What happens to the fire during the smoldering phase?

During the smoldering phase, the fire exhibits a low-burning state characterized by the combustion of materials in the absence of enough oxygen for full combustion. During this phase, the fire consumes a significant amount of the available oxygen, leading to a situation where there is not enough oxygen left to sustain a vigorous flame. This results in the fire suffocating itself, as the smoldering process typically produces minimal heat and no visible flames, relying instead on oxidative breakdown of materials.

Additionally, the smoldering phase is often the result of an earlier phase where the fire may have spread more rapidly and has now transitioned due to limited fuel availability or lack of ventilation. Unlike during an active flaming phase, where large flames and rapid spread are evident, the smoldering phase presents a subdued and less aggressive form of combustion that can sustain itself for a longer duration but ultimately leads to self-extinguishment as it depletes the oxygen that it needs to continue burning actively.