When solid fuels are heated, they begin to _____ and release fuel gases and vapors:

When solid fuels are heated, they undergo a process known as pyrolysis, where the material decomposes chemically due to heat. During this process, solid fuels break down and release fuel gases and vapors that can contribute to fire. This transition from solid to gas is critical because it is at this stage that flammable vapors are produced, which can be ignited in the presence of an open flame or sufficient heat.

Pyrolysis is an essential concept in fire science, as it marks the beginning of the fuel's transformation and plays a significant role in the fire development process. The other processes mentioned, such as ignition, burning, and smoldering, occur at different stages of combustion. Ignition refers to the moment when fuel reaches the temperature necessary to start burning, while burning involves the active combustion of those gases and vapors. Smoldering refers to a slower oxidation process that can occur in solid fuels without producing flames. However, it is the process of pyrolysis that is specifically responsible for the initial breakdown of solid fuels into gaseous products.