NFPA 704 is titled "Identification of the Hazards of Materials for Emergency Response."
NFPA 704 defines a visual information system used to provide basic hazard information for firefighters and other emergency responders. Commonly called the NFPA diamond, this visual system displays information that enables emergency responders and 911 operators to know the basic hazards of chemicals at the scene. It allows them to determine the appropriate response to the emergency and select the correct fire-fighting equipment, or determine if a hazmat team needs to be called in. Although it is sometimes used in conjunction with supplying other information, NFPA 704 only requires the NFPA diamond with its four ratings.
NFPA 704 specifies the use of a diamond divided into four equal sections. It identifies the hazards of a material based on three characteristics:
- Health Hazard (blue)
- Flammability (red)
- Instability (yellow)
The hazard level of each of these is ranked on a scale of 4 tom 0. NFPA 704 defines the rankings for each of the three categories.
Health hazards, under emergency conditions:
- (4) can be lethal.
- (3) can cause serious or permanent injury.
- (2) can cause temporary incapacitation or residual injury.
- (1) can cause significant irritation.
- (0) no hazard beyond that of ordinary combustible materials.
Flammability hazards, materials:
- (4) rapidly vaporize, or readily dispersed in air and burn readily.
- (3) produce hazardous atmospheres at almost any ambient temperature (readily ignited).
- (2) must be moderately heated before ignition occurs.
- (1) must be preheated before ignition can occur.
- (0) that will not burn under normal conditions.
Instability hazards, materials:
- (4) are readily capable of detonation or exploding.
- (3) given a strong initiating force, are capable of detonation of explosion.
- (2) readily undergo violent chemical change at elevated temperatures or pressures.
- (1) are normally stable, but can become unstable at elevated temperatures.
- (0) normally stable, even in fire conditions.
A fourth section of the NFPA 704 diamond, located at the bottom of the diamond, is used to identify special hazards such as water reactivity and oxidizing properties.
NFPA 704 specifies minimum sizes for the overall NFPA diamond, each of the four areas, and the size of the rating numbers.