In which phase of fire does the fire plume start to draw air from its surroundings?

The phase during which the fire plume begins to draw air from its surroundings is the growth or free burning phase. In this phase, the fire has gained enough energy and heat to create a significant temperature difference between the hot gases produced by the fire and the cooler air outside of the fire. This temperature difference creates a convective current that draws in fresh air to sustain combustion.

As the fire continues to burn, it will increase in intensity. The fire plume becomes a dominant force in pulling in air from the environment, feeding the flames and allowing the fire to grow in size and temperature. This behavior is crucial for understanding how fires spread and can inform tactics for containment and control.

In contrast, the ignition phase is primarily focused on the initial stages of combustion, where the fire is just starting and has not yet developed enough energy to draw significant amounts of air. The fully developed phase refers to a point where the fire has reached its maximum growth and is, in essence, stable but may not be actively drawing in more air as efficiently as during the growth phase. Lastly, the decay phase indicates a reduction in available fuel and heat, leading to the fire losing intensity and eventually extinguishing, which is the opposite of drawing in more air.