What is meant by entrainment in the context of fire science?

Entrainment refers specifically to the process in which air or combustion gases are drawn into a fire, plume, or jet. This phenomenon plays a critical role in how fires behave and propagate. When air is entrained into a flame, it mixes with the combustibles, which can enhance the fire's intensity and alter its propagation characteristics. Understanding this process is vital for fire science as it influences combustion efficiency, flame stability, and overall fire dynamics.

Other options describe different concepts related to fire dynamics but do not align with the precise definition of entrainment. The mixing of fuel and air is an intrinsic part of combustion but doesn’t specifically encapsulate the air-influence aspect of entrainment. The introduction of water to control fire is a firefighting strategy, not a concept pertinent to how air interacts with flames. The expansion of fire due to increased temperature is a physical phenomenon related to heat but doesn't capture the essence of how air is integrated into a fire since it doesn’t directly involve the influx of air or gases.