On the other hand, the fire may develop into a steadily growing fire plume. This requires that the correct mix of fuel and oxygen is available to support combustion in the flaming regions.

Figure 5: Established burning on a couch

In this case, self-sustaining oxidation reactions are established and generate enough heat to feed new fuel vapour to the fire. The fire can grow as long as sufficient oxygen, fuel, and energy feedback are available so that combustion will continue, unless some outside force, such as a hose stream, acts upon it.

This phase in the life of a fire is commonly referred to as "established burning." For fuels found in many residential and commercial structures, a fire size (HRR) of 20 kW is often accepted as an indication that a fire has entered the established burning stage.