What is Spontaneous Combustion?

Spontaneous combustion refers to a situation where materials ignite without an external flame source due to heat generated from internal processes. Specifically, this phenomenon typically occurs when certain substances, such as oily rags or hay, undergo oxidation at a rapid rate, causing their temperature to rise. If the heat produced exceeds the material's ability to dissipate it, the temperature can continue to increase until ignition occurs.

This process is distinct from combustion initiated by external factors, which would require an external source of ignition, such as a spark or flame. While burning due to chemical reactions does involve some aspects of spontaneous combustion, the key element is the internal heat buildup in a confined space, which is why the correct answer focuses on the accumulated heat causing ignition.