Why secondary containment matters when you store liquids, and how to size it.
Storing fuel or chemicals in cans is only part of safe storage. If a can leaks, secondary containment is what stops the spill becoming an incident. This is general guidance; confirm your local rules.
Quick answer: What is secondary containment?
Secondary containment is a second barrier, a bund, drip tray or spill pallet, that holds what escapes from a leaking or toppled container. In England, outdoor oil containers above 200 litres need a bund for the greater of 110 per cent of the largest or a quarter of the total. A 20 litre can sits outside that rule.
Secondary containment is a bund, tray or spill pallet that catches what a container releases if it leaks or is knocked over. The container is the primary; the bund is the backup. Many jurisdictions require it for stored fuel and chemicals above a threshold volume.
Regulators care because the receiving environment is unforgiving in a way the quantity does not suggest. A few litres of diesel reaching a surface-water drain arrives in a watercourse essentially undiluted, spreads as a visible film over a large area and is expensive and slow to recover. That asymmetry, small spill and large consequence, is why containment is written as a requirement above a threshold rather than left to judgement.
Most sites have two drain systems, and the difference is the single most useful thing to know before siting a store. Foul drains run to treatment. Surface-water drains run, usually untreated, to the nearest watercourse. A spill into the first is a problem; a spill into the second is an incident with a regulator attached. If you do not know which gullies near your store are which, that is the survey to do before buying a bund.
A common rule is that a bund holds at least 110 per cent of the largest single container, or a set percentage of the total stored volume, whichever is greater. The extra allowance covers rainfall on an outdoor bund and the displacement of other containers. An outdoor bund needs freeboard on top of the working capacity so rain does not fill the spare volume you were counting on. Check the exact figure your regulator uses.
For England, the figure comes from the regulation itself. The Control of Pollution (Oil Storage) (England) Regulations 2001 apply to oil stored outside a building in any container of more than 200 litres, and require secondary containment of at least 110 per cent of that container. Where more than one container sits in the same bund, the requirement is 110 per cent of the largest or 25 per cent of the total stored volume, whichever is greater. Drums are the exception: a drip tray under them may hold 25 per cent of their combined capacity.
The two rules cross over sooner than people expect. Four 205-litre drums in one bund hold 820 litres. A quarter of that is 205 litres; 110 per cent of one drum is about 226. The largest-container rule wins, narrowly. Stand the same four drums on a drip tray and the drum provision asks for 205 litres. Add a 1,000-litre IBC to the bund and the answer jumps to 1,100 litres, because one large container now dominates. Our spill pallet sizing calculator runs the same arithmetic on your own mix.
A store of 20-litre jerricans is outside the regulations, because each can is under the 200-litre threshold. Bund one anyway where it sits near a drain. The same arithmetic shows why sizing off a single can undershoots: ten cans need 50 litres at a quarter of the total, against 22 litres at 110 per cent of one.
Scotland, Wales and Northern Ireland run their own equivalent instruments with the same architecture and different commencement dates, so a multi-site operator cannot assume one assessment covers the group. The English regulations exclude storage inside a building, any container of 200 litres or less, and oil used on a farm for agriculture, which falls under separate farm fuel rules above 1,500 litres.
Rain collects in any open bund left outside. For oil, the storage rules in England, Wales, Scotland and Northern Ireland bar any valve, pipe or opening that drains the bund, so pump the water out or keep the bund covered. A store of other flammable liquids may have a manual drain valve kept shut, which HSE’s HSG51 accepts. Either way, check the caught water for sheen or contamination before it goes anywhere. If it carries fuel or chemical, handle it as waste. A drain left open turns the containment into a straight path to the watercourse it was meant to protect.
Make the valve position visible and someone's job. A locked valve with the key held by a named person is a control; a valve nobody looks at is a decision taken once and never revisited. The check that catches the failure is whether anyone can say when the valve was last opened and what was released.
Match the containment to the volume. For a few cans, a spill pallet or drip tray under them catches drips and a knocked-over container, and a bunded cabinet suits a small indoor store. Larger volumes call for a fixed bund built into the floor or the tank area. Site any store away from drains, gullies and watercourses so a spill that beats the bund still has distance to travel.
For a jerrican store specifically, the sensible unit is a bunded spill pallet rather than anything built in. A four-drum pallet takes a useful number of 20-litre cans, holds its sump volume independently of the building floor, and can be moved when the store moves, which a poured concrete bund cannot. Where the store is indoors and the fuel is petrol, a bunded cabinet does the containment and the fire separation in one item, which is usually what a workplace assessment actually asks for.
Two sizing traps recur. The first is stacking: a bund sized for one layer of cans is undersized the moment somebody puts a second layer on top, and nothing about the pallet says so. The second is the sump being used as storage, for absorbent, funnels or a spare pump, which consumes the capacity the calculation assumed. Both are inspection findings rather than design faults, which is why the inspection list below matters as much as the purchase.
The bund has to resist what it might catch. A steel bund suits fuel; a chemical needs a bund lined or built in a compatible material, the same compatibility question as the container itself. A bund that the liquid eats through is no containment at all. See our compatibility guide, and match adapters and fittings to the liquid too when you decant with drum and IBC adapters.
A bund also meets its contents under worse conditions than a container does. It catches a spill neat, at whatever temperature the liquid was at, with no closure to limit evaporation and often with rainwater already in it changing the concentration. So a material that is rated for storing a chemical is not automatically rated for catching it: ask the compatibility question of the bund on its own terms.
When a can lets go, work the order: contain the liquid in the bund, absorb it with a spill kit rated for that liquid, then dispose of the used absorbent as the SDS directs. Keep the kit near the store, label containers by contents and date, and inspect for leaks and corrosion on a schedule. Good housekeeping catches a weeping can before it empties. The common mistakes are an undersized bund, an incompatible bund, a drain left open and no spill kit within reach.
Match the absorbent to the liquid as carefully as the bund. A general-purpose pad handles oil and fuel; an acid or alkali needs a neutralising absorbent, and using the wrong one turns a contained spill into a reaction in a tray. Keep the kit sized to the largest single container rather than to the shelf, because a kit that runs out halfway through is a kit that delayed the response.
An outdoor bund fills with rain, and a bund full of water has no capacity left for the spill it exists to catch. So it has to be drained, and the moment it is drained it becomes a potential discharge route to the environment, which is the thing the bund was protecting against.
The usual answer is a manually operated valve kept locked shut, opened only after the contents have been inspected, with contaminated water removed as waste rather than released. An automatic drain defeats the purpose: it will discharge fuel as readily as rain. A bund with a permanently open drain is not secondary containment.
Bunds fail quietly. A hairline crack in concrete, a perished seam on a polyethylene tray or a corroded joint drains the containment volume without anything looking wrong from above. The failure becomes visible during the spill it was meant to hold.
A sound, well-sealed container is the first line: a UN-coded can with an intact closure rarely reaches the bund. Read storing fuel safely.
A sound can with an intact closure prevents the event; a bund limits it after it has happened. Both are worth having and only one of them keeps the liquid saleable, the floor clean and the incident out of the report. Where a budget forces a choice, the money goes into the cans and the closures first.
The bund protects the ground. Nothing in a store protects the person decanting, and a splash reaches an eye in the time it takes to notice it. The main markets regulate the eyewash next to a chemical store, with prescriptive standards: ANSI/ISEA Z358.1 in the United States, EN 15154 in Europe, AS 4775 in Australia.
They agree on the numbers that matter. A fifteen minute flush, the time it takes to dilute a chemical off an eye. A unit that runs dry at four minutes cannot complete the flush. Tepid water, because cold water makes a casualty pull away from the stream before the fifteen minutes are up. Siting within ten seconds of the hazard, unobstructed, because a casualty who cannot see is not going to find a station down a corridor. Weekly activation, so the standing water in the line is not the first thing that reaches the eye.
Where there is a plumbed supply, a combination eyewash and shower covers both the eye and the body splash from one position. Where there is not, which covers most yards, construction sites and vehicles, a self-contained gravity-fed unit does the same job on a tank that has to be refilled and dated. Neither is a first aid kit item. It is life-safety equipment on a maintenance schedule.
The best containment is a can that does not leak, and the second best is a sump under it. For the specification detail behind a pallet, read choosing a spill pallet.
| Your use case | Recommended can | Why this one |
|---|---|---|
| Drums in storage |  Drum Spill Pallets |
Sumps to 488 litres, sized against the 110 per cent rule. |
| Drums being worked |  Drum Spill Decks |
Low enough to load by hand, grate shows a leak early. |
| IBC tanks |  IBC & Multi-Container Spill Pallets |
Linkable sumps pool capacity across a row of pallets. |
| Benches and small containers |  Bench Trays & Drip Trays |
From a 4 litre bench tray to a 145 litre pail pallet. |
| After the container fails |  Salvage Drums & Spill Response Storage |
An overpack moves a split drum; a cart keeps absorbent near. |
| The person, not the liquid |  Emergency Eyewash & Safety Showers |
Portable and plumbed units for a fifteen minute flush. |
| Sound fuel storage |  20L NATO Steel Fuel Can |
UN-coded steel with an intact vented closure. |
| Keeping the closure tight |  Caps, Closures & Gaskets |
The right gasket keeps liquid out of the bund. |
The common requirement is the volume of the largest single container in the store, plus a margin for rainfall where the store is outdoors. Some jurisdictions require a percentage of the total stored volume instead. Check the local rule, because the two approaches give very different answers for a large store.
In England, the oil storage regulations apply only to containers of more than 200 litres kept outside a building, so a store of 20-litre cans is outside them however many it holds. Farms follow separate rules once their fuel oil passes 1,500 litres in total. Below those lines a bund is still sensible wherever a spill could reach a drain or watercourse, and other jurisdictions set their own thresholds.
Polyethylene for acids, alkalis and most chemicals; coated or galvanized steel where fire resistance matters and the stored liquid is a hydrocarbon. Match the containment material to the stored liquid the same way you match the container, because a bund that dissolves is not containment.
Bunding is secondary containment: a wall, tray or spill pallet around stored liquid that catches what a container releases if it leaks or falls over. The container is the primary containment and the bund is the backup. Chemical bunding builds the bund from a material the stored chemical will not attack. Check that material against the liquid on its own terms, because a bund catches a spill neat, at whatever temperature it escaped and often mixed with rainwater.
A bund is secondary containment: a walled area, outer case or tray around a tank or a group of containers that holds whatever escapes if one leaks or fails. Its purpose is to keep fuel and chemicals off the ground and out of drains and watercourses. In England the oil storage rules require the base and walls of an oil bund to be impermeable to oil and water, with no valve, pipe or opening that could drain it.
The standards and regulations this page relies on, at their issuing body. Where a market rule is named here, check the current revision before you specify against it.
Last reviewed by Clarence Cheang, Co-Founder.
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