Which term describes the process of hot gases rising and pooling near the ceiling?

• A. Rollover
• B. Flashover
• C. Backdraft
• D. Ignition

Answer: (A)

Hot gases rise because they are lighter than the surrounding air, forming a hot, gaseous layer that pools near the ceiling. When this ceiling-layer of hot gases and vapors reaches ignition conditions, the flames can sweep across the ceiling in a rolling front—the rollover phenomenon. This describes the movement and ignition of the upper gas layer, which is why it’s the best match for the scenario.

Flashover is when heat becomes so intense that all fuels in the room ignite almost simultaneously. Backdraft is a sudden explosion caused by a rapid influx of air into a confined space with accumulated, smoldering fuels. Ignition is simply the general act of something catching fire, not specifically about the ceiling-level gas behavior.