Bund Design Guidelines

One of the most critical aspects of spill prevention is the proper design and maintenance of bunds. Bunds are barriers designed to contain spills and prevent them from spreading. In the UK, widely used good-practice guidance is that secondary containment should be sized to hold at least 110% of the largest container’s volume (and, where multiple containers share the same containment, many guidance documents also reference the 110% / 25% approach). Bunds should be constructed from materials that are compatible with the substances stored, and regular maintenance is essential to ensure bunds are free from cracks, leaks and debris that could impede their function.

Key sizing and capacity principles

Base rule (single tank or container): design the bund (secondary containment) to hold at least 110% of the volume of the largest tank/container. Refer to: HSE secondary containment guidance, GOV.UK oil storage guidance.
Multiple containers within one bund: many UK guidance sources reference designing to hold the greater of 110% of the largest container or 25% of the total stored volume, subject to risk assessment and site specifics. Refer to: NetRegs secondary containment systems (bunding).
Usable capacity matters: ensure the calculated volume is the effective capacity, allowing for: tank supports, pipework, pumps, internal structures, and any displacement within the bund footprint.
Rainwater allowance (where outdoor): consider how rainfall will be managed so capacity is not compromised during normal operation (see “Drainage and water management” below).

Materials and compatibility

Use materials that are impermeable and chemically compatible with the stored liquids (oils, fuels, coolants, acids, alkalis and other chemicals may each require different design choices).
For proprietary containment (e.g., bunded pallets, IBC sumps), select products designed for chemical resistance and load rating appropriate to the containers stored.
For constructed bunds, ensure the floor and walls provide a continuous barrier (including joints, penetrations and interfaces with walls/columns).

Construction essentials

Provide a continuous, sealed base and upstands/walls to prevent seepage.
Minimise penetrations; where unavoidable (e.g., pipe entries), use suitable seals and detailing to maintain integrity.
Protect against impact damage from plant, pallets, drums and IBC movements (consider barriers, kerbs or designated handling routes).
Ensure safe access for inspection and spill response (clear walkways, adequate lighting, and space for equipment).

Drainage and water management

Avoid uncontrolled drains from bunds. Any drainage arrangement should prevent pollution and ensure the bund remains effective.
Outdoor containment should prevent rainwater filling the bund. Practical options include: covered storage, canopies, or containment products designed for outdoor use.
If a bund has a sump or drain point for rainwater, it should be managed with a controlled procedure (only discharge when verified clean), and in line with site environmental controls.

Inspection and maintenance

Inspect bunds routinely for cracks, damage, degraded sealants, staining, and evidence of leakage.
Keep bunds clear of debris and stored items that reduce capacity or obstruct response.
Remove accumulated liquids promptly (following site procedures) so the bund is ready to contain a spill.
Record inspections and repairs. A simple log supports consistent compliance and helps identify recurring issues.

Choosing the right containment type

The best solution depends on what you store (drums, IBCs, tanks), where you store it (indoors/outdoors), and the liquids involved. These Serpro pages may help when selecting practical containment:

Drum and small container containment: Bunded Drum Trays
IBC storage containment: IBC Containment
Portable containment for temporary works and maintenance tasks: InstaBund Portable Bunding
Weather-protected outdoor storage options: Covered Bunds & Pallets - Storage
Spill response equipment to support bunding and containment on site: Spill Kits
Preventing spilled liquids reaching drains: Drain Protection
Overhead leak control (to limit how much reaches the bunded area): Leak Diverter

Recognised UK guidance and references

HSE (COMAH) secondary containment overview: Secondary containment
GOV.UK guidance on storing oil (includes secondary containment expectations): Storing oil at a home or business
NetRegs guidance on bunding and capacity rules: Secondary containment systems (bunding)
Pollution prevention guidance for drums and IBCs (PPG 26): PPG 26 PDF
CIRIA containment good practice (C736) overview: Containment systems for the prevention of pollution (C736)

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