What is the term for ignition occurring at the underside of the hot gas layer?

The term for ignition occurring at the underside of the hot gas layer is known as flameover or rollover. This phenomenon occurs when combustible gases that have accumulated in a hot gas layer become ignited, leading to a rapid spreading flame that travels along the interface between the hot gas layer and cooler air. During this event, unburned gases that have reached their ignition temperature will ignite, creating a visible flame that may appear to be rolling across the ceiling or upper section of the room.

Understanding this process is crucial for fire investigators and firefighters, as it indicates the potential for rapid fire growth and the need for immediate safety measures. Flameover or rollover is especially dangerous in enclosed spaces, as it can result in sudden and uncontrolled fire behavior. Recognizing the signs of this phenomenon can help in assessing the scene and implementing appropriate strategies for attack or evacuation.

The other terms refer to different fire behavior phenomena: explosive ignition pertains to an instantaneous ignition that results from rapid heat buildup, backdraft refers to a fire behavior phenomenon where a sudden influx of oxygen ignites combustible gases in a fully involved fire, and burning out describes a stage of fire where fuel has been fully consumed and the flames are extinguishing. Each of these concepts is important in the context of fire dynamics