Right arrow Bunded Zones and Sumps in Chemical Stores

Bunded Zones and Floor Interfaces in Chemical Warehouses

Q: Why do spills sit outside bunds instead of flowing into them?

Spills tend to sit outside bunds when floor falls around the bund do not lead toward the wall. Low spots and slight slopes away from the bund can hold or spread liquid outside the protected area rather than moving it into the bunded zone.

Q: What causes leakage at bund and floor interfaces?

Leakage commonly arises from unsealed joints, shrinkage cracks or local settlement at wall bases. These fine gaps can carry liquids at floor level even when the visible bund structure appears intact.

Q: How should sump levels relate to the surrounding floor?

Sumps should sit slightly below the surrounding floor, with falls that encourage liquid inflow. If they are too high they will only collect larger spills, while overly deep or poorly detailed sumps can be difficult to clean and maintain.

Q: Can we correct poor bund thresholds without rebuilding the walls?

In many cases thresholds can be rebuilt or resurfaced without altering the main bund walls. This allows height and shape to be restored at door lines while keeping disruption to a minimum, provided the works are planned around traffic and door clearances.

Q: How often should bunded floors and sump interfaces be reviewed?

Bunded floors and sump interfaces should be reviewed when product ranges or traffic patterns change and after any incident that tests containment. Periodic inspections focused on wall bases, thresholds and sump surrounds help identify issues before they affect performance during a real spill.

Q: How do bund and sump interfaces link to regulatory expectations?

Regulatory expectations cover how containment systems work in practice, which includes the behaviour of floor interfaces as well as bund walls and sumps. Showing that these details have been assessed and, where needed, improved supports the overall compliance case for the site.

In chemical storage warehouses, bund walls and sumps are only as effective as the floors that feed them. Small level changes, worn thresholds, poor joint detailing or cracked interfaces can all create paths that let liquids escape, bypassing structures that look correct on drawings. We approach bunded areas as a complete system within the wider chemical storage warehouse flooring design, so that slabs, toppings and interfaces work together to support containment in real incidents.

20 +

Years
Detailing Bunded Floors

Interfaces between floors, bund walls and sumps are where design intent is most often lost. Settlement at wall bases, shrinkage at slab joints or repeated drum and forklift movement can all disturb levels and open cracks along these edges. Those changes in turn alter spill paths, building on the effects described in our work on spill behaviour and containment and magnifying compatibility issues explored in acids, alkalis and solvent exposure. We take account of expectations for secondary containment in HSE COMAH guidance when reviewing how these interfaces have to perform over time.

How Floors Interact with Bunds and Sumps

Bunds and sumps rely on floors to guide liquids into the protected volume without leakage at edges or low points. If slab falls are wrong, liquids can run away from bund walls instead of toward them. If thresholds are worn or cracked, fluids may escape under doors or into neighbouring areas even when tank or store walls are intact. Sumps that sit slightly proud of the surrounding floor may never see flow until a large loss occurs, while low sumps with poor approach shaping can accumulate residues in corners that are difficult to clean.

On new sites, bund geometry and sump locations can be coordinated with falls during concrete slab installation, leaving enough allowance for toppings and chemically compatible finishes. On live facilities, resurfacing works are often used to rebuild thresholds, correct falls into sumps and repair joints along wall bases. In some lightly exposed areas such as bunded inspection bays, polished concrete may be suitable where ease of inspection and clean up is a priority and the chemistry is well controlled.

Floor Interface Factors that Affect Containment

Accuracy of falls toward bunded bays and sumps.
Condition of thresholds at doors and vehicle entrances to bunds.
Joint layouts and sealing where slabs meet bund walls.
Local settlement or cracking beneath wall bases and plinths.
Surface texture and cleanliness where spills must be recovered quickly.

Typical Problems at Bund and Sump Interfaces

Many bunds and sumps appear correct on paper but behave poorly in day to day operation, especially once traffic, drum handling and cleaning regimes have had time to influence the floors around them.

Low spots outside bund walls where liquids pool instead of flowing inside.

Worn or cracked thresholds that allow product to escape under doors.

Unsealed joints running along wall bases that act as unseen leak paths.

Sumps set too high relative to surrounds, so only large spills reach them.

Residue build up in corners inside bunds, driven by poor flow shaping.

Surface damage where aggressive products collect around sump grates.

Right arrow Our Approach

How We Improve Bund and Sump Floor Interfaces

STAGE 1

Surveying Levels, Joints and Wall Bases

We begin with a detailed survey of floor levels, joint layouts and wall base conditions around bunded zones and sumps. This includes checking how existing falls relate to the spill paths identified in the spill control review, noting where liquids would realistically travel during a leak. Joints, cracks and thresholds are mapped so that any changes in geometry since construction are taken into account.

Double arrows STAGE 2

Redesigning Falls and Interfaces to Support Containment

Using the survey data, we develop practical options for reshaping interfaces. This might involve regrading floors immediately outside bunds, rebuilding thresholds to a defined height, or installing chemically compatible joint details along wall bases. Sump surrounds can be reshaped so liquids are encouraged to flow into the collection point rather than into corners or back toward doors, supporting the chemical compatibility solutions described in the exposure assessment.

Double arrows STAGE 3

Implementing Phased Upgrades Around Live Storage

Chemical warehouses rarely have the luxury of shutting down entire bunded areas. We plan works so that individual bays, wall runs or door lines can be taken out of service in turn while storage is rearranged or decant operations are temporarily diverted. Resurfacing, joint treatment and threshold works are sequenced to keep containment performance at least as good as the original condition at every stage, with checks on flow behaviour before each section is handed back.

Getting Bund Thresholds to the Right Height

Thresholds must be high enough to contain expected spill volumes yet practical for traffic and housekeeping. We refine threshold levels and profiles so that routine movements remain workable while containment capacity is protected.

Controlling Flow into Sumps and Low Points

Sumps need floor shapes that encourage inflow rather than resist it. We adjust local geometry so liquids reach collection points predictably instead of pooling in corners or along wall bases, where leaks can remain unseen.

Protecting Interfaces from Chemical Attack

Interfaces are often exposed to the most aggressive products. We specify joint details, mortars and finishes at wall bases, thresholds and sump surrounds that match the chemistry and clean down regimes present on site.

Keeping Inspection and Maintenance Practical

Bunds and sumps are easier to inspect when interfaces are clear and accessible. Our designs support regular checks, residue removal and testing, so small changes are picked up before they become significant defects.

Get a Quote for Bund and Sump Floor Upgrades

We work with operators of chemical storage warehouses across the UK to improve bunded zones, sump interfaces and floor performance in real spill scenarios.

Email: info@warehouseflooringsolutions.co.uk
Phone: +44 7813 957982
Unit 38 Neath Abbey Business Park
Neath Abbey
SA10 7DR

Right arrow FAQ

Bunded Zones and SumpsCommon Questions

Why do spills sit outside bunds instead of flowing into them?

This usually happens when floor falls outside the bund are not aligned with the bund wall. Low spots just beyond the wall can hold liquid in puddles, while minor slopes away from the bund allow product to spread across the warehouse instead of moving inside the protected volume.

What causes leakage at bund and floor interfaces?

Leakage often results from unsealed or damaged joints along wall bases, shrinkage cracks that were not treated, or settlement that opens fine gaps. These paths are easy to miss during visual checks but can carry liquids at floor level even when the visible structure appears sound from above.

How should sump levels relate to the surrounding floor?

Sumps generally need to be slightly lower than the surrounding floor, with gentle shaping that encourages inflow. If they sit too high, only large incidents will reach them. If they are much too low without proper detailing, edges can become damage traps and cleaning becomes more difficult for routine housekeeping teams.

Can we correct poor bund thresholds without rebuilding the walls?

Often yes. Local resurfacing and threshold reconstruction can restore height and shape at door lines, bringing them back in line with containment expectations while leaving the main bund walls untouched. The key is to check how any change interacts with traffic and existing doors before works start on site.

How often should bunded floors and sump interfaces be reviewed?

Reviews are advisable whenever product ranges change, when significant traffic patterns alter, or after any incident that tests containment. Periodic inspections that specifically target wall bases, thresholds and sump surrounds help catch level changes or cracking before they affect performance during a real spill event.

How do bund and sump interfaces link to regulatory expectations?

Regulators look for containment that works in practice, not just in design documents. This includes the behaviour of floor interfaces, not only the size of bund walls or sumps. Demonstrating that these details have been assessed and, where needed, upgraded supports the overall compliance position for a chemical storage site.