Which of the following is considered a precursor to potential flashover?

• A. Free burning
• B. High temperatures
• C. Heavy dark smoke
• D. Rollover

Answer: (D)

Rollover is the moment when the hot gases pooled at the ceiling ignite and begin moving flames across the upper layer, signaling that the fire is near a rapid transition to full room involvement. Seeing flames roll over the ceiling shows the gas layer has reached ignition temperature and is mixing with air, which is a strong warning that flashover could occur imminently. This specific upper-layer ignition is what makes rollover a clear precursor to potential flashover.

Other signs indicate fire growth or conditions, but they don’t pinpoint the imminent transition as directly. Free burning describes flames spreading through available fuels, which is part of normal growth but not a specific warning of an impending flashover. High temperatures show heat present but aren’t in themselves a standalone precursor. Heavy, dark smoke reveals abundant fuel in the gases and ongoing combustion, yet rollover specifically demonstrates the ignition of the ceiling gases that can precede flashover.