The explosion of accumulated fire gases generally caused by admitting air into a superheated environment is known as which phenomenon?

• A. Backdraft
• B. Neutral Plane
• C. Smoke Explosion
• D. Flashover

Answer: (D)

Backdraft is the phenomenon described when air enters a superheated, oxygen-starved space and the accumulated fire gases ignite explosively. In a confined fire, fuels decompose and gasify, building up a dense, hot layer of combustible gases. When fresh air is suddenly admitted—through a doorway, window, or vent—these gases mix with oxygen and can ignite violently, producing an explosive burst and a pressure spike. This is why backdraft is often associated with a dangerous “air entering a sealed space” scenario and a rapid, explosive flame front.

This differs from flashover, which is a heat-driven event where radiant heat raises temperatures enough that all fuels in the room ignite almost simultaneously, but not as a gas explosion from entering air. It also differs from a smoke explosion, which involves ignition within the smoke layer itself, and from the neutral plane, which is a ventilation/pressure concept rather than a gas-explosion phenomenon.

So, the event described is backdraft. Signs to look for include heavy, stagnant smoke, a lack of visible flame, a very hot environment, and a sudden surge of air or a brief explosive burst when openings are created.