Chemical Storage Segregation: Reading the Compatibility Matrix

Most chemical store rooms are organised by supplier or by purchase order, which is convenient for stock-taking and dangerous for everything else. Segregation by hazard class costs nothing but shelf rearrangement, and it is the control that prevents the incident where two spilled drums react with each other.

The incompatibility rules that matter

The two combinations that cause fatalities most often in industrial settings are acid with sulphide or cyanide, producing hydrogen sulphide or hydrogen cyanide, and hypochlorite bleach with acid, producing chlorine. Both are common textile and cleaning chemicals stored together in a great many plants.

Separation means distance or a barrier

Segregated is not satisfied by different shelves in the same cabinet. Acceptable separation is one of: a physical barrier with an appropriate fire rating, a separate bunded compartment, a separate room, or a distance of at least 3 to 5 metres with no shared drainage. Shared drainage is the detail people miss — two separated bunds that both drain to the same interceptor are not separated in a spill.

Secondary containment sizing

Bund capacity must be at least the greater of:
   (a) 110 per cent of the largest single container, or
   (b) 25 per cent of the total volume stored

Plus freeboard for firewater and rainfall if the area is not roofed.

For an outdoor bund, add the volume from the design rainfall event. A bund that meets the 110 per cent rule and then fills with rainwater has no capacity left when it is needed, which is why outdoor bunds need a controlled, normally-closed drain valve and a documented routine for emptying it.

The SDS sections that change your storage

• Section 7 — Handling and storage. The direct answer, including incompatible materials and temperature limits.
• Section 9 — Physical and chemical properties. Flash point drives flammable classification; vapour density above 1 means vapour accumulates at floor level and low-level ventilation is required.
• Section 10 — Stability and reactivity. Conditions to avoid and incompatible materials, stated explicitly.
• Section 5 — Firefighting measures. Tells you whether water is the wrong medium, which changes what extinguisher goes in that room.

Sections 7, 9 and 10 should be extracted into a one-page store-room summary for every chemical held. Nobody reads a 16-section SDS during a spill.

Spill response that works

1. Spill kits located at the store, not in a central safety office, with contents matched to what is stored — acid neutraliser where acids are held, not generic absorbent alone.
2. Quantities sized for the largest single container, not for a token 20-litre spill.
3. A written procedure that starts with evacuation and isolation, not with cleaning up.
4. Contaminated absorbent treated as hazardous waste with a documented disposal route. This is the step that fails most audits.

Housekeeping details that prevent most incidents

Keep containers closed and labelled in the original packaging wherever possible; decanted chemicals in unlabelled bottles cause a large share of exposure incidents. Never store liquids above eye level. Keep an up-to-date inventory with maximum quantities, because your fire service and your insurer both need it, and because it is the only way to notice that the store has quietly accumulated three times what the room was designed for.