Backdraft is a sudden, explosive ignition of hot, fuel-rich gases that have built up in an enclosed space when fresh air (oxygen) suddenly enters. It can send a blast of flame and smoke out of an opening and is a major danger to anyone nearby, especially firefighters, because the rapid combustion can be violently forceful and unpredictable. Key points

• What it is: A rapid combustion of accumulated flammable gases in a confined space once oxygen levels spike, typically after a door or window is opened or a ventilation opening is created. This sudden influx of air mixes with hot, fuel-rich gases and can ignite almost instantaneously.
• Why it’s dangerous: The ignition is often more violent than the visible fire inside the room, producing a pressure wave that can throw objects, cause structural loads to shift, and injure or kill nearby personnel. The explosion can occur without warning, even if the visible flames have subsided, because the buildup of gases may be hidden behind walls or ceilings.
• When it happens: In many indoor fires where a space becomes starved of oxygen, heat and unburned gases accumulate. Opening a door, breaking a window, or adding ventilation can introduce the oxygen that triggers the backdraft.
• Related concepts: Backdraft is sometimes discussed alongside flashover, but they are distinct phenomena. Flashover refers to a near-simultaneous ignition of everything in a room when it reaches a critical temperature, whereas backdraft is specifically triggered by a sudden air influx into a gas-rich, oxygen-depleted environment.

Safety implications and prevention

• Firefighters risk assessment uses signs like dense, smoky, stratified layers, rollover of flames, or a closed door with heavy heat behind it to anticipate backdraft. Ventilation strategies are carefully planned to avoid uncontrolled air entry; controlled ventilation and continuous monitoring are essential.
• In non-professional settings, avoiding actions that force air into a hot, enclosed space and alerting authorities to a suspected backdraft risk are prudent steps.

If you’d like, I can tailor this to a specific scenario (e.g., residential fire, industrial facility) and add signs to watch for, plus recommended response steps.