What is the term used to describe the condition where unburned fire gases accumulate at the top of a compartment and ignite?

The condition described in the question is typically referred to as rollover. Rollover occurs when unburned fire gases, which have accumulated at the upper part of a compartment, reach their ignition temperature and ignite, creating a visible flame front. This phenomenon is an important indicator during a fire situation, as it signals that the environment is reaching a critical state and that the fire could rapidly intensify.

Recognizing rollover is crucial for firefighting operations because it helps firefighters understand the fire dynamics at play, allowing them to adjust their tactics accordingly to enhance safety and effectiveness. It is an observable event that can provide critical information about the state of the fire and should be monitored closely.

The other terms refer to different fire phenomena: backdraft involves an explosive ignition of accumulated flammable gases when fresh air is introduced, flashover is a rapid spread of fire when a combustible area reaches its ignition temperature, and smoke layer simply refers to the accumulation of smoke and gases in a space, but does not specifically relate to ignition.