NFPA - National Fire Protection Association - Fire Diamond

    drawing of the NFPA diamond
    What do the numbers and symbols on an NFPA fire diamond mean? The diamond is broken into four sections. Numbers in the three colored sections range from 0 (least severe hazard) to 4 (most severe hazard). The fourth (white) section is left blank and is used only to denote special fire fighting measures/hazards.
    the NFPA diamond

    Health Hazard

    the NFPA diamond

    Flammability

    4 - Will rapidly or completely vaporize at normal pressure and temperature, or is readily dispersed in air and will burn readily.

    3 - Liquids and solids that can be ignited under almost all ambient conditions.

    2 - Must be moderately heated or exposed to relatively high temperature before ignition can occur.

    1 - Must be preheated before ignition can occur.

    0 - Materials that will not burn.

    the NFPA diamond

    Instability1

    4 - Readily capable of detonation or of explosive decomposition or reaction at normal temperatures and pressures.

    3 - Capable of detonation or explosive reaction, but requires a strong initiating source or must be heated under confinement before initiation, or reacts explosively with water.

    2 - Normally unstable and readily undergo violent decomposition but do not detonate. Also: may react violently with water or may form potentially explosive mixtures with water.

    1 - Normally stable, but can become unstable at elevated temperatures and pressures or may react with water with some release of energy, but not violently.

    0 - Normally stable, even under fire exposure conditions, and are not reactive with water.

    1 Prior to 1996, this section was titled "Reactivity". The name was changed because many people did not understand the distinction between a "reactive hazard" and the "chemical reactivity" of the material. The numeric ratings and their meanings remain unchanged.
    the NFPA diamond

    Special Hazards

    OX This denotes an oxidizer, a chemical which can greatly increase the rate of combustion/fire.
    W with a bar Unusual reactivity with water. This indicates a potential hazard using water to fight a fire involving this material.
    Other symbols, abbreviations, and words that some organizations use in the white Special Hazards section are shown below. These uses are not compliant with NFPA 704, but you may see them on an MSDS or container label:
    ACID
    Acid, a corrosive material with a pH lower than 7.
    ALK
    Alkaline material, a base. Caustic, with a pH greater than 7.
    COR
    Corrosive (it could be either an acid or a base).
    corrosive, hand burned by acid
    Another symbol for corrosive.
    poison, skull and crossbones
    Poison or highly toxic material.
    Radioactive
    Radioactivity. Radioactive materials are hazardous when inhaled.
    Explosive
    Explosive material. Redundant with the Instability Rating.
    4 - Very short exposure could cause death or serious residual injury even though prompt medical attention was given.

    3 - Short exposure could cause serious temporary or residual injury even though prompt medical attention was given.

    2 - Intense or continued exposure could cause temporary incapacitation or possible residual injury unless prompt medical attention is given.

    1 - Exposure could cause irritation but only minor residual injury even if no treatment is given.

    0 - Exposure under fire conditions would offer no hazard beyond that of ordinary combustible materials.

    red bar 3
    This section is used to denote special hazards. There are two NFPA 704 approved symbols: