Which of the following is a characteristic of master stream devices?

• A. Multiple Large-Diameter Hose (LDH) supply lines are required.
• B. They cannot flow as much water as hand lines inside the structure.
• C. The person operating the device must be certified to at least the firefighter II level.
• D. They deliver a large volume of water that can increase the chance of structural collapse.

Answer: (D)

Master stream devices are built to deliver a large volume of water quickly, creating a powerful stream that can rapidly knock down a fire and cool exposed areas from an exterior position. This high flow is their defining strength, allowing firefighters to control large, demanding fires and protect interior crews by pushing the fire toward a safer progression of operations.

But that same high volume and force can place substantial stress on a structure, especially if the building is already compromised. The intense water application can contribute to structural strain, glazing, floor and wall failures, or progressive collapse if used inappropriately or without adequate caution and coordination. That is why the characteristic most associated with master streams is the ability to deliver a large amount of water, with an accompanying risk of structural effects if not managed carefully.

The other statements aren’t defining traits. Supplying with multiple LDH lines isn’t mandatory, and master streams can be fed in different ways depending on the scene. They can discharge more water than hand lines, not less, and the operator’s certification level, while important for overall safety, isn’t what defines the device itself.