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NFPA 704, also known as a fire diamond, is a diamond-shaped sign or picture that tells people about the hazards of a chemical compound. It was designed in 1960 by the National Fire Protection Association, as a way of quickly telling firefighters and other emergency workers what kind of dangers might be nearby.
The sign is made of four smaller diamonds: a red one on top, a yellow one on the right, a white one on the bottom, and a blue one on the left. Numbers or symbols in these boxes tell how dangerous the chemical is.
The red diamond tells how flammable the chemical compound is: how easily it catches fire. The yellow diamond tells about reactivity: how quickly the compound reacts with other materials. (For example, some chemicals, like ammonium nitrate, explode when they touch water; this is an example of reactivity.) The blue diamond tells how dangerous the chemical is to a person's health. Each of these three diamonds - red, yellow, and blue - are given a score between 0 and 4. A score of 0 means there is no danger. A score of 4 means there is the worst possible danger.
The white diamond has codes for "special hazards." For example, if a chemical like ammonium nitrate should not touch water because it will explode, a W with a line through it will be written in the white diamond.
| Flammability (red) | |
|---|---|
| 0 | Will not burn. Examples: carbon tetrachloride, concrete, stone, and sand. |
| 1 | Must be heated for a long time before it will burn. Will not catch fire until it is heated to at least 93.3 °C (200 °F). Example: cooking oil. |
| 2 | Must be heated to somewhat high temperatures before it can catch fire. Will catch fire at temperatures between 37.8 and 93.3 °C (100 and 200 °F). Example: diesel fuel. |
| 3 | Can catch on fire in almost all temperatures. Examples: gasoline and acetone. |
| 4 | Can catch on fire in the air at regular room temperatures, and burn very easily. These chemicals catch fire at less than 22.8 °C (73 °F). Examples: acetylene, propane, and liquid hydrogen). |
| Health (blue) | |
|---|---|
| 0 | No danger to anyone's health. No special protections are needed. Examples: water, wood, and paper. |
| 1 | Exposure would cause minor pain or injury. Examples: acetone, sodium chloride (salt). |
| 2 | Could injure a person if they were exposed to a lot of this material at once, or a little bit of the material for a long time. Example: hydrogen peroxide. |
| 3 | Toxic. Breathing in, touching, or getting this material on the skin could cause serious injury. Examples: chlorine, liquid hydrogen and carbon monoxide. |
| 4 | Very toxic. Getting even a very small exposure to this material could kill a person or hurt them very badly. Examples: cyanide and phosgene. |
| Instability/reactivity (yellow) | |
|---|---|
| 0 | Very stable, even during fires. Does not react with water. Example: helium |
| 1 | Usually stable, but can become unstable at high temperatures. Example: magnesium. |
| 2 | Can react violently with water, or form explosive mixtures with water. Examples: white phosphorus, potassium, and sodium. |
| 3 | Can explode if heated or shocked; or explodes when it touches water. Example: ammonium nitrate. |
| 4 | Can spontaneously explode at normal temperatures. Example: nitroglycerin. |
| Special notice (white) | |
|---|---|
| The white "special notice" area can contain several symbols. There are only three official symbols that can go in this section. | |
| OX | The material is an oxidizer: it allows chemicals to burn without an air supply. Examples: ammonium nitrate and hydrogen peroxide. |
| ₩ | Reacts with water in an unusual or dangerous way; this chemical should not touch water. Examples: sodium and sulfuric acid. |
| SA | The chemical is a simple asphyxiant gas. This means it decreases the amount of oxygen in the air. This symbol is only used when the gas is nitrogen, helium, neon, argon, krypton, or xenon. |
| Non-standard symbols (white) | |
|---|---|
| Sometimes, other codes are put in the white triangle. These are not official NFPA codes. | |
| COR | Corrosive (can burn through things). Example: sulfuric acid. |
BIO or  |
Biological hazard (a living thing, like a virus, that is dangerous). Examples: flu virus and rabies virus. |
| POI | Poisonous. Example: strychnine. |
RA, RAD or  |
Radioactive. Example: plutonium. |
| CRY or CRYO | Cryogenic (these chemicals create very low temperatures that can injure people). Example: liquid nitrogen. |
