What causes most exposure fires?

Radiation is the primary cause of exposure fires because it involves the transfer of heat through electromagnetic waves, allowing it to move across spaces without the need for a medium like air or contact with a solid object. This heat can ignite combustible materials that are located further away from the original fire, leading to secondary ignitions.

While conduction and convection also play roles in fire dynamics—conduction transferring heat through direct contact and convection through the movement of heated air or gases—radiation often accounts for the most significant heat transfer in exposure scenarios, particularly in open areas where radiant heat travels efficiently. Understanding the various methods of heat transfer is crucial in fire behavior analysis and firefighting tactics, but in terms of exposure fires specifically, radiation is often the dominant factor that causes adjacent structures or materials to catch fire.