Which phase of burning is characterized by a rapid increase in fire intensity?

The phase of burning that is characterized by a rapid increase in fire intensity is the free-burning phase. During this stage, the fire reaches its maximum potential, with a significant amount of fuel being consumed rapidly. The increase in heat release and flame production is pronounced, leading to a robust and dynamic fire behavior.

In this phase, the fire can spread quickly due to sufficient oxygen supply and the availability of combustible materials. This contrasts with other phases, such as the incipient phase, where the fire is just beginning and lacks intensity, or the smoldering phase, which follows a decrease in available fuel and oxygen, leading to a lower intensity fire. The cooling phase represents the period when the fire's heat begins to dissipate, marking a significant decrease in intensity.

Understanding these phases is crucial for effective fire response and management, allowing security personnel to gauge fire behavior and take appropriate action.