Which firemain pressure range is acceptable when reporting an AFFF station as ready?

• A. 150 +/- 15 psi
• B. 100 +/- 5 psi
• C. 200 +/- 20 psi
• D. 50 +/- 10 psi

Answer: (A)

The key idea here is that a firemain system is considered ready only when its pressure sits at the design level within a safe tolerance. For AFFF stations, this design pressure is about 150 psi, with a tolerance of plus or minus 15 psi. So the acceptable window is roughly 135 to 165 psi. Sticking to this range ensures the foam proportioner and ejector can draw and mix foam concentrate properly and deliver the correct flow through the nozzles, without overstressing pumps, piping, or fittings. If the pressure is much lower, the system may not pull concentrate correctly or provide enough flow; if it’s much higher, components could be stressed and foam proportioning could go off spec. Other options fall outside this optimal window, which is why they aren’t used to declare readiness.