What symbol indicates an unusual reaction with water in the NFPA system?

What symbol indicates an unusual reaction with water in the NFPA system?

• A. W
• B. U with a circle
• C. Line W
• D. W with a line through it

Answer: (D)

The white area of the NFPA 704 diamond carries special hazard symbols. The letter W flags materials that react with water. When that W has a line through it, it specifically warns that the material has unusual reactivity with water and that water should not be used to extinguish or cool the material because it could react in hazardous or unpredictable ways. This cue helps responders choose appropriate, non-water-based methods and consult the material safety data sheet for handling instructions.

The white area of the NFPA 704 diamond carries special hazard symbols. The letter W flags materials that react with water. When that W has a line through it, it specifically warns that the material has unusual reactivity with water and that water should not be used to extinguish or cool the material because it could react in hazardous or unpredictable ways. This cue helps responders choose appropriate, non-water-based methods and consult the material safety data sheet for handling instructions.