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NFPA 704, also known as aSafety Square, is a tilted square-shapedsign orpicture that tells people about thehazards of achemical compound.[1] It was designed in 1960 by theNational Fire Protection Association, as a way of quickly tellingfirefighters and other emergency workers what kind of dangers might be nearby.[2]
The sign is made offour smaller diamonds: ared one on top, ayellow one on the right, awhite one on the bottom, and ablue one on the left. Numbers orsymbols in these boxes tell how dangerous thechemical is.
The red diamond tells howflammable the chemical compound is: how easily it catchesfire. The yellow diamond tells aboutreactivity: how quickly the compound reacts with other materials. (For example, some chemicals, likeammonium 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.[3]
The white diamond hascodes for "special hazards." For example, if a chemical likeammonium nitrate should not touchwater because it willexplode, a W with a line through it will be written in the white diamond.[3]
| Flammability (red)[1] | |
|---|---|
| 0 | Will not burn. Examples:carbon tetrachloride,concrete,stone, andsand. |
| 1 | Must be heated for a long time before it will burn. Will notcatch 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 attemperatures 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 andacetone. |
| 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, andliquid hydrogen). |
| Health (blue)[1] | |
|---|---|
| 0 | No danger to anyone's health. No special protections are needed. Examples:water,wood, andpaper. |
| 1 | Exposure would cause minorpain orinjury. 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 very bad injury. Examples:chlorine,liquid hydrogen andcarbon monoxide. |
| 4 | Very toxic. Getting even a very small exposure to this material could kill a person or hurt them very badly. Examples:cyanide andphosgene. |
| Instability/reactivity (yellow)[1] | |
|---|---|
| 0 | Very stable, even duringfires. 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, andsodium. |
| 3 | Can explode if heated orshocked; or explodes when it touches water. Example:ammonium nitrate. |
| 4 | Canspontaneously 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.[3] | |
| OX | The material is anoxidizer: it allows chemicals to burn without an air supply. Examples:ammonium nitrate andhydrogen peroxide. |
| ₩ | Reacts with water in an unusual or dangerous way; this chemical should not touch water. Examples:sodium andsulfuric acid. |
| SA | The chemical is a simpleasphyxiant gas. This means it decreases the amount ofoxygen in the air. This symbol is only used when the gas isnitrogen,helium,neon,argon,krypton, orxenon.[3] |
| Non-standard symbols (white) | |
|---|---|
| Sometimes, other codes are put in the white triangle. These are not official NFPA codes.[3] | |
| COR | Corrosive (can burn through things). Example:sulfuric acid,hydrochloric acid. |
BIO or | Biological hazard (a living thing, like avirus, that is dangerous). Examples:flu virus andrabies virus. |
| POI | Poisonous. Example:strychnine. |
RA,RAD or | Radioactive. Example:plutonium,radium. |
| CRY orCRYO | Cryogenic (these chemicals create very low temperatures that can injure people). Example:liquid nitrogen,liquid oxygen. |
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