How chemical storage compatibility works
Two chemicals are incompatible when mixing them — even accidentally, from a leak or a shared spill tray — produces a dangerous result: heat, fire, an explosion, a violent reaction, or a toxic/flammable gas. The standard way to decide is the reactivity-group method in EPA's Method for Determining the Compatibility of Hazardous Wastes (EPA-600/2-80-076): assign each chemical to a reactivity group, then look up the consequence of mixing those two groups. This tool maps the most common workplace chemicals into 12 practical groups and gives you the verdict plus the action to take.
What the compatibility codes mean
| Code | Meaning | What to do |
|---|---|---|
| H | Heat / violent reaction | Segregate; no shared spill containment. |
| F | Fire hazard | Never co-locate; separate fire-rated storage. |
| GT | Toxic gas | Never co-locate; separate fire-rated storage. |
| X | Do not mix – keep separate | Never co-locate; separate fire-rated storage. |
| OK | Generally compatible (use normal precautions) | Store normally; keep labeled and contained. |
The 12 hazard groups in this matrix
| Group | Typical examples |
|---|---|
| Mineral acids | Sulfuric, nitric, hydrochloric, phosphoric, chromic acid, muriatic acid |
| Organic acids | Acetic acid (vinegar), formic, citric, oxalic, propionic acid |
| Bases | Sodium hydroxide (lye), potassium hydroxide, ammonia, lime, cement |
| Oxidizers | Hydrogen peroxide, bleach (hypochlorite), nitrates, permanganates, perchlorates, pool chlorine |
| Flammables | Gasoline, acetone, alcohols, paint thinner, diesel, propane, solvents |
| Water-reactive | Sodium/potassium metal, calcium carbide, lithium, acid chlorides, some hydrides |
| Pyrophorics | White phosphorus, alkylaluminums, finely divided metals, silane |
| Peroxides | MEKP, benzoyl peroxide (fiberglass/resin hardeners), cumene hydroperoxide |
| Sulfides | Sodium sulfide, sodium bisulfite, metal sulfides |
| Cyanides | Sodium cyanide, potassium cyanide, cyanide plating salts |
| Chlorinated | Methylene chloride, chloroform, trichloroethylene, perchloroethylene |
| Inert | Sand, salts, glass, inert solids, argon. NOT water-based products — anything aqueous (latex paint, aqueous detergent) counts as water, not as inert. And CO2 and nitrogen are not inert toward burning metals: CAMEO warns CO2 must never be used on a metal fire, and lithium burns in nitrogen. |
The dangerous pairs to never store together
| Group A | Group B | Code | Why |
|---|---|---|---|
| Oxidizers | Flammables / solvents | F | Bleach or pool chlorine stored next to gasoline, acetone, or paint thinner can ignite. |
| Mineral acids | Cyanides | GT | Acid contacting a cyanide salt releases hydrogen cyanide (HCN) — rapidly fatal. |
| Mineral acids | Sulfides | GT | Acid contacting a sulfide releases hydrogen sulfide (H₂S) — toxic at low ppm. |
| Acids | Bases / caustics | H | Concentrated acid + caustic neutralize violently, spattering and boiling. |
| Oxidizers | Organic peroxides | F | Both are strong oxygen sources; co-storage escalates a fire dramatically. |
| Water-reactives | Acids / oxidizers | X | Sodium, calcium carbide, and acid chlorides react with moisture and acids. |
Worked examples
Example 1 — Pool chlorine and a gas can in the same shed. Calcium hypochlorite is an oxidizer; gasoline is a flammable. The matrix returns F (fire hazard) — a do-not-co-locate verdict. Action: move the chlorine to a separate, cool, dry, non-combustible area away from all fuels and reducers.
Example 2 — A drum of muriatic (hydrochloric) acid beside sodium-sulfide tablets. Mineral acid + sulfide returns G (toxic gas): the pair can release hydrogen sulfide (H₂S), which is dangerous at single-digit ppm. Action: segregate into separate secondary containment so a leak of one can never reach the other, and verify against SDS Section 10.
Does OSHA require chemical segregation?
OSHA's Hazard Communication Standard (29 CFR 1926.59 (adopts 29 CFR 1910.1200)) is about labels, safety data sheets, and training — it does not by itself impose a storage-segregation rule. The standards that govern hazardous-material storage are 29 CFR 1926.152 (construction); 29 CFR 1910.106 (general industry) for flammable and combustible liquids. In general industry, 29 CFR 1910.176(c) requires storage areas to be kept free from “accumulation of materials that constitute hazards from tripping, fire, explosion, or pest harborage” — a housekeeping rule, not a segregation rule for incompatible chemicals. The practical workflow inspectors expect: read each chemical's SDS Section 7 (handling & storage) and Section 10 (stability & reactivity / incompatible materials), then segregate using a compatibility method like EPA-600/2-80-076 — exactly what this tool automates.
What to do next
- Build a segregation map of your storage area. Group chemicals by reactivity class, then keep dangerous pairs in separate cabinets, rooms, or spill trays.
- Don't share secondary containment across incompatible groups — a single spill tray that catches an acid and a cyanide defeats the whole purpose.
- Label and date everything, and verify each pair against the actual SDS — group-level guidance is a screen, not a substitute for the product's Section 10.
- Download the printable matrix (PDF) above for the storage room wall, and confirm placements with your EHS lead.
Frequently asked questions
What do the compatibility codes mean?
H = Heat / violent reaction; F = Fire hazard; GT = Toxic gas; X = Do not mix – keep separate; OK = Generally compatible (use normal precautions). These codes follow EPA 600/2-80-076 and standard chemical segregation charts. Always consult your SDS and institutional EHS for site-specific storage.
Does OSHA require chemical segregation by compatibility?
OSHA's Hazard Communication Standard (29 CFR 1910.1200, adopted for construction by 1926.59) covers labels, safety data sheets, and training — it does not itself impose a chemical storage-segregation requirement. Flammable and combustible liquid storage is regulated separately under 29 CFR 1926.152 (construction) and 29 CFR 1910.106 (general industry). To plan segregation and secondary containment, employers use SDS Sections 7 (handling and storage) and 10 (stability and reactivity) together with a compatibility method such as EPA-600/2-80-076.
Can I store oxidizers next to flammables?
No. Oxidizers and flammables are incompatible (code F = fire hazard). Store them in separate cabinets or areas. The same applies to acids and bases (H), and mineral acids with cyanides or sulfides (GT = toxic gas risk). Use this matrix as a quick check; follow your facility's EHS policy.
Where does this compatibility data come from?
The matrix is based on EPA's Method for Determining the Compatibility of Hazardous Wastes (EPA-600/2-80-076) and aligned with institutional segregation tables (e.g., NIH, university EHS). Key pairs (acids-bases, oxidizers-flammables, acids-cyanides/sulfides) are verified against these sources.
When the chart isn't enough: enforcing segregation on a live jobsite
A printed matrix works in the storage room. It stops working the moment a delivery lands on the wrong site, or a foreman adds a product to a jobsite from the office without walking the cage first. That is the gap HazComFast closes: when a chemical is assigned to a jobsite, it is checked against what is already stored there, and a high-risk pair is stopped at that moment, instead of showing up on a report the next morning.
The block names the product already on site, the reaction type, and the verdict. The assignment does not go through: the box stays unticked until someone with authority decides otherwise. An administrator can override it deliberately; a site manager gets the same block with no override offered — the decision travels up, it doesn't get made at the tailgate. The screen is available in Spanish. And the rule set is maintained centrally, not compiled into the app: when a segregation rule is corrected, every jobsite gets the corrected verdict on the next screen it opens — with no update to install and no release to wait for.
Group-level screening remains a screen, here as anywhere: it does not replace the product's SDS Section 10, and it does not decide distances or cabinets for you. See how HazComFast handles hazard communication →
Sources & verification
- EPA-600/2-80-076 — A Method for Determining the Compatibility of Hazardous Wastes
- 29 CFR 1926.152 — Flammable liquids (construction)
- 29 CFR 1910.176 — Handling materials (storage housekeeping)
- 29 CFR 1910.1200 — Hazard Communication (SDS Sections 7 & 10)
Compatibility logic verified 2026-10-05. This matrix is an estimate for planning only — not legal advice and not a substitute for an individual product's SDS or your facility's EHS program.
Chemical inventory template →GHS label generator →SDS gap analyzer →Container size matcher →HazCom program generator →