The National Fire Protection Association (NFPA) has devised a voluntary marking system to alert firefighters to the characteristics of hazardous materials stored in stationary tanks and facilities. This system, known as NFPA 704, can also assist citizens visiting a site in identifying the hazard presented by the stored substance. Use of the system is voluntary, unless specified by local codes.

NFPA 704 is a standardized system, which uses numbers and colors on a sign to indicate the basic hazards of a specific material being stored in large containers. Health, flammability, reactivity, and special hazards are identified and rated on a scale of 4 to 0 depending on the degree of hazard presented by the material (Figure 2-1).

The rating of individual chemicals can be found in the NFPA “Guide to Hazardous Materials.” Other references such as the National Safety Council’s “Fundamentals of Industrial Hygiene” contain the NFPA ratings for specific materials. Such information can be used not only during an emergency, but also when long-term remedial activities require extensive evaluation.

The NFPA 704 system for hazardous materials was devised to provide at-a-glance information to response personnel on how a substance could be expected to react in the event of an emergency.