Which phenomenon occurs due to the heat released in a fire?

The correct answer is pyrolysis. This phenomenon involves the thermal decomposition of materials when exposed to high temperatures, such as those found in a fire. In the context of fire, pyrolysis occurs when organic materials are heated, causing them to break down chemically before they actually reach the ignition point. This process typically produces flammable gases that can contribute to the combustion process, creating more heat and sustaining the fire.

To provide further context, the other options include processes that are not directly involved in the heat release aspect of a fire. Condensation refers to the transformation of vapor into liquid, which is not a direct consequence of heat release from combustion. Evaporation is the process of a liquid turning into vapor, which, while influenced by heat, does not directly relate to the materials being consumed in a fire. Combustion itself is the reaction between a fuel and an oxidant that produces heat and light, but it is not a phenomenon that occurs solely because of the heat released; instead, it is the result of the thermal breakdown and reaction of materials, which is what pyrolysis specifically describes.