Bunded storage catches leaks and spills from drums, IBCs and tanks before they reach the ground or a drain. In England and Wales it is a legal requirement for many sites that store oil, and a sensible safeguard for most other hazardous liquids. This guide explains how bunds work, what the 110% rule means in practice and how to choose a unit that suits your site.
What is bunded storage?
Bunded storage is a way of keeping hazardous liquids in a container that has a second, leak-proof layer of protection around it. That outer layer is called a bund. It catches anything that escapes from the primary container, such as a drum, IBC or tank, so the liquid stays out of the soil and drains.
The result is a form of secondary containment. Businesses use it for oil, diesel and other fuels, strong chemicals and any liquid that would cause harm if it escaped. Some of it is a legal requirement, as the sections below explain.
How bunded storage works
A bund is a second layer of protection around a container. If the container leaks, splits or overflows, the liquid collects in the bund instead of spreading across your site.
The design depends on what you store. Drum and IBC units usually have a sump beneath the containers, so any spilled liquid drains through a grid or mesh deck and collects below. Bunded tanks work differently. They sit inside an outer case, or inside a bund built from masonry or concrete, which holds the contents if the tank fails.
Most bunded storage is used outdoors on industrial sites. A small spill pallet might sit beside a workshop door, while a walk-in store can hold dozens of drums. The largest stores are about the size of a small shed, so you will often need a forklift to load them.
Do you legally need bunded storage?
If you store oil, quite possibly. The Control of Pollution (Oil Storage) (England) Regulations 2001 set the rules in England. The Environment Agency's guidance on oil storage regulations covers England and Wales. It says you must follow the rules if you hold a container of 201 litres or more at a business, including marinas. The same applies at public sector buildings such as schools and hospitals. At a home, the threshold rises to 3,501 litres.
Enforcement matters here. The guidance warns that you could be fined or prosecuted. Beyond that, the Environment Agency can serve an anti-pollution works notice, which forces you to bring your store up to standard. The HSE plays a different role. It becomes involved on major hazard sites covered by the COMAH regulations. Its technical guidance for major hazard sites is also a useful reference on bund design.
Some containers are exempt. Underground tanks and refinery storage fall outside the rules, and so does oil kept inside a suitable building, as the FAQs below explain. Scotland and Northern Ireland have separate guidance from SEPA and DAERA, so check the local rules if you operate there.
The 110% rule and how to size a bund
Capacity is the detail that matters most. The bund must hold the contents of the container if it fails, with a margin on top. The Environment Agency sets the minimum capacities below.
| What you store | Minimum capacity |
|---|---|
| A fixed tank, mobile bowser, IBC or other single container | 110% of the container's capacity |
| Several tanks, bowsers or IBCs sharing one bund | The greater of 25% of their combined capacity or 110% of the largest |
| Drums on a drip tray | One quarter of the combined capacity of the drums the tray can hold |
| Hydraulically linked containers | 110% of their combined capacity, treated as one container |
Here is a quick example. A 2,500 litre tank needs a bund that holds 2,750 litres. Likewise, a single 1,000 litre IBC needs at least 1,100 litres. If two IBCs share one bund, 110% of the largest is 1,100 litres. That figure is higher than a quarter of their combined volume, so 1,100 litres is the minimum.
Drums follow a lower threshold, though it can surprise people. A drip tray built for four 205 litre drums must hold 205 litres, even if you only ever put one drum on it. A single 205 litre drum is also above the 201 litre limit, so it needs secondary containment too. Before you buy any unit, compare its stated sump capacity with the volume of your largest container.
What needs bunding
The oil rules cover a long list of liquids, including:
- Petrol, diesel and kerosene
- Biofuels and hydrotreated vegetable oil (HVO)
- Vegetable oils, including waste cooking oil
- Synthetic lubricating oils such as motor oil, and biodegradable lubricating or hydraulic oils
- Oils used as solvents, cutting fluids and insulating oils
- Liquid bitumen-based products, such as waterproofing and road coatings
Some substances sit outside these rules. LPG and non-oil solvents are excluded, and so is waste oil drained from vehicle engines, although you may still need an environmental permit for that.
Chemicals are a separate matter. Acids, alkalis, pesticides, fertilisers and industrial cleaning products are not oils, so the oil regulations do not cover them. A spill can still pollute soil and watercourses, however. Your COSHH assessment and the supplier's safety data sheets will tell you how to store each product. Bunding is a common way to contain these liquids, and the HSE recommends separate bunds for incompatible materials.
Design rules that catch people out
The Environment Agency sets out several design rules for bunds. A bund must be impermeable to oil and water. Its base and walls must not have a pipe, valve or opening that lets it drain. The bund must also seal any fill or draw-off pipe that passes through it. In addition, it must contain every part of the container and its fittings, such as valves.
Position matters too. Keep containers away from driveways, tanker turning circles and forklift routes, or protect them with barriers or bollards. If you fill a tank from a remote fill point outside the bund, use a drip tray to catch spills during delivery.
Rainwater is a practical problem for any open outdoor unit. It reduces the space available for a real spill, so remove it before it builds up. Alternatively, choose a unit with a cover or roof.
Benefits of bunded storage
Beyond compliance, a bund brings several practical benefits.
- Spill protection: Leaks, corrosion and overfilling at the fill point stay inside the bund. Single-skin tanks can corrode over time, so a bund gives you a second line of defence.
- Lower waste and clean-up costs: Fuel and oil are expensive to lose. A contained spill can be removed and disposed of properly, which keeps costs down.
- Security: Larger units are built like small outbuildings, with solid steel walls and sturdy locks that keep valuable liquids secure on site.
- Fire protection: If you store flammable liquids, a fire-rated unit helps limit the damage. Many of our units offer insulated one hour fire rating options.
- Flexibility: Multi-level stores hold large numbers of drums or IBCs, and many units can be made to order with different sizes, shelving and colours.
- Environmental protection: A contained spill stays out of soil and watercourses. You can then remove the liquid and dispose of it correctly.
Bunded oil tanks at home
Heating oil is the most common domestic use. As noted above, the Environment Agency's rules apply at a home only when a container holds 3,501 litres or more. Most household tanks therefore fall below the threshold. Even so, a bunded tank is worth considering, because a leak on a domestic plot can still reach soil, drains and neighbouring land. Your installer can confirm what applies to your property.
What happens without bunding
A leak from an unprotected container soaks into the ground or runs into a drain. Soil can lose its fertility, plants can die, and wildlife or pets can be poisoned if they come into contact with fuel or chemicals. Lost product costs money as well, particularly with fuel and oil.
The legal risk is just as real. For oil storage, the Environment Agency says you could face a fine or prosecution. It can also order you to bring your store up to standard. Preventing the spill in the first place is far simpler than dealing with the aftermath.
How to choose the right unit
Start with what you store and the containers it comes in. Work out the volume of your largest container, then check each unit's sump capacity against the rules above. After that, weigh up these points:
- Location: Outdoor units need weatherproofing, and a cover or roof keeps rainwater out of the sump.
- Access: Check the door size, ramps and fork access, particularly if you load drums or IBCs by forklift.
- Security and fire risk: Lockable steel units protect valuable liquids, and fire-rated options suit flammable ones.
- Material: Steel offers strength and security, while polyethylene resists corrosion. Always check the manufacturer's chemical resistance information against what you actually store.
- Room to grow: It is cheaper to buy the right size once than to add a second unit later.
Our range includes outdoor petrol and fuel storage, multi-purpose chemical storage units and a wide choice of drum and IBC stores. You can browse the full range here.
Looking after your bund
A bund only protects you while it is in good condition. Inspect it regularly for cracks, corrosion and damage, and clear spills straight away so they do not weaken the sump. Keep incompatible chemicals in separate bunds, label every container clearly and keep a spill kit close to the unit. Finally, remove rainwater promptly, because standing water leaves less room for a real spill.
Bunded storage FAQs
Does a double-skinned tank count as a bund?
Not on its own. The Environment Agency does not treat double-skinned or twin-walled tanks as secondary containment, because the second skin is there for strength. An integrally bunded tank is different, as the manufacturer builds the bund into the system.
Can I fit a drain valve to a bund?
Not for oil storage. The Environment Agency says a bund's base and walls must not have a pipe, valve or opening that lets it drain. Remove rainwater by hand or pump instead, and dispose of any contaminated water properly.
Do I need a bund if the oil is stored indoors?
Oil kept in a building with walls and a roof that would catch a leak is exempt from the oil rules. However, you may still need to meet fire safety measures under the Building Regulations, so contact your local council to check.
Buying from Storage N Stuff
Storage N Stuff supplies bunded units for drums, IBCs and tanks to businesses in many industries. Our team has 20 years of experience, so you can get clear advice on sizing and compliance. We also run a Price Promise, which means we will match the price if you find the same item cheaper elsewhere. We offer fast UK delivery too. If you have questions about capacity or fire ratings, speak to our team before you order.
