Which quadrant of the NFPA 704 system indicates if a product is water reactive?

The correct answer is the blue quadrant of the NFPA 704 system. This quadrant specifically indicates health hazards, which includes the assessment of toxicity and potential reactions, such as water reactivity. In the NFPA 704 system, the blue quadrant is where you will find numerals that represent the degree of health risk associated with a material, including its potential reactions when in contact with water.

In contrast, the red quadrant indicates flammability, the yellow quadrant represents reactivity or instability, focused more generally on how the substance might react under certain conditions, and the white quadrant is used for specific hazards, such as radiation or acid. These distinctions are crucial for first responders to evaluate the necessary precautions when dealing with hazardous materials.