What is the most dangerous stage of a fire that can lead to a building collapse?

The most dangerous stage of a fire that can lead to a building collapse is during the fully developed stage of the fire. At this point, the fire has spread throughout the structure, creating extreme heat and consuming a significant amount of the available fuel. The integrity of the building is significantly compromised due to the duration and intensity of the fire, which weakens structural components like beams and floors.

During the fully developed stage, not only is there extensive burning, but also the potential for flashover increases, which can further contribute to the loss of structural integrity. This is typically when firefighters face the greatest risks due to the high levels of heat, toxic smoke, and the potential for sudden collapse.

While the decay stage can also present risks due to structural damage and a potential collapse from weakened materials, it is typically in the fully developed stage where the destructive impact of the fire is at its peak, leading to the highest probability of a catastrophic collapse.