In the NFPA 704 system, which number indicates severe hazards?

In the NFPA 704 system, the number that indicates severe hazards is four. This system utilizes a diamond shape with a color-coded scale to represent various hazards associated with chemicals. Each number on the scale ranges from zero to four, with zero signifying no hazard and four indicating a severe hazard.

The designation of four (4) demonstrates a high level of risk involved with the substance, signifying that it could be life-threatening or involve severe health issues without proper precautions. This level warns responders to take extreme measures, including the potential for evacuation or specialized protective gear when handling the material. The clarity of the NFPA 704 system aims to ensure that emergency responders can quickly recognize the nature and severity of chemical hazards, enabling them to plan appropriate responses effectively.