What do the four quadrants of the NFPA 704 diamond mean?

Blue (left) is health hazard, red (top) is flammability, yellow (right) is instability/reactivity, and white (bottom) is special hazards. The three coloured quadrants use a 0–4 scale; white holds letter or symbol codes such as OX or W.

What does a 4 mean on the scale?

4 is the most severe level in each colour. Health 4 means very short exposure can cause death; flammability 4 means it vaporises and burns readily at normal temperatures; instability 4 means it can detonate or explosively react at normal conditions.

What do the white special-hazard codes mean?

Common codes are OX (oxidiser), W with a strikethrough (reacts dangerously with water), and SA (simple asphyxiant gas, used only for nitrogen, helium, neon, argon, krypton and xenon). Some jurisdictions also use unofficial codes like COR or ACID.

How is NFPA 704 different from the GHS or UN systems?

NFPA 704 is a US fixed-installation placard for emergency responders, rating acute hazards under fire conditions. GHS labels are for handling and supply, and UN classes are for transport. The three describe the same chemicals from different angles and are not interchangeable.

Does this tool run offline?

Yes. The full NFPA 704 rating descriptions are built into the page and decoding happens entirely in your browser. Nothing is uploaded or stored.

NFPA 704 Diamond Reference

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What the NFPA 704 diamond shows

The NFPA 704 placard — the familiar four-colour “fire diamond” — tells emergency responders the acute hazards of a chemical at a glance. The blue, red and yellow quadrants each carry a 0–4 severity number, and the white quadrant carries one or more special-hazard symbols.

How it works

The three coloured quadrants use the same 0–4 scale where 0 is minimal and 4 is the most severe:

Blue   = Health hazard
Red    = Flammability
Yellow = Instability / reactivity
White  = Special hazards (OX, W, SA, …)

A rating of 4 in any colour signals an extreme acute hazard under fire conditions. The white quadrant is not a number — it holds letter codes such as OX for an oxidiser or a struck-through W meaning the substance reacts dangerously with water.

This tool lets you pick each rating and prints the official meaning, so you can read a real placard or build one for a label.

Tips and example

A diamond reading blue 3, red 0, yellow 0, white W describes a substance that is seriously harmful to health, does not burn, is stable, but must not be mixed with water — anhydrous calcium oxide is a rough example. Note NFPA 704 rates the acute fire-response hazard; for supply labelling use GHS pictograms and for transport use the UN class.