What type of stream is preferred when quick knockdown is required?

A straight stream is the preferred choice when quick knockdown of a fire is required because it delivers water in a focused and powerful manner. This concentrated stream of water allows firefighters to effectively penetrate the flames and reach the heat at the base of the fire, where it can be most efficiently extinguished. The straight stream minimizes the chances of steam generation in the early stages of an attack, allowing for better visibility and a more direct application of water to the fire.

In contrast, while a fog stream can provide a wider coverage area and helps to cool the fire's environment, it may not be as effective for immediate knockdown of flames due to the dispersal of water droplets. Master streams are typically used for larger fires or when dealing with high-volume water delivery is necessary, which may not facilitate a rapid knockdown of small or localized fires. A spray stream is generally less effective for structural fires because of its wide distribution and lower water application rate, further delaying effective extinguishment.

Therefore, the straight stream is the most effective method for achieving quick knockdown when faced with a fire scenario.