Isolated flames moving throughout the hot gas layer of a growing fire is sometimes an immediate indicator of

• A. Flashover.
• B. Backdraft.
• C. Convention.
• D. Smoke explosion.

Answer: (A)

The situation described points to rollover, which signals flashover. In a growing room fire, hot gases collect near the ceiling. When those gases reach ignition temperature and ignite, flames can roll or spread along the ceiling—flames appearing to move within the hot gas layer. This rollover is a clear, dangerous sign that the fire is transitioning into flashover, where the contents of the space can ignite rapidly and almost simultaneously. Backdraft involves a sudden ignition when air is suddenly drawn into a highly ventilated, fuel-rich space, not flames moving within the hot gas layer. Convection is a heat transfer mechanism, not an immediate fire behavior indicator like rollover. A smoke explosion is a separate phenomenon involving explosive ignition of smoke and fuel in air, not the ceiling-layer rollover sign. So, the best answer is flashover, with rollover being the visible precursor indicating that transition.