What condition occurs when oxygen is admitted into an area filled with unburned carbon particles and fire gases?

The condition described in the question relates specifically to backdraft. A backdraft occurs when there is a sudden influx of oxygen into a space that is filled with unburned carbon particles and flammable fire gases, typically after a period of smoldering. This condition can lead to an explosive ignition if the oxygen introduced reaches the fuel in a sufficiently concentrated manner, resulting in a rapid fire development.

Unlike the other options, backdraft shows a unique interaction between oxygen and unburned gases that have accumulated in a confined environment, where an initial fire has been starved of oxygen and is not actively burning. The introduction of air into this environment can create highly dangerous conditions due to the volatile mixture of heat, fuel, and suddenly available oxygen, producing a violent re-ignition.

The other choices refer to different phenomena: flashover describes a rapid spread of fire through combustion of all exposed surfaces in a room, flameover is a term often used for a brief flare-up of flames over a fire, and smoke explosion refers to an explosion caused by the ignition of smoke particles. Each of these phenomena involves combustive reactions but does not specifically capture the principle of oxygen interacting with unburned fuel and smoke as backdraft does.