Incompatible chemicals are substances that react dangerously on contact — releasing heat, toxic gas, or fire. The core incompatible pairs are acids with bases, acids with cyanide or sulfide salts, acids with bleach, oxidizers with flammable solvents, and water-reactive materials with anything aqueous. Store each of these groups separately, in its own secondary containment, and never in a shared spill tray.
What chemicals should never be stored together?
This is the short list every receiving dock and chemical store should have posted. Each row is a pair that must not share containment, a shelf, or a spill pallet.
| Keep this… | …away from this | What happens if they mix |
|---|---|---|
| Strong acids (sulfuric, hydrochloric, nitric, phosphoric) | Strong bases (sodium hydroxide, potassium hydroxide, ammonia solutions) | Violent exothermic neutralization; boiling, spattering, container rupture |
| Any acid | Cyanide salts | Releases hydrogen cyanide gas |
| Any acid | Sulfide salts | Releases hydrogen sulfide gas |
| Any acid | Sodium hypochlorite (bleach) | Releases chlorine gas |
| Ammonia or ammonium salts | Sodium hypochlorite (bleach) | Releases chloramine gases |
| Oxidizers (nitric acid, hydrogen peroxide, permanganates, chlorates, perchlorates) | Flammable solvents, oils, greases, paper, wood | Ignition or explosion; no external spark required |
| Concentrated nitric acid | Acetic acid, acetone, alcohols, other organics | Violent oxidation, possible detonation |
| Water-reactive materials (sodium and potassium metal, calcium carbide, acid chlorides, anhydrides) | Water, aqueous solutions, damp air | Rapid heat release and flammable or corrosive gas evolution |
| Concentrated sulfuric acid | Water added into the acid | Violent boiling and acid spatter — always add acid to water, never the reverse |
| Peroxide-forming solvents (tetrahydrofuran, diisopropyl ether, 1,4-dioxane) | Air and light over time; also distillation to dryness | Forms shock-sensitive peroxides that can detonate |
| Flammable solvents (acetone, ethanol, toluene, xylene, IPA) | Ignition sources, oxidizers, compressed oxygen | Flash fire; vapors travel to remote ignition sources |
NOAA and EPA maintain the authoritative dataset behind these predictions in CAMEO Chemicals reactivity groups, which will predict the outcome for any two specific substances you enter.
Why does chemical segregation matter more than a locked cabinet?
Most storage incidents are not caused by someone deliberately mixing two chemicals. They are caused by a leaking drum, a cracked tote valve, or an over-full spill pallet that lets two spills find each other on the floor. A cabinet keeps material contained; segregation is what decides whether a small containment failure stays small.
That is the reason segregation is organized by hazard class rather than by alphabet, product line, or purchase order. Storing acetic acid next to acetone because both start with “acet” is exactly the failure mode segregation exists to prevent.
What are the main incompatibility groups?
Five groups cover most industrial inventories. Give each its own containment area.
- Flammable and combustible liquids — solvents, alcohols, aromatics, ketones.
- Oxidizers — nitric acid, peroxides, permanganates, chlorates, hypochlorites.
- Acids — mineral and organic. Nitric acid is an oxidizer as well and is usually isolated from other acids.
- Bases and caustics — sodium hydroxide, potassium hydroxide, amines, ammonia solutions.
- Water-reactive and air-reactive materials — alkali metals, carbides, acid chlorides, anhydrides.
Toxics and compressed gases are commonly handled as a sixth and seventh area depending on the site.
How does OSHA regulate flammable liquid storage?
OSHA’s flammable liquids standard, 29 CFR 1910.106, sets both the classification scheme and the cabinet limits. The flammable liquid categories are defined by flash point and boiling point:
| Category | Flash point | Boiling point |
|---|---|---|
| Category 1 | Below 73.4 °F (23 °C) | At or below 95 °F (35 °C) |
| Category 2 | Below 73.4 °F (23 °C) | Above 95 °F (35 °C) |
| Category 3 | At or above 73.4 °F (23 °C) and at or below 140 °F (60 °C) | — |
| Category 4 | Above 140 °F (60 °C) and at or below 199.4 °F (93 °C) | — |
Under 1910.106(d)(3)(i), a single storage cabinet may hold no more than 60 gallons of Category 1, 2, or 3 flammable liquids, or no more than 120 gallons of Category 4 flammable liquids. Under 1910.106(d)(3)(ii), the cabinet must limit its internal temperature to no more than 325 °F during a 10-minute standard fire test, and must be labeled in conspicuous lettering: “Flammable — Keep Fire Away.”
Read the standard directly at OSHA 29 CFR 1910.106. Note that the cabinet is a quantity limit, not a segregation strategy — a compliant cabinet full of mixed hazard classes is still a bad cabinet.
How should you physically separate incompatible chemicals?
- Separate secondary containment. Each hazard group gets its own spill pallet or bunded area. Never share a spill tray between acids and bases.
- Separate cabinets, not separate shelves. A shelf above another shelf shares a spill path.
- Corrosives low. Store acids and caustics at or below waist height so a dropped container does not reach eye level.
- Nitric acid alone. It behaves as an oxidizer; keep it out of the general acid cabinet.
- Date peroxide formers. Mark the receipt and open date on THF, ethers, and dioxane, and dispose of them on schedule.
- Label the storage area, not just the drum. Segregation only survives staff turnover if the area itself is signposted.
Every decision above starts with the SDS. Section 7 covers storage and Section 10 covers incompatible materials — see how to read a safety data sheet and how to read a GHS label on a chemical drum. Segregation rules also need to appear in your written program — see what a hazard communication program is.
Which RightPath products need segregated storage?
Most of the catalog falls into one of the five groups above. A few common examples:
- Sodium hydroxide 50% solution — caustic. Never share containment with any acid.
- Acetone — flammable liquid. Keep away from oxidizers; see how to store acetone safely.
- Mineral and organic acids across the bulk acid line — segregate from caustics and from cyanide and sulfide salts.
- Solvents across the bulk solvent line — see is acetonitrile flammable? for a worked example.
Every product RightPath ships arrives with an SDS, and the full SDS library is public so you can build your segregation map before the truck arrives. For classification during transport rather than storage, see DOT hazmat classes for solvents.
How do you get segregation-ready documentation from RightPath?
Send your product list and RightPath will return the current SDS set along with an all-in quote. If you are consolidating suppliers, ask for the documentation package up front rather than after delivery. Request bulk pricing.
Frequently asked questions
What are the five basic groups of incompatible chemicals?
Flammable and combustible liquids, oxidizers, acids, bases and caustics, and water-reactive or air-reactive materials. Each group needs its own storage area and its own secondary containment.
Can you store acids and bases in the same cabinet?
No. Acids and bases react exothermically. If both leak into a shared spill tray, the reaction boils and spatters corrosive liquid. Acids and bases require separate cabinets with separate secondary containment.
Why can’t you store bleach with acid?
Sodium hypochlorite reacts with acids to release chlorine gas. It reacts with ammonia and ammonium salts to release chloramine gases. Both are acutely toxic by inhalation.
Is nitric acid stored with other acids?
No. Nitric acid is a strong oxidizer as well as an acid, and it reacts violently with organic acids such as acetic acid and with solvents such as acetone and alcohols. Store it isolated from both the acid group and the flammables group.
How much flammable liquid can be stored in one cabinet?
Under OSHA 29 CFR 1910.106(d)(3)(i), a storage cabinet may hold no more than 60 gallons of Category 1, 2, or 3 flammable liquids, or no more than 120 gallons of Category 4 flammable liquids.
Where can I check whether two specific chemicals are compatible?
Use the NOAA CAMEO Chemicals reactivity tool, which predicts the reaction between any two substances in its database, and cross-check Section 10 of each product’s safety data sheet.