FireOps CalcHose sections = Number of engines − 1
Distance between engines = Total relay distance ÷ hose sections
Section PDP = Section FL + Target Intake ± Elevation + Device Loss
Step-by-step process
Enter total distanceMeasure or estimate the total distance from source engine to receiving engine.
Enter number of enginesInclude the source engine, relay engines, and receiving/attack engine.
Calculate sectionsA 3-engine relay has 2 hose sections.
Find spacingDivide total distance by the number of sections for basic equal spacing.
Calculate each section PDPEach engine supplies the next section and should maintain the target intake at the next engine.
Worked example
Total distance2000 ft
Engines3
Sections2
Distance between engines1000 ft
Target intake20 PSI at next engine
Real layouts may be uneven. A good calculator should also allow manual section distances, such as 800 ft then 1200 ft.
Common mistakes to avoid
- Using a default nozzle pressure that does not match the actual nozzle.
- Forgetting extra hose, elevation, or appliance loss.
- Using textbook coefficients when your department has known hose data.
- Treating a training estimate as a replacement for department SOPs or instructor direction.
How FireOps Calc helps
FireOps Calc is built to make this process faster on a phone. Open the web calculator, enter your hose, nozzle, flow, elevation, and appliance values, then review the math breakdown instead of only seeing a final number.
FAQ
Does number of engines include the receiving engine?
Yes. For FireOps Calc relay layout, number of engines means all pumpers in the relay, including source and receiving engines.
Why show each engine section?
Each section has its own friction loss and PDP, which makes the relay easier to teach and troubleshoot.