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 working inside the building due to the potential danger posed to firefighters. Master streams are high-volume water flow devices used to combat fires, and their application can generate significant water pressure and volume. This can create hazardous conditions, such as the possibility of structural collapse or the dislodging of critical fire suppression barriers that could protect firefighters inside. The intense water flow could also impede visibility, disrupt search and rescue operations, or create additional risks of injury to personnel engaged in firefighting efforts within the structure.

In scenarios where crews are inside the building, it is vital to maintain their safety and ensure clear communication and coordinated efforts. Using master streams while these teams are operating can complicate situations and endanger lives. Therefore, deploying such high-capacity streams is typically avoided until all personnel have safely evacuated the building or until the operational command determines it to be the only safe option available without jeopardizing those inside.