What is a significant characteristic of fires at the decay stage?

In the decay stage of a fire, a significant characteristic is that heat release diminishes. This stage occurs after the peak of the fire's intensity, where the available fuel has mostly been consumed, leading to a reduction in the overall heat output. During this phase, the fire begins to burn more slowly and may transition into smoldering if there’s not enough fuel or oxygen to sustain combustion at a higher level. As the fire consumes the remaining fuel, the rate of combustion decreases, which is evident in the drop in temperature and intensity of the flames.

While it is true that in the earlier stages of a fire, oxygen levels are crucial for maintaining combustion, in the decay stage, the amount of oxygen can become less effective due to the reduced amount of heat and fuel available. Fire spread, which is indicative of more active combustion, generally wanes as the fire enters this stage. Therefore, recognizing the diminishment of heat release as a defining feature of the decay stage allows for a better understanding of fire dynamics and behavior during this critical phase.