Spontaneous combustion is caused by which of the following?

• A. Exposure to open flame
• B. A slow chemical reaction that generates heat
• C. Rapid oxidation caused by air exposure
• D. Electrical spark igniting vapors

Answer: (B)

Spontaneous combustion happens when a material oxidizes slowly, releasing heat. If that heat can’t escape, the temperature climbs until the material reaches its ignition point and catches fire on its own. That internal heat buildup from a slow chemical reaction with air is what makes it spontaneous.

This is why oily rags, hay, compost piles, or other absorbent materials can ignite without an external flame or spark—their oxidation produces enough heat to self-ignite if the heat isn’t dissipated. The other options describe heat coming from outside or a rapid burn once ignition occurs, which isn’t how spontaneous combustion works.