NFPA 704

**NFPA 704**, also known as a **Safety Square**, is a tilted square-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.

## Codes

|colspan="2" style="color:black; background:#ff6666; width:75%; "|Flammability (red)|
| --- | --- |
|Will not burn. Examples: carbon tetrachloride, concrete, stone, and sand.||
|Must be heated for a long time before it will burn. Will not catch fire until it is heated to at least . Example: cooking oil.||
|Must be heated to somewhat high temperatures before it can catch fire. Will catch fire at temperatures between . Example: diesel fuel.||
|Can catch on fire in almost all temperatures. Examples: gasoline and acetone.||
|Can catch on fire in the air at regular room temperatures, and burn very easily. These chemicals catch fire at less than . Examples: acetylene, propane, and liquid hydrogen).||

|colspan="2" style="color:black; background:#6691ff; width:75%; "|Health (blue)|
| --- | --- |
|No danger to anyone's health. No special protections are needed. Examples: water, wood, and paper.||
|Exposure would cause minor pain or injury. Examples: acetone, sodium chloride (salt).||
|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.||
|Toxic. Breathing in, touching, or getting this material on the skin could cause very bad injury. Examples: chlorine, liquid hydrogen and carbon monoxide.||
|Very toxic. Getting even a very small exposure to this material could kill a person or hurt them very badly. Examples: cyanide and phosgene.||

|colspan="2" style="color:black; background:#fcff66; width:75%; "|Instability/reactivity (yellow)|
| --- | --- |
|Very stable, even during fires. Does not react with water. Example: helium||
|Usually stable, but can become unstable at high temperatures. Example: magnesium.||
|Can react violently with water, or form explosive mixtures with water. Examples: white phosphorus, potassium, and sodium.||
|Can explode if heated or shocked; or explodes when it touches water. Example: ammonium nitrate.||
|Can spontaneously explode at normal temperatures. Example: nitroglycerin.||
|colspan="2" style="color:black; background:#ffffff; width:50%; "|Special notice (white)|
| --- | --- |
|colspan=2|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.|
|colspan=2 style="color:black; background:#ffffff; width:50%; "|Non-standard symbols (white)|
| --- | --- |
|colspan="2"|Sometimes, other codes are put in the white triangle. These are not official NFPA codes.|
|**COR**|Corrosive (can burn through things). Example: sulfuric acid, hydrochloric 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, radium.|
|**CRY** or **CRYO**|Cryogenic (these chemicals create very low temperatures that can injure people). Example: liquid nitrogen, liquid oxygen.|

## Related pages

- Material Data Safety Sheet