What is an indicator of backdraft in a fire situation?

Pulsing smoke movement around small openings is a key indicator of backdraft in a fire situation. This phenomenon occurs when the hot gases inside a fire compartment cool down and create a vacuum effect, causing the smoke to be drawn back into the structure. The smoke may appear to be heaving or pulsing as it is drawn in and pushed out through tight spaces, indicating a potentially hazardous situation.

Recognizing this behavior is critical for firefighters as it signals that there is still a significant amount of unburned combustible materials and strained oxygen within the environment. If the compartment is suddenly opened, such as when a door or window is breached, the reintroduction of oxygen can result in an explosive combustion event, often referred to as backdraft.

While other indicators like loud cracking noises, a sudden increase in temperature, and flame propagation are associated with fire behavior, they do not specifically signify the imminent danger of backdraft in the same way that the movement of smoke does. Therefore, understanding the significance of pulsing smoke movement is essential for anticipating backdraft and ensuring firefighter safety.