What characteristic defines a backdraft event?

A backdraft event is characterized by an explosive ignition that occurs when a significant amount of oxygen is suddenly introduced into an environment that has been starved of oxygen while fire-related gases are accumulating. In a backdraft scenario, a fire that has been burning in a confined space may produce combustible gases, such as carbon monoxide and unburned hydrocarbons, which can rapidly accumulate to dangerous levels. When the firefighter or rescuer opens a door, window, or some other opening, oxygen enters the space, resulting in a sudden and violent ignition of these gases. This explosive reaction can put lives at risk and cause extensive damage to the structure and surroundings.

When considering the other options, the concept of a sudden extinguishment of fire does not align with backdraft characteristics, and smoldering fires, while they have their own hazards, do not involve the explosive potential indicative of a backdraft. Lastly, a complete lack of flammable materials would inherently prevent any fire from occurring in the first place, making it irrelevant to the definition of a backdraft.