Handline can be relied upon to hold a fire only if the flame lengths are:

The correct response is based on the principle of fire behavior and the effectiveness of handline fire suppression methods. Handlines, which are hoses used by firefighters to apply water or foam directly on fires, can effectively manage flames up to a specific height. When flame lengths are less than 4 feet, firefighters can maintain better control and apply water efficiently, minimizing the risk of fire escape and enhancing the effectiveness of their suppression efforts.

As flame lengths increase, the fire's intensity and heat also increase, making it more challenging for firefighters to extinguish the flames without risking inadequate suppression or the potential for flashover. Therefore, the guideline that handlines are reliable for controlling flames that are less than 4 feet tall is critical for ensuring safety and effectiveness in wildland firefighting operations. This guideline helps firefighters make strategic decisions regarding when to use handlines versus needing additional resources or tactics for larger fire behaviors.