How to Calculate Bund Capacity To Meet Australian Standards

Date Posted:5 September 2025

Learn how to calculate bund capacity correctly under Australian Standards. Protect workers, avoid costly fines, and ensure environmental compliance with simple, clear steps.

Why Bund Capacity Matters

Bunding is a safety measure used to contain hazardous liquids in case of spills or leaks. It involves a barrier or containment area (known as a bund) that surrounds tanks, drums or IBCs to capture any escaping fluid.

While often overlooked, correct bund capacity is vital for:

Workplace safety – Prevents slip hazards, fire risks, and chemical exposure
Environmental protection – Stops pollutants from reaching drains or soil
Legal compliance – Fulfils obligations under WHS and EPA regulations

In Australia, the commonly referenced AS 1940-2004 standard and the 110% Rule are often misunderstood. Many workplaces miscalculate bund volume, risking non-compliance and heavy penalties.

blue verdex 2 drum bunded spill pallet with steel cylinder drums

What Is Bund Capacity?

Bund capacity refers to the maximum volume of liquid a bund can safely contain during a spill. This isn’t just the total internal volume of the bund, but a compliance-driven figure based on:

The size and number of containers within the bund
The type of liquid stored
Displacement caused by the tanks themselves

Put simply, bund capacity must ensure enough room remains available to fully capture a spill, even when containers occupy part of the bund’s volume.

How to Calculate the Correct Bund Capacity

To meet compliance requirements (especially under AS 1940), you must calculate bund capacity using the most conservative volume from the following scenarios:

1. 110% of the largest single tank

This is the most commonly applied rule.

Example:

A tank holds 1,000L
The bund must hold at least 1,100 litres (1,000L x 110%)

This ensures that a complete spill from the biggest tank doesn’t overflow the bund.

For drum storage, using drum trolleys and lifters with bunded pallets ensures safer handling and compliance with these rules.

2. 110% of interconnected tanks

If two or more tanks are connected and could all leak at once, you must treat them as a single unit.

Example:

Three linked tanks: 600L + 500L + 400L = 1,500L
Bund must hold 1,650 litres (1,500L x 110%)

This accounts for the worst-case scenario of a simultaneous failure.

3. 25% of the total volume of all tanks

This rule applies when multiple tanks are not connected, and you’re looking at total site risk.

Example:

Total stored volume: 4,000L
Required bund capacity = 1,000 litres (25% of 4,000L)

Compare this with the other methods—always choose the largest resulting value.

4. Volume of largest tank + 20 minutes of sprinkler flow

If your facility has a fire sprinkler system, this must be factored in.

Example:

Largest tank: 800L
Sprinkler flow rate: 50L/min
20 mins x 50L = 1,000L
Required bund = 800L + 1,000L = 1,800 litres

This allows for emergency runoff that would otherwise overflow the bund.

Don’t Forget Displacement

The tanks, drums or IBCs sitting inside your bund take up space, reducing how much liquid the bund can actually hold. You must add this displaced volume to your calculations to ensure compliance. Our drum storage and bunding options are designed with this in mind, giving you reliable capacity without compliance risks.

Example:

Bund internal volume = 1,200L
Tank occupies 150L of space
Effective bund capacity = 1,050L, which may not meet the 110% requirement

Factors That Affect Bund Capacity Selection

Several site-specific factors influence the bund capacity you need:

Type of liquid – Oils, fuels, acids, and chemicals have different risks and reactivity
Indoor vs outdoor – Outdoor bunds may need extra volume for rainfall or UV degradation
Temperature changes – Liquids can expand in heat, increasing spill risk
Container types – Drums, IBCs, and tanks all have different spill profiles
Fire safety systems – Sprinklers add significant runoff that must be captured

Using the right forklift drum handling equipment also reduces the risk of damage and leaks during transport.

Common Mistakes to Avoid

Avoid these frequent bunding errors:

Only using 100% of tank volume (not 110%)
Ignoring displacement caused by container size
Overlooking sprinkler discharge in fire-rated areas
Failing to apply interconnected tank rules
Misapplying the 25% rule as a default rather than comparing all methods

These mistakes can lead to regulatory fines, increased spill damage, and WHS breaches.

Tips for Choosing the Right Bunding Products

Verdex offers a wide range of bunding solutions to suit different storage needs:

Portable bunds – Lightweight and ideal for field work or mobile storage
Spill pallets – Compact, compliant storage for drums or IBCs
Rubber or flexible floor bunding – Great for permanent warehouse setups
Custom bunds – Designed for your exact tank sizes and site layout

Stay Compliant: Know the Australian Standard (AS 1940-2004)

The AS 1940-2004 – The storage and handling of flammable and combustible liquids outlines bunding requirements across a range of substances and container types. It emphasises secondary containment, spill capture, and fire protection. Always cross-check with your local EPA and WHS regulations, as regional requirements may vary.

Get Bunding Right the First Time with Verdex

Correct bund capacity isn’t just a good practice, it’s a legal requirement. Understanding how to calculate and apply the correct bund volume protects your staff, your business, and the environment. For help navigating standards and choosing the right bunding, reach out to Verdex, your trusted partner in workplace safety.

At Verdex, we supply compliant drum handling equipment and bunding solutions to help businesses manage spills and stay compliant and environmentally responsible. Whether you need spill pallets, or expert advice, our team can help.

Email us at sales@verdex.com.au
Or fill out our online contact form

Frequently Asked Questions

What is bund capacity?

Bund capacity is the total amount of liquid that a containment area (bund) can hold in the event of a spill. It ensures leaks from tanks or drums don’t escape into the environment or workspace.

What is the 110% rule for bunding?

The 110% rule means your bund must hold at least 110% of the volume of the largest tank stored within it. This is a key guideline under AS 1940 and helps ensure full containment in a worst-case spill.

Why is bund capacity important?

It’s critical for safety, environmental protection, and legal compliance. Inadequate bunding can lead to hazardous spills, WHS breaches, and large fines from environmental regulators.

Do I need to include the volume displaced by tanks sitting inside the bund?

Yes. Tanks and drums take up space inside the bund. You must factor in their displacement volume to ensure the bund still has enough room to contain a full spill.

What is AS 1940 and how does it relate to bunding?

AS 1940 is the Australian Standard for storing flammable and combustible liquids. It outlines bunding requirements, including minimum volume calculations, fire safety, and maintenance procedures.

How to Calculate Bund Capacity To Meet Australian Standards

Why Bund Capacity Matters