What state of combustion occurs when sufficient oxygen is present for open burning?

The free burning state is characterized by a situation in which there is adequate oxygen available to support combustion, allowing flames to burn steadily and actively. In this phase, the fire can spread effectively, fueled by the available oxygen and combustible materials in the environment. This stage is typically marked by visible flames and a high rate of heat release. With sufficient oxygen, the fire can continue to sustain itself and grow, leading to a more intense and prolonged burn.

In contrast, flashover is a rapid transition from the free burning state to a state where all combustible materials in a room ignite almost simultaneously, which requires specific conditions that go beyond mere open burning. Backdraft, on the other hand, occurs when a fire is burning in a confined space with limited oxygen, and the introduction of fresh air causes a rapid combustion event. The burning brand test is a method used to evaluate the ignitability of materials through controlled ignition processes, rather than a state of combustion. These distinctions highlight why the free burning state is the correct answer in the context of open burning with sufficient oxygen present.