Outdoor Bunded Storage.

Weatherproof construction with a roof or hard top, corrosion protection appropriate to the environment, drainage that keeps rainwater out of the sump, and locks and hinges rated for exposure.

Indoor units used outside corrode at the seams and the lock seizes, usually within a season or two.

A covered or hard-top unit is the reliable answer. Where a drain-down valve is fitted, it must be kept locked shut and only opened after checking the water for contamination.

Water in a bund reduces available containment and, if contaminated, becomes hazardous waste that must be disposed of accordingly.

For flammable and volatile substances, high and low level vents providing natural cross-flow. Outdoor siting makes ventilation easier to achieve than indoors, which is one reason flammable stores are usually external.

Vents must be weather-protected but never blocked — a louvred vent keeps rain out while maintaining airflow.

Separation depends on the substances and quantities, and is set through your fire risk assessment. For flammable liquid stores, guidance commonly starts at around four metres from occupied buildings and boundaries, reducing where fire-rated construction is used.

Also keep clear of drains, gullies and anything that would carry a spill off site.

Yes. The unit and its contents are heavy, and a level, load-bearing base prevents distortion that would compromise both the door seals and the sump.

An impermeable base also provides a further layer of protection if the sump itself is ever breached.

Many outdoor bunded stores have forklift pockets and lifting eyes and are designed to be moved. Check the empty weight and lifting arrangement before assuming.

The unit must be completely emptied before lifting — moving a store with liquid in the sump is both unsafe and likely to spill.