Which statement correctly characterizes Class 4 flammable solids?

Which statement correctly characterizes Class 4 flammable solids?

• A. They require an ignition source only
• B. They burn exclusively with heat
• C. They are always liquids
• D. They ignite spontaneously or when in contact with water

Answer: (D)

Class 4 flammable solids are hazardous because they can ignite without an external ignition source and can also react with water to release flammable gases. That combination is what defines their risk: spontaneous ignition, or ignition triggered by contact with water. The statement that captures both of these behaviors is the best fit. The other descriptions don’t match: these materials aren’t defined by needing a flame or spark alone, they aren’t inherently liquids, and while some may react with water, the key point is the spontaneous or water‑activated ignition of solid materials.

Class 4 flammable solids are hazardous because they can ignite without an external ignition source and can also react with water to release flammable gases. That combination is what defines their risk: spontaneous ignition, or ignition triggered by contact with water. The statement that captures both of these behaviors is the best fit. The other descriptions don’t match: these materials aren’t defined by needing a flame or spark alone, they aren’t inherently liquids, and while some may react with water, the key point is the spontaneous or water‑activated ignition of solid materials.