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.
What each level means in practice
Health (blue)
| Rating | Meaning |
|---|---|
| 0 | No significant hazard under fire conditions |
| 1 | Slight irritation on short exposure |
| 2 | Intense or continued exposure could cause incapacitation |
| 3 | Short exposure could cause serious temporary or permanent injury |
| 4 | Very short exposure could cause death or serious residual injury |
Flammability (red)
| Rating | Meaning |
|---|---|
| 0 | Will not burn (e.g. water, concrete) |
| 1 | Must be preheated before ignition |
| 2 | Must be moderately heated or exposed to high temperature |
| 3 | Liquids and solids that can ignite under almost all conditions |
| 4 | Burns readily, rapid vapourisation at normal temperature |
Instability / reactivity (yellow)
| Rating | Meaning |
|---|---|
| 0 | Normally stable, not reactive with water |
| 1 | Normally stable but unstable at elevated temperature |
| 2 | Undergoes violent chemical change at elevated temperature |
| 3 | Can detonate with strong initiating source |
| 4 | Can detonate at normal temperature and pressure |
Worked examples
Blue 3, red 0, yellow 0, white W — a substance seriously harmful to health on short exposure, non-flammable, stable, but reacting dangerously with water. Concentrated sulphuric acid is one example: non-flammable, but water contact is hazardous.
Blue 2, red 4, yellow 0, white none — moderate health hazard, burns readily at room temperature. A typical flammable solvent like acetone sits in this range.
Blue 0, red 0, yellow 4, white OX — no health hazard, no flammability, but potentially explosive and an oxidiser — concentrated hydrogen peroxide at high concentrations approaches this territory.
How NFPA 704 fits with other hazard systems
NFPA 704 is designed for fixed installations and emergency response — it answers “how dangerous is this building in a fire?” GHS labels cover supply and handling and use pictograms with H/P phrases. UN hazard classes cover transport. All three systems can describe the same chemical from different angles and use different classification logic, so a NFPA 704 flammability 4 does not directly convert to a UN Class 3 flammable liquid rating, even though they often correlate.