Bunded Chemical Storage: What It Means and Why It Matters for Compliance 

Bunded chemical storage uses a second layer of containment to catch liquid if the main container leaks or spills. Instead of allowing a chemical to spread across a floor, reach drainage systems or escape into the surrounding environment, the bund is there to hold it in a controlled area.

That makes bunding an important consideration when hazardous liquids are stored on commercial and industrial sites. It is not, however, a shortcut to compliance. The right storage arrangement still depends on the chemicals involved, how much is being stored, where it is kept and the findings of the relevant risk assessment.

What Is Bunded Chemical Storage?

A bund is a form of secondary containment. The drum, tank, bottle, IBC or other vessel holding the chemical is the primary container. The bund sits around or beneath it, providing another barrier if that container fails.

Bunding can take several forms. A chemical store may have an integrated sump beneath its floor, while larger storage areas can use a bunded perimeter. Spill pallets provide another option for drums, IBCs and other containers where localised containment is appropriate.

Purpose-built COSHH containers can combine chemical storage and secondary containment within a dedicated unit, although the specification still needs to suit the substances being stored.

How Does Bunded Storage Work?

In simple terms, the primary container does the everyday job of holding the chemical. The bund is there if the primary container fails.

If a drum leaks, a container is damaged or liquid is spilt during storage, the secondary containment should retain that liquid rather than letting it travel beyond the storage area.

This only works if the containment itself is suitable. HSE guidance on packaged dangerous substances states that storage surfaces and containment need to be impervious, while materials used for indoor storage areas should be resistant to and compatible with what is being stored. Environment Agency guidance for permitted chemical waste facilities similarly requires tank bunds to be impermeable, stable and resistant to the stored materials.

Capacity also has to remain available. A bund partly filled with rainwater, debris or an earlier spill has less capacity available if another leak occurs. HSE advises removing rainwater to maintain bund capacity, while Environment Agency guidance calls for regular inspection and removal of accumulated contents where applicable.

Why Is Bunding Important for Chemical Storage?

The immediate benefit is straightforward: a leak is easier to manage when it stays in one place.

Without suitable containment, liquid can spread through a working area, enter drains or reach soil and water. That can turn a damaged container into a much larger safety or environmental problem.

Bunded storage can also make spill response more manageable. Staff can deal with the spill in a defined area rather than trying to control liquid that has already travelled across the site. HSE guidance specifically identifies bunding, sills and other containment arrangements as ways of preventing the uncontrolled spread of spillages.

There is an environmental side to this too. Environment Agency guidance for permitted chemical waste facilities requires storage and drainage arrangements to prevent contaminated run-off escaping and to keep incompatible wastes apart. The exact requirements depend on the site and activity, but the principle is the same: contain the substance before it can cause a wider problem.

Does COSHH Require Bunded Chemical Storage?

Not in every situation. COSHH requires employers to assess risks from substances hazardous to health and put appropriate controls in place. HSE guidance says that COSHH assessments should consider storage, use suitable containers, check labelling and separate incompatible materials. The regulations do not simply say that every chemical must be kept in a bunded store.

Bunding may form part of the controls identified for a particular workplace, particularly where liquid could escape from its primary container. That decision needs to reflect the chemical, quantity, storage arrangement and risks identified on site.

Environmental requirements are a separate consideration. For example, Environment Agency guidance for permitted chemical waste facilities requires adequate bunding of storage areas and sets specific requirements for bunds around tanks containing liquids that could harm the environment. Those requirements apply within that particular regulatory context and should not be treated as a universal COSHH rule for every business storing chemicals.

So, while bunding can support safer chemical storage, a bunded unit on its own does not make a workplace COSHH compliant.

How Much Should a Chemical Bund Hold?

There is no single bund capacity figure that can safely be applied to every chemical storage situation.

Requirements vary according to what is being stored, the type of container and the guidance or regulations that apply to that particular setting.

For example, HSE's HSG71 Chemical Warehousing guidance says that, for outdoor storage of packaged dangerous substances other than oil, an impervious sill or low bund should enclose at least 110% of the capacity of the single largest container within it. For internal bunded areas covered by the same guidance, HSE also gives a bunded volume of 110% of the largest receptacle.

That does not mean 110% is the correct figure for every form of chemical storage. Oil storage has its own requirements and Environment Agency guidance for tanks at permitted chemical waste facilities directs operators to the relevant CIRIA guidance when calculating capacity.

Before specifying a bund, check which rules and guidance apply to the substances, containers and site in question rather than starting with a percentage and assuming it fits.

What Should You Consider When Choosing Bunded Chemical Storage?

Start with the chemicals themselves. The store needs to work with what is actually going inside it, not simply provide enough floor space for the number of drums or containers you have.

Safety Data Sheets should be checked alongside the site risk assessment. HSE advises using SDS information when identifying chemical hazards and planning workplace controls.

Other points to consider include:

• Chemical type and quantity: Both affect the level and type of containment that may be appropriate.
• Compatibility: The primary container, bund and other materials within the storage area need to be suitable for the chemicals involved.
• Segregation: Incompatible substances should not be able to mix if a container leaks. HSE guidance specifically notes that spill containment should take segregation into account.
• Ventilation: Certain substances and storage arrangements may require suitable ventilation.
• Security: Access may need to be restricted depending on the hazards and the location of the store.
• Location: Think about nearby drains, vehicle movements, working areas and possible routes for escaped liquid.
• Inspection: Containers and containment need to remain in suitable condition, with any rainwater, spills or other material dealt with before they reduce usable capacity.

Different substances bring different considerations, which is why it is worth checking what can be stored in a chemical storage container before deciding on the specification you need.

Bunded Chemical Storage Containers for Commercial Sites

For businesses storing drums, containers or other hazardous liquids, a purpose-built chemical store can provide secure storage and secondary containment in one dedicated area.

ModCon's bunded COSHH containers are available with all-steel construction, secure single or double steel doors, steel louvre vents and bunding for leaks or spills. The current range also includes raised mesh galvanised flooring, signage, a drain plug, fork sockets and lifting eyes, with bespoke sizes available.

Those features still need to be matched to the intended use. In particular, the required containment capacity, chemical compatibility, ventilation and any segregation arrangements should be established before choosing the final specification.

Enquire About a COSHH Container

Choosing the Right Bunded Chemical Storage

There is more to choosing bunded storage than finding a unit big enough for the containers you currently have.

Look at the types and quantities of chemicals on site, how they need to be separated and who needs access to them. Location matters too, particularly where there are drains, vehicle movements, watercourses or other sensitive areas nearby. If the store will be outside, weather exposure and the way rainwater will be managed also need consideration.

Future use is worth thinking about at this stage. If storage volumes are likely to increase, or the mix of chemicals is likely to change, a made-to-measure unit may be more practical than working around a standard size later.

ModCon Cabins supplies purpose-built chemical storage in bespoke sizes as well as standard options. If you need a secure, bunded store for your site, explore our COSHH containers or speak to the team about what you plan to store.

FAQs

What Is the Difference Between Bunded Storage and a Standard Chemical Store?

Bunded storage includes secondary containment intended to catch liquid if the primary container leaks or spills. A standard chemical store may or may not include this feature.

Whether bunding is needed and what specification it requires should be decided using the substance's Safety Data Sheet, the site risk assessment and any relevant UK guidance. 

Can Different Chemicals Be Stored in the Same Bunded Area?

Sometimes, but only where the chemicals are compatible and the storage arrangement does not allow an incident involving one substance to create a problem with another.

Incompatible materials may need separate containment rather than simply being placed at opposite ends of the same bund. HSE guidance says containment arrangements should prevent liquid spills from reaching areas where incompatible materials are stored.

Check the relevant Safety Data Sheets and risk assessment before putting different chemicals within shared containment.

How Often Should a Chemical Bund Be Inspected?

Inspection frequency depends on the storage context, the condition of the equipment, the chemicals involved and the guidance that applies. For example, Environment Agency requirements for permitted chemical waste facilities specify daily inspections of storage areas, containers and infrastructure, while tank bunds require regular visual inspection and programmed engineering checks. Those frequencies should not automatically be applied to unrelated workplaces.

For other sites, inspection arrangements should be based on the risk assessment, relevant guidance and the manufacturer's information.

Can Bunded Chemical Storage Be Used Outdoors?

Yes, provided the storage is suitable for outdoor use and the substances involved.

Outdoor storage needs to account for weather as well as chemical containment. Rainwater can take up space inside an open bund and reduce the capacity available for a spill, so it needs to be managed appropriately. HSE guidance notes that rainwater should be removed to maintain bund capacity and suggests that a roof or cover may sometimes be worth considering.

The chemical's Safety Data Sheet, site risk assessment and relevant UK guidance should determine the final storage arrangement.