What typically precedes combustion in materials?

Combustion is a rapid chemical reaction that typically involves the reaction of a fuel with an oxidizer (usually oxygen in the air) and produces heat and light. Before combustion can occur, certain processes must take place in the material being burned, one of which is pyrolysis.

Pyrolysis refers to the thermal decomposition of materials at elevated temperatures in the absence of oxygen. This process breaks down complex organic molecules into simpler compounds and gases, often producing volatile substances that can ignite if the concentration and conditions are right. Pyrolysis is crucial because it essentially prepares the material for combustion by creating flammable gases and char, which can then react with oxygen.

This pre-combustion stage is necessary for materials that are solid or liquid at room temperature, as they need to undergo this transformation to become gaseous or more reactive substances. Understanding pyrolysis is essential for fire investigators because it helps explain how and why certain materials ignite and burn in specific ways.

While other processes like evaporation, chemical alteration, and oxidation may play roles in combustion scenarios, they are not the direct decomposition process that typically occurs prior to combustion as pyrolysis is. Evaporation involves the transition of a liquid to a vapor, which is not always a precursor to combustion.