Flashover is defined as which event?

• A. Simultaneous ignition of contents in a room.
• B. Ignition of accumulated gases when air is introduced.
• C. Structural collapse due to heat.
• D. Smoke layering without ignition.

Answer: (A)

Flashover is the moment in a room fire when the heat has built up enough that the contents of the room ignite nearly at the same time, causing the space to become fully involved in flames. The key idea is the rapid, near-simultaneous ignition of all combustibles due to intense heat and heat radiation reaching their ignition temperatures throughout the room. This is what makes flashover so deadly: a fire that starts in one area can suddenly spread to everything in the space in a matter of seconds.

This differs from a backdraft, where accumulated flammable gases ignite when air is suddenly introduced, often with an explosive release. It also isn’t about smoke layering without ignition or about structural collapse from heat, which are separate fire phenomena.