Final answer:
In the NFPA diamond-shaped sign rating system, the blue quadrant on the left represents the health hazard of the substance.
Step-by-step explanation:
In the NFPA diamond-shaped sign rating system, the left-most quadrant is colored blue and represents the health hazard. This quadrant provides key information about potential health risks posed by a substance, helping ensure safety in environments where such substances are used or stored. The blue quadrant is part of a broader system that also includes a red quadrant for flammability hazards, a yellow quadrant for reactivity hazards, and a white quadrant for special hazards. Each hazard is rated on a scale from 0 to 4, with 0 indicating no hazard and 4 representing extreme hazard.