National Fire Rating System

drawing of the NFPA sign

The signs with four colored diamonds seen on buildings and trucks are a part of a system established by the National Fire Protection Association to warn fire and other emergency response personnel of potential dangers from hazardous materials within a building or vehicle. The numbers and symbols within the diamonds have the following meanings; complete descriptions are found in the Association's Recommendations for Identification of Fire Hazards of Materials.

Flammability (red, top square)

4 Very flammable gases or very volatile flammable liquids.
3 Can be ignited at all normal temperatures.
2 Ignites if moderately heated.
1 Ignites after considerable preheating.
0 Will not burn.

Health (blue, left square)

4 Can cause death or major injury despite medical treatment.
3 Can cause serious injury despite medical treatment.
2 Can cause injury. Requires prompt treatment.
1 Can cause irritation if not treated.
0 No hazard.

Reactivity (yellow, right square)

4 Readily detonates or explodes.
3 Can detonate or explode but requires strong initiating force or heating under confinement.
2 Normally unstable but will not detonate.
1 Normally stable. Unstable at high temperature and pressure. Reacts with water.
0 Normally stable. Not reactive with water.

Specific Hazard (white, bottom square)

OX Oxidizing agent.
W Water reactive.
radiation hazard symbol Radioactive.
biohazard symbol Biohazard.
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