharged. They are especially valuable for remote or unmanned sites where manual maintenance is less practical.

Bund Wall Penetration

Penetrations into bund walls for pipework or cables should always be avoided. Where unavoidable, all penetrations for pipework or cabling must be effectively sealed to meet regulatory and site-specific standards.