Which factor directly affects friction loss in a fire hose?

• A. Ambient temperature
• B. Atmospheric pressure
• C. Water source
• D. Hose diameter

Answer: (D)

Friction loss in a fire hose is driven by how water interacts with the hose interior, which is primarily controlled by the hose’s internal diameter. When the diameter is smaller, water must move faster to deliver the same flow, increasing wall friction and turbulence and causing greater energy loss per foot of hose. Conversely, a larger diameter reduces the velocity for the same flow and significantly lowers friction loss along the length. This is why choosing a larger hose diameter is a direct and powerful way to limit pressure loss when pumping water over distance. Ambient temperature, atmospheric pressure, or the water source can affect other aspects of the system, but they don’t govern friction loss along the hose as directly as the hose diameter.