CFPS Water-Based Suppression Systems 3 — Questions and Answers
Question 1: In hydraulic calculations for sprinkler systems, what does the Hazen-Williams formula calculate?
- Sprinkler thermal response time index (RTI)
- Friction loss per foot of pipe (Correct answer)
- Sprinkler K-factor discharge coefficient
- Water hammer pressure transients
Correct answer: Friction loss per foot of pipe
The Hazen-Williams formula (p = 4.52 × Q^1.85 / (C^1.85 × d^4.87)) calculates friction loss per unit length of pipe based on flow, diameter, and pipe material coefficient.
Question 2: A sprinkler has a K-factor of 5.6 and is discharging at 25 psi. What is the approximate flow rate using Q = K × √P?
- 14 gpm
- 28 gpm (Correct answer)
- 56 gpm
- 7 gpm
Correct answer: 28 gpm
Using Q = K × √P: 5.6 × √25 = 5.6 × 5 = 28 gpm — the fundamental sprinkler discharge formula.
Question 3: What is the Hazen-Williams C-factor assigned to new black steel (Schedule 40) pipe per NFPA 13?
- 100
- 120 (Correct answer)
- 140
- 150
Correct answer: 120
NFPA 13 assigns a Hazen-Williams C-factor of 120 to new black steel pipe, reflecting its moderate interior smoothness.
Question 4: In a hydraulically designed sprinkler system, what does the term 'remote area' refer to?
- Sprinklers farthest from the building's main entrance
- The hydraulically most demanding zone that must receive the full design density (Correct answer)
- Any sprinkler located more than 500 feet from the water supply
- Sprinklers on branch lines beyond the cross-main
Correct answer: The hydraulically most demanding zone that must receive the full design density
The remote area is the hydraulically most demanding design area; proving adequate density there confirms the entire system is adequately supplied.
Question 5: Per NFPA 15, water spray fixed systems are designed to provide:
- A replacement for wet pipe systems in large industrial facilities
- Fire suppression on specific hazards only, with no exposure protection role
- Both direct fire suppression on specific hazards and exposure protection of adjacent equipment or structures (Correct answer)
- Water supply backup to deluge and pre-action systems
Correct answer: Both direct fire suppression on specific hazards and exposure protection of adjacent equipment or structures
NFPA 15 water spray systems serve dual roles: suppressing fires on specific hazard targets and protecting adjacent equipment or structures from heat exposure.
Question 6: What is the primary purpose of a pressure-reducing valve (PRV) installed at a standpipe hose valve outlet?
- Increase outlet pressure to compensate for high-rise elevation losses
- Limit outlet pressure to safe levels for hose line handling and nozzle operation (Correct answer)
- Prevent backflow into the public water supply
- Automatically activate the standpipe system upon detection
Correct answer: Limit outlet pressure to safe levels for hose line handling and nozzle operation
PRVs on standpipe outlets limit pressure to safe levels, protecting firefighters from dangerously high nozzle reaction forces caused by excessive supply pressure.
Question 7: Per NFPA 13, what design density and remote area size apply to an Ordinary Hazard Group 2 occupancy?
- 0.10 gpm/ft² over 1,500 sq ft
- 0.15 gpm/ft² over 1,500 sq ft
- 0.20 gpm/ft² over 1,500 sq ft (Correct answer)
- 0.30 gpm/ft² over 2,500 sq ft
Correct answer: 0.20 gpm/ft² over 1,500 sq ft
NFPA 13 prescribes 0.20 gpm/ft² over a 1,500 sq ft remote area as the minimum design criteria for Ordinary Hazard Group 2 occupancies.
CFPS Water-Based Suppression Systems 3
In hydraulic calculations for sprinkler systems, what does the Hazen-Williams formula calculate?