FSD HVAC Systems & Airflow Control 2 — Questions and Answers
Question 1: Which NFPA standard governs the installation of fire dampers in HVAC duct systems?
- NFPA 13
- NFPA 90A (Correct answer)
- NFPA 72
- NFPA 101
Correct answer: NFPA 90A
NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems, governs fire damper installation in HVAC ductwork.
Question 2: A combination fire/smoke damper must comply with which UL standard?
- UL 555
- UL 555S
- UL 555C
- Both UL 555 and UL 555S (Correct answer)
Correct answer: Both UL 555 and UL 555S
Combination fire/smoke dampers must comply with both UL 555 (fire dampers) and UL 555S (smoke dampers) since they perform both functions.
Question 3: What is the primary purpose of an actuator on a motorized smoke damper?
- Provide manual override capability
- Open or close the damper blades upon receiving a control signal (Correct answer)
- Reduce airflow velocity through the duct
- Maintain blade temperature below fusible link rating
Correct answer: Open or close the damper blades upon receiving a control signal
The actuator is the electromechanical device that physically positions the damper blades open or closed in response to a control signal from the fire alarm or building automation system.
Question 4: In a variable air volume (VAV) HVAC system, why is damper leakage rating especially important?
- VAV systems operate at lower static pressures than constant volume systems
- Leakage affects the accuracy of zone temperature control and can compromise smoke containment (Correct answer)
- VAV boxes require dampers with higher temperature ratings
- Leakage ratings only apply to constant volume systems
Correct answer: Leakage affects the accuracy of zone temperature control and can compromise smoke containment
In VAV systems, damper leakage affects zone temperature accuracy and, critically, can allow smoke migration past a closed smoke damper during an emergency.
Question 5: A fire damper installed in a rated floor-ceiling assembly must achieve which minimum fire-resistance rating when the assembly is rated at 2 hours?
- 1 hour
- 1.5 hours
- 2 hours (Correct answer)
- 3 hours
Correct answer: 2 hours
Fire dampers must have a fire-resistance rating at least equal to the rating of the assembly in which they are installed; a 2-hour assembly requires a 2-hour damper.
Question 6: What does the term 'dynamic closure' mean for a smoke damper?
- The damper closes only after the fan shuts down
- The damper is rated to close against moving airflow without the system being de-energized first (Correct answer)
- The damper uses spring return to close automatically
- The damper requires manual reset after each closure event
Correct answer: The damper is rated to close against moving airflow without the system being de-energized first
Dynamic-rated smoke dampers (Class II) are tested and listed to close reliably against airflow while the fan is still running, unlike static-only dampers that require fan shutdown first.
Question 7: Which component in a fire damper provides the thermal trigger that causes the damper to close?
- Smoke detector
- Motorized actuator
- Fusible link (Correct answer)
- Limit switch
Correct answer: Fusible link
The fusible link is a heat-sensitive element that melts at a rated temperature (typically 165°F), releasing the damper blades to close under spring tension.
FSD HVAC Systems & Airflow Control 2
Which NFPA standard governs the installation of fire dampers in HVAC duct systems?