Which of the following is an example of Division 4.2 self-heating substances?

• A. Activated Carbon, Oily Rags, Seed Cake
• B. Water
• C. Copper
• D. Glass

Answer: (A)

Self-heating substances are solids that can generate heat through internal exothermic processes, such as oxidation or decomposition, and may ignite without an external heat source if stored in bulk. Oily rags and seed cake are classic examples because the oils remaining in these materials can oxidize slowly; when many items are piled together, the heat cannot escape quickly and can build up to ignition. Activated carbon can also become self-heating under certain conditions, especially if contaminated with oil or moisture and left in contact with air, since its porous surface promotes oxidation and heat buildup. In contrast, water is a liquid and does not spontaneously generate heat in solid form, while copper and glass are stable inorganic solids that do not undergo self-heating under normal storage conditions.