Which statement best defines a self-heating material?

• A. Ignites spontaneously in air.
• B. In contact with air, self-heats.
• C. Reacts violently with water.
• D. Must be heated externally to burn.

Answer: (B)

Self-heating materials produce heat through a slow oxidation that happens when they are in contact with air. They don’t need an external energy source to start; the heat comes from the material itself as it reacts with oxygen. If this internally generated heat isn’t able to escape, the temperature can rise to the point of ignition, which is why these substances can start fires even without being heated externally. The statement that best defines this behavior is the one that says the material, in contact with air, self-heats.

The other options describe different hazards: igniting spontaneously in air points to a more aggressive pyrophoric behavior, reacting violently with water is a water-reactive hazard, and needing external heat to burn describes ordinary combustion rather than self-heating.