FSD HVAC Systems & Airflow Control 3 — Questions and Answers
Question 1: A smoke damper installed in a smoke control system must be capable of holding which minimum leakage class per UL 555S?
- Class I
- Class II
- Class III (Correct answer)
- Class IV
Correct answer: Class III
UL 555S requires smoke dampers used in smoke control systems to meet at least Class III leakage (less than 4 cfm/ft² at 1" w.g.), though Class I or II provides better performance.
Question 2: When a smoke damper is used in a pressurized stairwell smoke control system, which operational mode is most common?
- The damper opens on fire alarm to vent smoke from the stairwell
- The damper remains closed to maintain positive pressure in the stairwell (Correct answer)
- The damper cycles open and closed to equalize pressure
- The damper reverts to 50% open position during alarm
Correct answer: The damper remains closed to maintain positive pressure in the stairwell
In pressurized stairwell systems, smoke dampers are kept closed on the stairwell side to maintain positive pressure, preventing smoke from entering the egress path.
Question 3: What is the maximum duct velocity at which a fire damper is considered to be operating in a 'static' system for UL 555 listing purposes?
- 500 fpm
- 1,000 fpm
- 2,000 fpm
- There is no velocity limit for static systems (Correct answer)
Correct answer: There is no velocity limit for static systems
For static fire damper installations, the fan must shut down before the damper closes; the UL 555 static listing does not specify a maximum duct velocity because closure occurs with no airflow.
Question 4: Which building system typically provides the control signal that causes a smoke damper to close during a fire event?
- Sprinkler flow switch only
- Thermostat setpoint
- Fire alarm control panel (FACP) (Correct answer)
- Building automation system humidity sensor
Correct answer: Fire alarm control panel (FACP)
The fire alarm control panel monitors smoke detectors and, upon detection, sends a control signal to smoke damper actuators to close them as part of the smoke control sequence.
Question 5: Duct smoke detectors used to initiate smoke damper closure must be listed under which standard?
- UL 268A (Correct answer)
- UL 217
- UL 521
- UL 268
Correct answer: UL 268A
UL 268A, Smoke Detectors for Duct Application, covers detectors designed to sample air within HVAC ducts and trigger smoke damper closure.
Question 6: In a return-air plenum system, why is fire damper installation at rated wall penetrations critical?
- Return plenums operate at positive pressure, which opens fire dampers
- Plenums can spread smoke and hot gases rapidly throughout the building (Correct answer)
- Return air is cooler, so fusible links must be rated lower
- NFPA 90A exempts plenum penetrations from damper requirements
Correct answer: Plenums can spread smoke and hot gases rapidly throughout the building
Return air plenums act as large, connected pathways above ceilings; without dampers at rated wall penetrations, they can carry smoke and combustion gases across fire barriers to remote areas.
Question 7: A fire damper sleeve must extend beyond the face of the wall or floor assembly by a minimum of how many inches on each side per most installation listings?
- 1 inch
- 3 inches (Correct answer)
- 6 inches
- No extension is required
Correct answer: 3 inches
Most UL-listed fire damper installations require the sleeve to extend at least 3 inches beyond each face of the wall or floor to ensure the damper frame is properly anchored within the assembly.
FSD HVAC Systems & Airflow Control 3
A smoke damper installed in a smoke control system must be capable of holding which minimum leakage class per UL 555S?