Which factor does NOT play a role in the ignition of structures by wildfire?

The correct choice reflects that human intervention does not directly contribute to the ignition of structures by wildfire. In wildfire dynamics, structures are typically ignited through natural physical phenomena rather than intentional human actions.

Direct flame contact involves flames from the wildfire coming into physical contact with the structure, leading to ignition. Burning embers, also known as "firebrands," can be carried by the wind and land on or near structures, igniting them as well. Radiant heat refers to the heat energy radiating from the fire; this can cause nearby materials to reach ignition temperatures even without direct contact.

In contrast, human intervention involves actions taken by individuals, such as attempts to extinguish fires or create firebreaks, which, while impactful in terms of fire management, do not inherently play a role in the ignition process itself. Therefore, the process of a wildfire igniting a structure is primarily influenced by natural elements and the characteristics of the environment rather than human actions or interventions.