NFPA 704 Is a standard maintained by the U.S. National Fire Protection Association. It defines the “fire diamond” used by emergency personnel to quickly and easily identify the risks posed by nearby hazardous materials. This is necessary to help determine what, if any, specialty equipment should be used, procedures followed, or precautions taken during the first moments of an emergency response.
The four divisions are color-coded, with blue indicating level of health hazard, red indicating flammability, yellow (chemical) reactivity, and white containing special codes for unique hazards. Each of health, flammability and reactivity is rated on a scale from 0 (no hazard; normal substance) to 4 (severe risk).
Blue – Health
- 0 – Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. (e.g., peanut oil)
- 1 – Exposure would cause irritation but only minor residual injury. (e.g., turpentine)
- 2 – Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. (e.g., chloroform)
- 3 – Short exposure could cause serious temporary or residual injury. (e.g., chlorine gas)
- 4 – Very short exposure could cause death or major residual injury. (e.g., hydrogen cyanide)
Red – Flammability
- 0 – Will not burn. (e.g., water)
- 1 – Must be pre-heated before ignition can occur. (e.g., canola oil) Flash point over 93°C (200°F).
- 2 – Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. (e.g. diesel fuel) Flash point between 38°C (100°F) and 93°C (200°F).
- 3 – Liquids and solids that can be ignited under almost all ambient temperature conditions. (e.g., gasoline) Flash point below 38°C (100°F) but above 23°C (73°F).
- 4 – Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. (e.g., propane) Flash point below 23°C (73°F).
Yellow – Reactivity
- 0 – Normally stable, even under fire exposure conditions, and is not reactive with water. (e.g., liquid nitrogen)
- 1 – Normally stable, but can become unstable at elevated temperatures and pressures. (e.g., phosphorus)
- 2 – Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. (e.g., calcium)
- 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., fluorine)
- 4 – Readily capable of detonation or explosive decomposition at normal temperatures and pressures. (e.g., Nitroglycerin)
White – Special
- The white “special notice” area can contain several symbols:
- ‘W’ – reacts with water in an unusual or dangerous manner (e.g. Cesium)
- ‘OX’ – oxidizer
- ‘COR’ – corrosive; strong acid or base
- o ‘ACID’ and ‘ALK’ to be more specific.
- ‘BIO’ – Biohazardous
- The radioactive trefoil – is radioactive
- ‘CRYO’ – Cryogenic
Note: Only ‘W’ and ‘OX’ are officially part of the NFPA 704 standard, but other self-explanatory symbols are occasionally used in an unofficial manner.