What phenomenon occurs when oxygen is introduced into a compartment with flammable gases?

The introduction of oxygen into a compartment that contains flammable gases can lead to a phenomenon known as backdraft. A backdraft occurs when there is a sudden influx of oxygen into an area that is already filled with unburned gases, which can ignite explosively due to the high concentration of flammable vapors and the rapid increase in available oxygen.

In situations where a fire has consumed most of the available oxygen, the remaining flammable gases can accumulate; they do not ignite right away due to the lack of oxygen. When windows or doors are opened, or if other ventilation occurs, oxygen enters the space. This sudden addition can create the right conditions for an explosive ignition—resulting in flames and pressure waves that can be very dangerous to firefighters and anyone nearby. The rapid combustion of the accumulated gases leads to the characteristic violent burst of fire associated with backdrafts.

Other available options represent different fire phenomena. Flashover is characterized by the rapid spread of fire throughout a room and not necessarily linked to the sudden introduction of oxygen. Smoke explosions occur when smoke ignites, often as it escapes an enclosed area, and combustion describes the general chemical reaction of burning but does not specify the unique conditions of oxygen introduction leading to a backdraft.