What can result from a sudden introduction of air into an oxygen-depleted space?

• A. Flashover
• B. Backdraft
• C. Explosive decompression
• D. Smoke explosion

Answer: (B)

Backdraft happens when a fire in a confined space uses up the oxygen and the products of pyrolysis—hot, flammable gases—build up without enough oxygen to burn. When a door or window is suddenly opened and fresh air rushes in, the oxygen mixes with those hot gases and they ignite explosively, creating a rapid flame burst and pressure spike. This is the classic danger of introducing air into an oxygen-depleted area.

Flashover, by contrast, is a heat-driven event where nearly all combustibles in a room ignite as the temperatures rise, not primarily caused by a sudden air influx. Explosive decompression describes a rapid pressure drop from venting or rupture, not ignition of gases. Smoke explosion refers to ignition of smoke gases when air re-enters, but the defining feature tied to an oxygen-depleted space and sudden air entry is backdraft.