What is NFPA 704?

NFPA 704 provides a simple, readily recognized, easily understood system for identifying the specific hazards of a material and the severity of the hazard that would occur during an emergency response.

The system addresses the health, flammability, instability, and special hazards presented from short‐term, acute exposures that could occur as a result of a fire, spill, or similar emergency.

The system is characterized by the "diamond" that is a "square‐ on‐point" shape. It identifies the hazards of a material and the degree of severity of the health, flammability, and instability hazards. Hazard severity is indicated by a numerical rating that ranges from zero (0) indicating a minimal hazard, to four (4) indicating a severe hazard.

The hazards are arranged spatially as follows: health at nine o'clock position, flammability at twelve o'clock position, and instability at three o'clock position. In addition to the spatial orientation that can be used to distinguish the hazards, they are also color‐coded as follows: blue for health, red for flammability, and yellow for instability. The shades of red, blue, and yellow are not regulated, but should be contrasting colours. The hazard ratings may have coloured backgrounds with contrasting coloured numerals or coloured numerals with a white background.

The six o'clock position on the symbol represents special hazards and has a white background. The special hazards in use include W, OX and SA.  W indicates unusual reactivity with water and is a caution about the use of water in either firefighting or spill control response. OX indicates that the material is an oxidizer.  SA, indicates that the material is a simple asphyxiant gas (nitrogen, helium, neon, argon, xenon.)