What does a blue section value of "4" represent in the NFPA 704 system?

In the NFPA 704 system, a blue section value of "4" indicates a high health risk. This system is designed to provide emergency responders with quick and easily interpretable information regarding the hazards associated with materials. The blue section specifically addresses health hazards, with a scale ranging from 0 to 4.

A value of 4 signifies that exposure to the material could result in serious or life-threatening effects, even with short exposure. This categorization is crucial for first responders to assess the level of risk and the necessary precautions when dealing with hazardous substances. In contrast, lower values in the blue section (like 0, 1, or 2) denote decreasing levels of health risk, with 0 representing no health risk at all.