Which statement best describes backdraft?

• A. A rapid cooling of hot gases when air is introduced
• B. A sudden ignition of accumulated flammable gases when air enters a closed space; signs include high heat, dense smoke, and a visible change when openings are made
• C. A steady flame front with consistent smoke
• D. A loud explosion with no smoke

Answer: (B)

Backdraft happens when a compartment containing a fire has become filled with hot, flammable gases but has limited or no available oxygen. When air is suddenly introduced—such as by opening a door or breaking a window—that gas-air mixture ignites violently, producing a rapid ignition or explosion. The described signs—very high heat, dense smoke, and an abrupt change when openings are made—fit this phenomenon, because the incoming air creates the right fuel-air mixture and the heat pushes the ignition reaction instantly.

This differs from a steady flame or smoke pattern, which would indicate a normal, ongoing fire rather than a sudden explosive ignition of trapped gases. It also isn’t simply a loud explosion with no smoke, which wouldn’t capture the typical heavy smoke and rapid ignition dynamics of a backdraft.