A condition that occurs when flames move through or across unburned gases during a fire's progression is known as what?

The condition described in the question is known as rollover. During a fire, as the flames consume burning materials and heat the gases that rise above, there can be a moment when these unburned gases reach their ignition temperature. When this occurs, the flames can travel across or through these gases, causing a phenomenon known as rollover. It typically manifests as a rolling motion of flames across the ceiling or upper layers of a space, indicating the presence of unburned fuel in the form of superheated gases.

Understanding rollover is crucial for firefighters because it alerts them to the potential of increased fire intensity and rapid flame spread, which can create dangerous conditions. Rollover can occur just before a flashover, which is an even more severe condition where all combustible materials in the room ignite almost simultaneously. The distinction between rollover and flashover is essential for effective fire suppression strategies and safety measures in firefighting operations.