What is flashover in a compartment fire?

• A. Backdraft scenario occurs when fresh air is introduced into an oxygen-depleted, fuel-rich space.
• B. A temporary ignition of a gas layer near the ceiling due to stratified heat.
• C. Rapid ignition of all combustibles in a room due to heat buildup, typically when the fire becomes fully developed and temperatures reach the fuels' ignition point.
• D. A flame front traveling along a single fuel source.

Answer: (C)

Flashover is the rapid, nearly simultaneous ignition of the major combustibles in a room brought on by heat buildup as the fire progresses. As temperatures rise, surfaces and contents heat to the point where fuels begin to pyrolyze and release flammable gases; when those gases and other fuels reach their ignition temperature, they ignite almost at once, causing the entire room to become involved in flames. This marks the shift to a fully developed, quickly spreading fire and is incredibly dangerous for anyone inside or nearby.

Backdraft describes a different scenario: ignition of accumulated fuels when fresh air suddenly rushes in, not a room-wide simultaneous ignition. Ignition of a gas layer near the ceiling is a localized layer ignition, not the whole space. A flame front moving along a single fuel source is just fire traveling along one fuel path, not the global room involvement characteristic of flashover.