During what stage of a fire does the amount of heat energy released begin to decline and become fuel controlled?

The stage of a fire when the amount of heat energy released begins to decline and becomes fuel controlled is known as the decay stage. During this phase, the available fuel in the fire environment is being consumed, leading to a reduction in heat output. As the fuel is depleted, the fire's intensity decreases, and eventually, it may extinguish itself if enough fuel is used up.

In this stage, the fire is no longer in a free-burning or oxygen-controlled state; rather, the fire can be limited by the fuel available, making it increasingly inefficient. This distinction is critical for firefighters, as understanding the fire's behavior at this stage can influence tactics for extinguishing the fire safely and effectively.

While the other stages—incipient, growth, and fully developed—are essential for understanding the progression and dynamics of a fire, they do not reflect the declining heat energy and fuel limitation characteristics that define the decay stage. In contrast, those earlier phases involve increasing or sustained energy release due to a steady supply of fuel and oxygen.