The five rules of safe segregation
- Acids away from bases. Neutralisation is exothermic; concentrated pairs can boil and spatter.
- Oxidizers away from anything that burns. Include solvents, wood, paper and plastics, not just chemicals.
- Water-reactives in dry cabinets only. A leaking sprinkler above sodium is a fire, not a rescue.
- Cyanides / sulfides away from acids. The reaction releases HCN or H2S at lethal concentrations within seconds.
- Peroxide-formers dated and rotated. Old ether that has crystallised on the cap can detonate when you turn the lid.
Compatibility matrix by hazard group
The matrix below is the practical version of NFPA 400 Table 5.3.2 and CLP Annex I. It's what an inspector expects to see reflected in your storage layout.
| Group | Examples | Keep away from | Why it matters |
|---|---|---|---|
| Strong acids | Sulfuric, hydrochloric, nitric, hydrofluoric | Bases, cyanides, sulfides, active metals, oxidizers | Violent neutralisation, toxic gas release (HCN, H2S), hydrogen generation |
| Strong bases | NaOH, KOH, ammonia solutions | Acids, aluminium, zinc, tin, halogenated organics | Exothermic reaction, hydrogen release, formation of chloramines |
| Oxidizers | Hydrogen peroxide, nitrates, permanganates, hypochlorites | Organics, solvents, reducing agents, metals, acids | Fire, explosion, chlorine gas release |
| Flammable liquids | Acetone, ethanol, toluene, isopropyl alcohol | Oxidizers, open flame, sparks, hot surfaces | Vapours ignite well below room temperature |
| Water-reactive | Sodium, potassium, calcium carbide, LiAlH4 | Water, aqueous solutions, humid air | Hydrogen release, fire, violent exotherm |
| Cyanides & sulfides | NaCN, KCN, Na2S | Any acid | Releases HCN or H2S — both lethal at ppm levels |
| Peroxide-forming | Diethyl ether, THF, dioxane, isopropyl ether | Air, light, heat, metals | Peroxides accumulate and detonate on distillation to dryness |
| Compressed gases | H2, O2, acetylene, chlorine | Cross-group cylinders (flammable vs oxidizer) | A leak in a shared cabinet can ignite or corrode neighbouring cylinders |
Common domestic and lab mistakes
- Bleach + ammonia → chloramine gas (severe respiratory damage).
- Bleach + any acid → chlorine gas.
- Hydrogen peroxide + acetone → acetone peroxide, a primary explosive.
- Nitric acid + organic solvents → ignition and, with alcohols, alkyl nitrates.
- Aluminium + strong base → hydrogen release (explosion risk in closed containers).
- Old ether bottle opened → peroxide crystals on the threads can detonate.
How to segregate in practice
- Separate cabinets for acids, bases, flammables and oxidizers — never one "chemistry cupboard".
- Secondary containment (bunded trays) inside each cabinet, sized for the largest container.
- Acids on the lowest shelf you can reach safely; never above eye level.
- Alphabetical shelving is a myth — segregate by hazard first, then order within a group.
- Compressed gases: flammable and oxidizer cylinders at least 6 m apart, or separated by a 30-minute fire wall.
Where SDSs tell you what's incompatible
Every SDS lists incompatible materials in Section 10 (Stability and reactivity), with storage rules cross-referenced in Section 7. If you only have five minutes, read Section 10.5 — the exact list of what NOT to store next to the product.
Frequently asked questions
What is chemical compatibility?
Chemical compatibility is the ability of two or more substances to be stored, transported or mixed together without triggering a dangerous reaction — fire, toxic gas release, violent heat, pressure build-up or corrosion of the container.
Which chemical groups must never be stored together?
The five classic incompatibility groups: (1) acids vs bases, (2) oxidizers vs organics/reducers/flammables, (3) water-reactives vs aqueous solutions, (4) cyanides/sulfides vs acids (releases HCN or H2S), and (5) peroxides vs heat, light or metals. Segregate them by cabinet, secondary containment or physical distance — never by shelf height alone.
Where do I find compatibility data on an SDS?
Section 7 (Handling and storage) and Section 10 (Stability and reactivity). Section 10.5 lists incompatible materials explicitly; Section 10.3 covers hazardous reactions; Section 10.4 lists conditions to avoid.
Is bleach and ammonia dangerous?
Yes — sodium hypochlorite (bleach) plus ammonia produces chloramine vapours, which cause severe respiratory damage. Bleach plus any acid (vinegar, hydrochloric acid, toilet cleaner) releases chlorine gas. These are two of the most common domestic accidents reported to poison control.
Can I store flammables next to oxidizers?
No. Oxidizers (peroxides, nitrates, chlorates, permanganates) can ignite organic solvents on contact and sustain fires that ordinary extinguishers can't suppress. Keep at least 6 m (20 ft) apart or use a dedicated fire-rated cabinet.