Define flashover.

• A. A sudden collapse of a structure due to failure of a beam.
• B. The rapid transition to near-simultaneous ignition of all combustibles in a room due to extreme heat.
• C. A temporary cooling of hot gases by ventilation.
• D. A slow burn of contents.

Answer: (B)

Flashover is the rapid transition where the heat in a room becomes high enough that nearly all combustibles ignite almost simultaneously. This happens when radiant heat from the flames and the hot, rising gases raise the surfaces and contents to their ignition temperatures, so within seconds everything that can burn ignites. It marks a dramatic shift from a localized fire to a fully developed, room-ignited environment, with temperatures typically in the hundreds of Celsius (roughly 500–600°C or about 900–1100°F). This event creates extremely high heat flux and a sudden, dangerous spread of fire, drastically increasing danger to anyone inside or nearby. It’s different from a cooling or ventilation-driven effect, and from a gradual burn; flashover is the explosive ignition of most contents in a space.