What does thermal decomposition result from?

Thermal decomposition is a chemical process that occurs when a substance breaks down into simpler compounds or elements as a result of heat. Pyrolysis is a key mechanism that involves the thermal decomposition of organic material. During pyrolysis, the material undergoes an irreversible change in its chemical composition, characterized by the breaking of molecular bonds and the formation of volatile substances like gases, tars, and char.

Option B correctly identifies that this irreversible change in chemical composition is a direct result of pyrolysis, linking thermal decomposition to the application of heat in a way that alters the material fundamentally. Understanding this process is crucial for fire investigators, as it explains how different fuels behave under extreme heat and informs their assessment of fire patterns and origins.