NFPA 704

hazard symbol used by emergency personnel to identify the risks posed by hazardous materials


NFPA 704, also known as a Safety Square, is a diamond-shaped sign or picture that tells people about the hazards of a chemical compound.[1] 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.[2]

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.[3]

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.[3]

Flammability (red)[1]
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)[1]
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 very bad 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)[1]
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.[3]
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.[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 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.



  1. 1.0 1.1 1.2 1.3 "NFPA 704: Standard System for the Identification of the Hazards of Materials for Emergency Response". National Fire Protection Association. 2016. {{cite web}}: Missing or empty |url= (help)
  2. "Proposed Amendments on Revisions to the Recommended System for the Identification of The Fire Hazards of Materials / NFPA No. 704M — 1969" (PDF). Archived from the original (PDF) on 2016-03-03. Retrieved 2016-01-29.
  3. 3.0 3.1 3.2 3.3 3.4 "Frequently Asked Questions on NFPA 704" (PDF). National Fire Protection Association. Archived from the original (PDF) on July 16, 2017. Retrieved January 29, 2016.