Which fire behavior is characterized by a rapid increase in heat and the sudden onset of fire?

The phenomenon characterized by a rapid increase in heat and the sudden onset of fire is known as flashover. This occurs when the temperature in a room rises to the point where combustible materials reach their ignition temperature almost simultaneously, resulting in a fire that can engulf the entire area almost instantaneously. Flashover is a critical stage in a fire's development, as it signifies that the situation has escalated to a particularly dangerous level, with extreme heat and rapidly spreading flames.

Understanding flashover is crucial for firefighters, as recognizing the signs and conditions leading up to it can significantly impact safety and tactical decisions. Key indicators often include a buildup of heat, the presence of smoke, and the absence of visible flames until flashover occurs. In contrast, flame spread involves the movement of fire on a material's surface, backdraft refers to an explosive event caused by the introduction of air into a smoldering fire, and smoldering itself is a slow, low-temperature form of combustion that lacks the rapidity and intensity seen in flashover.