What is the purpose of wye lines in firefighting?

The purpose of wye lines in firefighting is to effectively split a larger diameter hose into two smaller diameter hoses, which allows for multiple lines to be operated simultaneously from a single source of water. In practical terms, when a 2.5" hose is used, it can be connected to a wye fitting that divides the flow into two 1.75" hoses. This arrangement is beneficial during firefighting operations, as it enables firefighters to provide more concentrated streams of water at different locations, thereby increasing the efficiency of their attack on a fire.

This configuration is especially useful in scenarios where space is confined, or when an initial attack strategy requires multiple lines to be deployed quickly from one water source. By using a wye, fire crews can better coordinate the firefighting effort while optimizing water usage without needing to pull additional large hoses.