Which statement best describes the relationship between confinement of the air/fuel mixture and backdraft severity?

• A. The more confined the air/fuel mixture, the more violent the backdraft.
• B. The more dispersed the air/fuel mixture, the more violent the backdraft.
• C. The more confined the air/fuel mixture, the less violent the backdraft.
• D. The more starved the air/fuel mixture, the more violent the backdraft.

Answer: (A)

The severity of a backdraft hinges on how confined the fuel-rich gases are before ignition. When the air/fuel mixture is tightly confined in a closed or poorly ventilated space, a large amount of unburned fuel vapors and heat are trapped in a small volume. Open a path for air and those gases mix with oxygen in a sudden, rapid way, reaching flammable concentrations and producing an explosive, highly violent ignition. If the mixture is more dispersed, the fuel is diluted, the energy release is spread out, and the ignition is less dramatic. Starving or diluting the mixture reduces the potential for a violent backdraft because there’s less fuel and heat to drive a rapid explosion.