FST Smoke Detection 5 — Questions and Answers
Question 1: A duct smoke detector that shuts down the HVAC system upon activation is functioning as which type of control?
- Supervisory control
- Releasing control
- Smoke control (Correct answer)
- Alarm initiation only
Correct answer: Smoke control
Duct smoke detectors that shut down HVAC fans are acting as smoke control devices, preventing the distribution of smoke through the ductwork system.
Question 2: What is the FIRST step a technician should perform when a smoke detector reports a 'trouble' condition at the fire alarm control panel?
- Replace the detector
- Reset the panel and observe whether the trouble clears
- Perform a sensitivity test on the detector
- Inspect wiring and the detector for loose connections, contamination, or cover removal (Correct answer)
Correct answer: Inspect wiring and the detector for loose connections, contamination, or cover removal
A trouble condition typically indicates a wiring fault, missing cover, loss of power, or internal fault; physical inspection is the correct first diagnostic step.
Question 3: Under NFPA 72, which type of signal does a smoke detector supervisory device in an HVAC system generate when smoke is detected?
- Supervisory signal
- Alarm signal (Correct answer)
- Trouble signal
- Presignal
Correct answer: Alarm signal
Duct smoke detectors initiate an alarm signal when smoke is detected, even though their primary function is HVAC control — they are alarm initiating devices.
Question 4: When installing smoke detectors in a compartment with a ceiling height of 14 feet, which NFPA 72 adjustment is required?
- No adjustment — standard spacing applies up to 30 feet
- Reduce spacing based on the high-ceiling correction factor in NFPA 72 Annex A (Correct answer)
- Switch to heat detectors only above 12 feet
- Install only projected beam detectors above 12 feet
Correct answer: Reduce spacing based on the high-ceiling correction factor in NFPA 72 Annex A
NFPA 72 Annex A provides spacing reduction factors for ceiling heights above 10 feet to account for smoke dilution and stratification in taller spaces.
Question 5: Which scenario would MOST likely cause a carbon monoxide detector to activate but NOT a smoke detector?
- A smoldering mattress fire
- A car left running inside an attached garage (Correct answer)
- A fast-flaming paper fire
- A deep-seated electrical cable fire
Correct answer: A car left running inside an attached garage
A running vehicle produces high CO levels without significant visible smoke, triggering a CO detector while generating insufficient aerosol to activate a smoke detector.
Question 6: What is the minimum required separation distance between a smoke detector and the nearest sprinkler head deflector under NFPA 72?
- 12 inches horizontally
- 18 inches horizontally (Correct answer)
- 24 inches horizontally
- 36 inches horizontally
Correct answer: 18 inches horizontally
NFPA 72 requires smoke detectors to be installed at least 18 inches horizontally from any sprinkler deflector to prevent sprinkler water spray from directly impacting and damaging the detector.
Question 7: Which document provides the primary installation and testing requirements for smoke detectors in commercial fire alarm systems in the United States?
- NFPA 101 — Life Safety Code
- NFPA 13 — Standard for the Installation of Sprinkler Systems
- NFPA 72 — National Fire Alarm and Signaling Code (Correct answer)
- IBC Chapter 9
Correct answer: NFPA 72 — National Fire Alarm and Signaling Code
NFPA 72 is the primary national standard governing the installation, testing, inspection, and maintenance of fire alarm and signaling systems including smoke detectors.
FST Smoke Detection 5
A duct smoke detector that shuts down the HVAC system upon activation is functioning as which type of control?