In which stage of a fire does a backdraft occur?

A backdraft occurs during the decay stage of a fire. This stage is characterized by a significant reduction in the availability of fuel and oxygen, which leads to a decline in fire intensity. However, if there is a sudden influx of oxygen (such as opening a door or a window), the combustion can be reignited explosively. This phenomenon occurs because the unburned gases that accumulated in the fire environment can ignite rapidly when oxygen is introduced, resulting in a backdraft. During the decay stage, the fire has used up most of its available fuel and is transitioning to being extinguished, but the conditions can become dangerous if fresh oxygen is introduced unexpectedly.

In contrast, the other stages, such as incipient and growth, focus on the initial development and the expansion of the fire respectively, where the fire is actively consuming materials and has not yet entered a phase of decline. The fully developed stage represents a time when the fire is at its peak intensity, with little potential for the sudden explosive event characteristic of a backdraft.