What term describes a condition where flames move through or across unburned gases during a fire's progression?

The term that accurately describes the condition where flames move through or across unburned gases during a fire's progression is flameover. This phenomenon occurs when the flames ignite the available unburned fuel gas that is present in the atmosphere, resulting in a rapid movement of fire across the surface of these gases.

Flameover typically happens when the heat from the fire raises the temperature of the unburned gases to their ignition point. The flames can travel horizontally, creating a dangerous situation because this can lead to a rapid increase in fire intensity and spread. Understanding this concept is crucial for firefighters as it helps them anticipate and recognize potentially hazardous conditions during fire suppression efforts.

In contrast, flashover refers to the rapid spread of fire throughout a space, caused by the simultaneous ignition of combustible materials due to extreme heat, while backdraft involves an explosive combustion that occurs when a fire is smoldering and is suddenly exposed to oxygen. A firestorm refers to an intense and widespread fire phenomenon, commonly associated with wildfires or large urban conflagrations, but does not specifically describe the interaction of flames with unburned gases in the same manner.