NFPA 704 Hazard Identification System
The National Fire Protection Association (NFPA) specifies a system for identifying the hazards associated with materials.
The hazard identification signal is a color-coded array of four numbers or letters arranged in a diamond shape. The blue, red, and yellow fields (health, flammability, and reactivity) all use a numbering scale ranging from 0 to 4. A value of zero means that the material poses essentially no hazard; a rating of four indicates extreme danger. The fourth value - white- shows special precautions - either water reactive or an oxidizing agent.
Red: Flammability Hazard
4 -- Materials with a flashpoint below 73°F and a boiling point above 100°F - Materials that will rapidly or completely vaporize at atmospheric pressure and normal ambient temperature, or that are readily dispersed in air and that will burn readily. Example: propane gas.
3 -- Materials with a flashpoint below 73°F and a boiling point greater than or equal to100°F, or a flashpoint above 73°F and less than 100°F - Liquids and solids that can be ignited under almost all ambient temperature conditions. Example: gasoline.
2 -- Materials with a flashpoint above 100°F, but not exceeding 200°F - must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Example, diesel fuel oil.
1 -- Materials with a flashpoint above 200°F - must be pre-heated to burn. Example: corn oil.
0 -- Materials which normally won't burn.
Blue: Health Hazard
4 -- Materials with an oral LD50 of less than or equal to 5 mg/kg - Material that on very short exposure could cause death or major residual injury. Example: hydrogen cyanide.
3 -- Materials with an oral LD50 above 5, but less than 50 mg/kg - Material that on short exposure could cause serious temporary or residual injury. Example: chlorine gas.
2 -- Materials with an oral LD50 above 50, but less than 500 mg/kg - Material that on intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. Example: ammonia gas.
1 -- Materials with an oral LD50 above 500, but less than 2000 mg/kg - Material that on exposure would cause irritation but only minor residual injury. Example: turpentine.
0 -- Materials with an oral LD50 above 2000 mg/kg - Material that on exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. Example: peanut oil.
Yellow: Reactivity Hazard
4 -- Material is capable of explosion or detonation at normal temperature and pressure. Example: trinitrotoluene (TNT).
3 -- Material is capable of explosion, but requires a strong initiating source, or the material reacts explosively with water. Example: fluorine gas.
2 -- Material undergoes violent chemical changes at elevated temperature and pressure or which reacts violently with water or which may form explosive mixtures with water. Example: calcium metal.
1 -- Normally stable, but can become unstable at elevated temperatures and pressures. Example: phosphorus (red or white).
0 -- Normally stable - Material that in itself is normally stable, even under fire exposure conditions, and is not reactive with water. Example, liquid nitrogen.
White: Special Precautions
W -- Material shows unusual reactivity with water (i.e. don't put water on it). Example: magnesium metal.
OX -- Material possesses oxidizing properties.