Which color on the NFPA 704 placard represents instability?

• A. Red
• B. Blue
• C. Yellow
• D. White

Answer: (C)

NFPA 704 uses a color-coded system to signal different hazard types, so responders can quickly gauge risks. The color in the section for instability (reactivity) is yellow. That yellow area tells you how likely the material is to undergo hazardous reactions under conditions like heat, shock, friction, or contact with incompatible substances. The numbers (0–4) in that area quantify how severe the reactivity is, with higher numbers indicating greater danger. The blue area denotes health, the red area denotes flammability, and the white area covers special hazards. So yellow is the color that represents instability.