Which factor is included in the friction loss calculation for hydraulic performance?

• A. Ambient temperature only.
• B. Hydraulic color of water.
• C. The hose size, the flow, the length, and fittings losses.
• D. The phase of the moon.

Answer: (D)

Friction loss is the pressure drop caused by resistance to flow inside the hose and through fittings. The factors that determine this loss are the hose diameter, the amount of water moving (flow), the distance the water travels (length), and the additional losses caused by fittings such as elbows and adapters. A smaller diameter increases resistance for the same flow, raising friction loss; higher flow means higher velocity and more turbulence, which increases losses; longer hose adds more length of resistance; and each fitting adds its own additional loss, usually represented as a K factor converted to a head loss. In typical firefighting calculations, we use standard water conditions, so ambient temperature isn’t treated as a separate factor in the basic friction loss formula, though water viscosity does change with temperature in precise calculations. The color of the water and the phase of the moon don’t affect friction loss.