Flashover is best defined as what phenomenon?

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

Answer: (B)

Flashover is the rapid, nearly simultaneous ignition of all combustible materials in a confined space, causing the room to become fully involved in flames. As heat builds in a compartment, surfaces and contents reach their ignition temperatures and the fire shifts from burning in a localized area to a condition where the entire room ignites at once. The hot gases layer and radiate heat to other fuels, so once ignition happens across exposed fuels, the entire space bursts into flames.

This is distinct from backdraft, which is an explosive ignition when a vent is opened to a fuel-rich, smoldering space and fresh air suddenly mixes with hot gases. A neutral plane refers to the vertical boundary between layers of air and combustion products, not an ignition event. A smoke explosion involves rapid ignition of accumulated smoke and unburned gases, but not the whole room’s contents igniting at once like flashover.