The use of master streams on a building should be prohibited if __________.

The correct answer is that the use of master streams on a building should be prohibited if crews are working inside the building. This is because master streams involve high-volume water application, which can drastically change the conditions within a structure. If firefighters are operating inside, the powerful force of the water could create a risk of disorientation, injury, or complications in their operations. It may also potentially collapse walls or ceilings that are already weakened by fire. Ensuring the safety of crews is paramount; therefore, when personnel are inside a building, caution dictates that streaming high volumes of water should be avoided.

While risks associated with structural collapse, poor weather conditions, and the fire being fully involved are significant factors to consider in firefighting operations, the greatest immediate safety concern revolves around the personnel actively working within the structure.