What is an explosion resulting from the introduction of fresh air into an oxygen-depleted atmosphere called?

The situation described in the question refers to a phenomenon known as backdraft. A backdraft occurs when a fire has consumed most of the available oxygen and is in a smoldering state. If fresh air is suddenly introduced into that oxygen-depleted environment, it can lead to a rapid re-ignition and explosive fire behavior. This is due to the sudden increase in available oxygen, which can cause the existing combustible gases to ignite almost instantaneously, resulting in an explosive reaction.

Understanding the dynamics of fire behavior is crucial for fire fighters, as recognizing the signs of a backdraft—such as smoke being pushed out of openings or a dark, turbulent plume—can help in taking the necessary precautions to prevent it. Proper training and awareness of backdrafts are vital for safety during firefighting operations, especially in confined spaces with limited airflow.