A pre-mixed pocket of fire gases that ignites when it comes into contact with an ignition source describes which phenomenon?

• A. Backdraft
• B. Flashover
• C. Incipient Stage
• D. Decay Stage

Answer: (A)

Backdraft happens when a confined space fills with hot, fuel-rich fire gases that have built up from the fire consuming oxygen. When air finally enters or an ignition source is introduced, that accumulated gas-air mixture ignites violently, producing a sudden flame burst and pressure surge. The key here is the presence of a pre-mixed, combustible gas mixture inside the space, which ignites rapidly once exposed to oxygen or an ignition source. This differs from flashover, where heat raises the entire room to ignition temperature and nearly simultaneous ignition of all surfaces occurs. The incipient stage is the initial growth of the fire, not a gas pocket ignition, and the decay stage is when the fire is waning.