Safe Chemical Storage: A Segregation Checklist by Hazard Class

There isn't one single "chemical storage regulation" to check against. Storage sits across three different sources: DSEAR for substances that pose a fire or explosion risk, COSHH's general duty to control exposure for everything else hazardous, and HSE's own HSG71 guidance for the practical segregation grouping that ties back to a substance's GHS/CLP hazard classification. This checklist walks through what each one actually requires.

Start from the classification, not the shelf

Segregation decisions should follow the hazard classification on the label and in Section 2 of the substance's Safety Data Sheet, not the shape of the container or how the product happens to be used day to day. Two products that look similar on a shelf, a cleaning fluid and a pool chemical, for example, can carry entirely different classifications and need to be kept apart for entirely different reasons. Working from the classification first is what makes segregation decisions consistent rather than a judgement call made on the spot by whoever is unpacking a delivery.

Keep incompatible hazard classes apart

HSE's HSG71 guidance on chemical warehousing sets out the practical measures for segregating incompatible substances, built around the principle that certain hazard classes should never share a storage area, container run or drainage path. Oxidisers stored next to flammables, or corrosives next to reactive metals, turn a contained spill into a fire, an explosion or a toxic gas release rather than a cleanup job.

This applies to mixtures too, not just pure substances. A flammable solvent held inside another product, such as an aerosol or a diluted cleaning fluid, still carries the flammability hazard of what's dissolved in it, and shouldn't be stored in the same cabinet or bin as other flammable liquids simply because the container looks different.

Some incompatible pairings are common enough to be worth naming directly. Bleach and ammonia-based cleaners, stored side by side in general-purpose cleaning cupboards, can react to release toxic chloramine gas if containers leak into each other. Acids stored near cyanide-containing substances can generate lethal hydrogen cyanide gas on contact. Neither pairing looks obviously dangerous on a shelf, since both halves are everyday workplace products rather than exotic industrial chemicals, which is exactly why classification-based segregation matters more than instinct about what looks risky.

Flammable and oxidising substances have their own legal storage duty

Where a substance is classified as explosive, oxidising or flammable, DSEAR requires the employer's risk assessment to specifically cover the arrangements for its safe storage, alongside its handling and transport. This is a distinct legal duty from COSHH's general control-of-exposure requirement, triggered by the fire and explosion risk rather than a health hazard.

HSE's practical guidance puts numbers on this for workroom storage: no more than 50 litres of highly flammable liquid, or any flammable liquid with a flash point below the room's maximum ambient temperature, and no more than 250 litres of other flammable liquids with a flash point up to 60°C, should be kept in cabinets or bins within a workroom or working area (HSE guidance on storing flammable liquids in workrooms).

Beyond those quantities, HSE's guidance on storing flammable liquids in containers applies instead, covering dedicated storage areas outside the main working space.

Everything else falls under COSHH's general storage duty

Corrosives, toxic substances and other health hazards that aren't flammable or oxidising don't fall under DSEAR, but they're not exempt from control either. Regulation 7 of COSHH requires exposure to be prevented or adequately controlled, and how a substance is stored, whether that's a sealed container, a bunded area to contain leaks, or simply keeping it away from where food is prepared or eaten, is part of that control. There's no separate statutory storage checklist for these substances the way there is for flammables under DSEAR; the general duty to control exposure covers it.

In practice this usually means matching the container to the hazard rather than defaulting to whatever's on hand. Corrosive liquids need containers that won't be eaten through over time, acute toxicants are often kept locked away with restricted access rather than on an open shelf, and anything that could contaminate food needs physical separation from food storage and preparation areas, not just a different shelf in the same cupboard.

Ventilation and spill containment are part of the design, not an afterthought

HSG71 treats building design as core to safe storage, not a detail to fix later. Its guidance covers ventilation requirements for storage buildings and areas, and separately sets out the measures needed for spill control (HSE, HSG71). Poor ventilation lets vapours from flammable or toxic substances build up in a confined space; inadequate bunding turns one leaking drum into a spill that reaches the rest of the storage area, or a drain.

This matters most for substances classified as hazardous to the environment. A spill that reaches a drain or watercourse is not just a workplace safety issue at that point, it's a separate environmental exposure with its own legal consequences, which is why bunding and drainage control get treated as their own dedicated part of HSE's storage guidance rather than folded into general housekeeping advice.

Where and how much: dedicated storage versus workroom quantities

Small working quantities kept close to where a substance is actually used are one thing; bulk stock is another. Dedicated storage areas need their own ventilation, spill containment and, for flammables, distance from ignition sources, and they should be sized so that nobody has to fetch a full day's stock from a container designed for occasional top-ups. A cabinet rated for cleaning products in a workroom is not the same as a warehouse storage bay, and treating the two interchangeably is one of the more common gaps HSG71 flags in inspections. Access matters too: a storage area that's easy to reach for routine restocking but hard to walk past unnoticed if a door's been left open or a container's been left out is doing its job; one that's either locked away and inconvenient enough that people start keeping working stock elsewhere, or so casual that anyone passing through can help themselves, tends to fail in practice regardless of what the risk assessment says on paper.