During an indirect attack, water should be flowed until the:

In the context of an indirect attack in firefighting, the objective is to cool the environment and reduce the temperature within a structure before making entry. This approach helps to create safer conditions for both firefighters and potential victims.

Flowing water until the room begins to darken indicates that the effectiveness of the cooling process is taking place. As the water vaporizes, it absorbs heat; this can lead to a change in the smoke conditions. The darkening effect happens when the steam generated from the water contact with hot gases begins to saturate the environment, indicating that the fire is being effectively attacked from a safe distance.

This stage is crucial as it implies that the hot gases are cooling down and that conditions may be improving, making it potentially safer for firefighters to enter the room for direct attack or to search for victims. This tactical strategy is aimed at controlling the fire from outside the immediate fire zone before making a direct approach.