What residual pressure is required when computing available water supply in a specific area?

What residual pressure is required when computing available water supply in a specific area?

• A. 10 psi
• B. 20 psi
• C. 30 psi
• D. 40 psi

Answer: (B)

In calculating available water supply, you must assume a minimum pressure that will remain in the system at the most remote point to account for losses from friction and elevation. This residual pressure ensures the fire protection system still has usable pressure when water is delivered to the farthest outlet. The standard value used for this residual pressure in NFPA-based calculations is 20 psi. It strikes a balance by being low enough to reflect practical losses but high enough to ensure firefighting outlets still receive meaningful pressure. Using a lower residual pressure would overstate the available water supply, while a higher one would understate it and be overly conservative. Therefore, 20 psi is the appropriate residual pressure to use.

In calculating available water supply, you must assume a minimum pressure that will remain in the system at the most remote point to account for losses from friction and elevation. This residual pressure ensures the fire protection system still has usable pressure when water is delivered to the farthest outlet.

The standard value used for this residual pressure in NFPA-based calculations is 20 psi. It strikes a balance by being low enough to reflect practical losses but high enough to ensure firefighting outlets still receive meaningful pressure. Using a lower residual pressure would overstate the available water supply, while a higher one would understate it and be overly conservative. Therefore, 20 psi is the appropriate residual pressure to use.