The use of master streams on a building should be prohibited when?

The use of master streams on a building should be prohibited when crews are actively working inside to ensure the safety of all personnel involved in the firefighting efforts. Master streams, such as those from aerial devices or large handlines, deliver a significant volume of water and are designed to quickly suppress fire over a large area. However, if firefighters are inside the structure, particularly in close proximity to the fire, the application of a master stream can create hazardous conditions.

The pressure and volume of the water could potentially cause structural instability or shift burning materials, leading to falling debris. Additionally, the water can displace smoke and heat, which can be dangerous for crews who are trying to assess and control the fire. Therefore, using master streams while crews are inside creates a serious risk of injury or death, underscoring the critical importance of maintaining safe operational practices during firefighting.

Other scenarios like contained fires, low visibility, or limited water supply may influence tactics, but the immediate risk to personnel working within the structure makes that the priority consideration.