What is an indicator that a fire has reached the fully developed stage?

The indicator that a fire has reached the fully developed stage is that it requires additional fuel or oxygen to grow. When a fire has fully developed, it has consumed all available fuel within its vicinity and is burning at its maximum intensity. At this stage, the fire is characterized by a large volume of flames, significant heat production, and often high levels of smoke.

In a fully developed fire, the fire is essentially stable; it has reached a point where it is not gaining or losing intensity without the introduction of more fuel or oxygen. This means that the fire is no longer in the growth stage where it might be easily controlled or where visible flames could significantly decrease. While various factors may temporarily influence the fire behavior, the key characteristic of needing additional resources to grow signifies that the fire is at a fully developed stage.