During an indirect attack, you should flow water until the:

In an indirect attack, the objective is to cool the fire from a safe distance, often using a hose line to direct water into the upper levels of a structure where heat and smoke tend to accumulate. The correct answer indicates that the room should begin to darken, meaning that water vapor is condensing and reducing the amount of heat and smoke present in the atmosphere.

This darkening effect indicates that the water is effectively cooling the fire gases, which in turn can help lower the temperature in the room and potentially extinguish the fire. By achieving this, firefighters can create conditions that make it safer for them to enter the room and perform additional firefighting or rescue operations.

The indication of darkening occurs when the thermal energy in the room is significantly reduced, signaling success in controlling the fire's environment. This process is crucial in preparing for a direct attack while minimizing the risk of re-ignition or backdraft when entering the space. The other potential scenarios, such as smoke levels reaching the floor or clearing of the atmosphere, do not necessarily signify that the cooling effect is occurring effectively, and they could lead to hazardous conditions if the firefighter proceeds prematurely.