What is the cause of a backdraft?

A backdraft occurs when there is a sudden introduction of oxygen into a closed, heated space that contains unburned fuel and hot gases. In a situation where a fire has been smoldering, the combustion process can consume most of the available oxygen, causing the fire to diminish or become nearly extinguished. When a door or window is opened, or if some other means of introducing fresh air is provided, a rush of oxygen can ignite the trapped flammable gases and smoke that have built up, resulting in a rapid and explosive combustion event.

The other options do not lead to a backdraft. Introducing water into a hot fire may create steam but does not directly provoke a backdraft scenario. Excessive smoke in a confined area indicates incomplete combustion but does not inherently lead to the conditions necessary for a backdraft. Lastly, heat dissipating away from the fuel source is not a catalyst for backdraft; in fact, it is the lack of oxygen that contributes to the suppression of fire.