During which stage does the fire plume develop and begin to entrain air?

The growth stage of a fire is when the fire plume develops and starts to entrain air. During this stage, the increased heat release from the combustion process causes the gases produced by the fire to rise, creating a plume. As the plume ascends, it draws in surrounding cooler air, a process known as entrainment. This interaction of the hot gases with the cooler air helps to sustain and intensify the fire and can lead to more rapid fire spread if enough oxygen is mixed into the combustion zone.

In contrast, the ignition stage refers to the point at which the fire is first initiated, which does not involve a developed plume or significant air entrainment. The fully developed stage indicates that the fire has reached maximum growth and is burning steadily, but it is not the stage where the plume first begins to form. The decay stage occurs when the fire starts to diminish as fuel is exhausted, signifying a reduction in both heat output and plume activity. Therefore, the growth stage is the critical period for plume development and air entrainment.