Secondary containment is a critical aspect of effective spill prevention, dangerous goods compliance and environmental protection. A hazardous spill that escapes its secondary containment system is rarely “just a housekeeping issue”. It can rapidly escalate to a fire hazard, disrupt operations or becomes a reportable pollution incident.
Getting bund capacity right is one of the most robust ways to reduce the consequences of a loss of containment. A miscalculation can lead to severe consequences for people, assets, the environment and the business itself.
What is Bund Capacity (and why does it matter?)
A bund is a physical barrier designed to retain spills from tanks, drums, IBCs or process equipment. It is important to note that bund capacity refers to the usable volume available for containment, not simply the internal volume enclosed by the bund walls.
Why it matters:
Regulatory compliance: Failure to meet WHS obligations can expose organisations to enforcement action, including fines and regulatory notices
Workplace safety: Effective bunding can reduce slip hazards, minimise fire and explosion risks and limit worker exposure to hazardous chemicals
Environmental protection: Preventing spills from reaching stormwater systems, soil or waterways is a well-established focus of environmental regulation and enforcement across Australia. Regulators have the authority to impose significant fines and penalties for violations.
Operational continuity: Proper containment enables safer and faster spill response, reducing downtime and clean-up costs and preventing a localised leak from escalating into a much larger incident.
Knowing your Australian Standards
WHS law is performance-based and requires that an operator applies all practicable measures to reduce risks. Australian Standards represent recommended industry practices that should be applied where practicable. The following standards are commonly applied when assessing bunding and spill containment compliance:
AS 1940 – Flammable and combustible liquids (Class 3)
AS 4326 – Oxidising agents (Class 5.1)
AS 2714 – Organic Peroxides (Class 5.2)
AS/NZS 4452 – Toxic substances (Class 6.1)
AS 3780 – Corrosive substances (Class 8)
Common Pitfalls
While bund capacity approaches may appear similar across multiple standards and guidance documents, they are not always identical. As a result, misinterpretation or misapplication is common.
Common errors include:
Ignoring Displacement
Any equipment, plinths, pallets, pipework and other infrastructure within a bund occupy space, thereby reducing the effective available volume. These items should be accounted for when calculating effective capacity.
Overlooking Interconnected Tanks
Tanks that can drain together should be assessed as a single system. For example, if two 10,000 L tanks are piped together such that they could drain simultaneously, they must be treated as a 20,000 L unit for calculation purposes.
Defaulting to Simplified Rules
Applying a single “110% rule” or “25% rule” without checking the applicable standard or material class can lead to under-designed bunds.
Not Accounting for Jetting Effects
When a loss of containment occurs, released liquid may jet horizontally, creating a spray that can project over and beyond the bund wall, rather than simply pooling within the bund. Minimum separation distances must be provided between tanks and bund walls, relative to their height differences.
Getting it Right
At R4Risk, we recognise that effective bunding isn’t about ticking a box – it’s about understanding your site- specific risks and demonstrating that your containment strategy is conservative, defensible and properly maintained.
If you would like support reviewing your protection systems, assessing compliance or developing broader fire safety and risk studies, our team can help you navigate the detail with confidence.
