What is rollover?

What is rollover?

• A. The spontaneous ignition of hot gases at the upper level of a room
• B. The spread of flames across a floor
• C. The cooling of a compartment due to ventilation
• D. The detonation of gas pockets at floor level

Answer: (A)

Rollover is the ignition of the hot, combustible gas layer that forms up near the ceiling as a fire grows. The hot combustion products rise and collect at the top of the room, creating a flammable layer. If that upper layer reaches its ignition temperature and an ignition source is present, the entire ceiling layer can ignite, making flames roll across the ceiling. This is a warning sign that the fire has progressed toward a rapid, dangerous phase and could lead to flashover if not controlled.

That aligns with the described option because it specifically describes ignition occurring in the upper gas layer, not at the floor. The idea of flames spreading across the floor describes a different mode of spread, cooling due to ventilation isn’t about ignition of gases, and a detonation of gas pockets at floor level is a separate explosive phenomenon rather than ceiling-layer ignition.