NFPA 704, or the National Fire Protection Agency, in section 704 of their National Fire Code specifies a system used to identify hazardous materials. This system is actually a color coded diamond.
The diamond shape has red on top with the number 4, yellow to the right with the number 3, blue to the left with the number 2, and a white colored diamond at the bottom with a "W" and a horizontal line through it. Each color represents its own diamond within a bigger overall diamond shape. The blue, red and yellow fields are for health, flammability, and reactivity respectively. They all use a number ranging from zero to four, a value of zero means that the material poses essentially no hazard. A rating of four indicates that you are at extreme danger if exposed to such hazardous materials. The fourth value (the white diamond) tends to be a variable changing in its meaning, and what letters or numbers are written there.
The four divisions
The four divisions are encoded in four colors where blue indicates level of health hazard, red indicates flammability, yellow indicates reactivity (chemical), and white contains special codes for unique hazards.
|Health (Blue)||Flammability (Red)|
|0||Poses no health hazard, no precautions necessary and would offer no hazard beyond that of ordinary combustible materials (e.g., water, propylene glycol)||0||Materials that will not burn under typical fire conditions (e.g., carbon dioxide), including intrinsically noncombustible materials such as concrete, stone and sand. (Materials that will not burn in air when exposed to a temperature of 816°C (1500°F) for a period of 5 minutes.)|
|1||Exposure would cause irritation with only minor residual injury (e.g., acetone)||1||Materials that require considerable preheating, under all ambient temperature conditions, before ignition and combustion can occur (e.g., mineral oil). Includes some finely divided suspended solids that do not require heating before ignition can occur. (Flash point at or above 93.4°C (200°F)|
|2||Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury (e.g., diethyl ether)||2||Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur (e.g., diesel fuel) and some finely divided suspended solids that do not require heating before ignition can occur. Flash point between 38°C (100°F) and 93°C (200°F)|
|3||Short exposure could cause serious temporary or moderate residual injury (e.g., chlorine)||3||Liquids and solids (including finely divided suspended solids) that can be ignited under almost all ambient temperature conditions (e.g., gasoline). Liquids having a flash point below 23°C (73°F) and having a boiling point at or above 38°C (100°F) or having a flash point between 23°C (73°F) and 38°C (100°F)|
|4||Very short exposure could cause death or major residual injury (e.g., hydrogen cyanide, phosphine, carbon monoxide, sarin)||4||Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily (e.g., acetylene, diethylzinc). Includes pyrophoric substances. Flash point below 23°C (73°F)|
|Special (White)||Instability/Reactivity (Yellow)|
|The white "special notice" area can contain several symbols. The following symbols are defined by the NFPA 704 standard.||0||Normally stable, even under fire exposure conditions, and is not reactive with water (e.g. helium)|
|OX||Oxidizer (e.g., potassium perchlorate, ammonium nitrate, hydrogen peroxide)||1||Normally stable, but can become unstable at elevated temperatures and pressures (e.g. propene)|
||Reacts with water in an unusual or dangerous manner (e.g., cesium, sodium, sulfuric acid)||2||Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water (e.g., white phosphorus, potassium, sodium)|
|SA||Simple asphyxiant gas. Specifically limited to the following gases: nitrogen, helium, neon, argon, krypton and xenon.||3||Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked (e.g. ammonium nitrate, chlorine trifluoride)|
|4||Readily capable of detonation or explosive decomposition at normal temperatures and pressures (e.g., nitroglycerin, chlorine azide, chlorine dioxide)|
- NFPA 704 Wikipedia