backdraft

Backdraft is a dangerous rapid ignition phenomenon that occurs in enclosed spaces when a ventilation-limited fire accumulates a flammable, fuel-rich gas mixture. The term refers to an explosive ignition of this gas when fresh air enters the space, typically through a door or window.

In a burning room, the fire consumes available oxygen and produces hot gases and smoke. If the room becomes sealed or poorly vented, the fire can continue to generate fuel-rich vapors and radiant heat while oxygen is depleted. When a new supply of air reaches the gas-laden layer near the opening, the mixture can ignite abruptly, producing a flame front and a blast that may blow the opening apart.

Common signs include heavy smoke buildup and high heat with little visible flame, smoke that blankets the ceiling, a sudden draft or rush of air when a door is opened, and a popping or hissing sound as gases mix with air.

Backdraft differs from flashover, in which heat causes simultaneous ignition of all combustibles in a room; backdraft specifically involves ignition of accumulated gases due to renewed oxygen.

Safety considerations emphasize recognizing the signs of a possible backdraft, using controlled ventilation, and cooling the space to reduce temperatures and gas concentrations before interior entry. In firefighting practice, trained personnel employ specific tactics to minimize the risk, including delaying near-doors openings and using protective equipment.