How is friction loss in a standpipe or attack hose calculated and applied on scene?

• A. Ignore friction loss and set pump discharge pressure to a fixed value.
• B. Multiply nozzle pressure by hose length and ignore other factors.
• C. Use standard friction loss charts for hose size and flow, add entrance and nozzle pressure; ensure pump discharge pressure meets needed GPM.
• D. Use friction loss only for vertical lift calculations.

Answer: (C)

Friction loss is the pressure drop that occurs as water moves through hose and fittings, and on scene you must calculate it to deliver the correct water flow to the nozzle. The way to do this reliably is by using standard friction loss charts that relate hose size and flow (GPM) to a psi loss per 100 feet. You take the actual hose length, multiply the chart’s psi-per-100 ft by the length in hundreds of feet to get the total friction loss for that run. Then you add the nozzle pressure—the pressure needed at the nozzle to achieve the desired GPM—and the entrance pressure from the pump. The sum gives the pump discharge pressure required to push the target GPM through the hose to the nozzle. Elevation changes and other losses can affect the numbers, so they’re accounted for as needed, but the core method relies on the charts plus the nozzle and entrance pressures to ensure the correct discharge pressure and flow at the nozzle.