Which of the following scenarios may indicate a flashover is imminent?

The scenarios listed all serve as significant indicators that a flashover may be imminent.

Flame rollover occurs when flames propagate along the ceiling or the upper layer of smoke, showing that the fire is gaining in intensity and that the environment is becoming increasingly dangerous. When flames start to roll over towards the ceiling, it indicates that the hot gases above the flames are heating to an extent that can lead to a flashover.

High heat detected near the ceiling is another critical sign. The ceiling area can become an accumulation space for heat and gases released from the burning materials. If thermal readings show extreme heat concentrations near the ceiling, it signals that the environment is close to reaching the flashpoint for an explosive fire spread.

Smoke thickening and darkening is also a key indicator. As a fire grows, the smoke produced becomes denser and darker due to incomplete combustion. This thickening and darkening smoke signifies that there is a significant amount of heat and flammable gases present, which can contribute to flashover conditions.

Considering all these elements together, selecting the option that indicates all of the above scenarios as predictors of imminent flashover provides a comprehensive understanding of the behaviors associated with fire progression and the dangers firefighters face in such situations.