Smoke Control and HVAC Systems Flashcards

Under NFPA 90A, an air-handling system with a capacity greater than what airflow requires a smoke detector in the supply air duct?

Answer: 2,000 cfm

NFPA 90A requires supply-side duct smoke detection on air distribution systems over 2,000 cfm.

Where is the supply-side duct smoke detector normally located?

Answer: Downstream of the air filters and ahead of any branch connections

Placing it after the filters and before branches lets it sample all supply air without filter clogging.

What is the primary function of a duct smoke detector?

Answer: To stop the spread of smoke through the HVAC system

Duct detectors are meant to shut down or control HVAC to prevent smoke distribution, not to serve as open-area protection.

A duct smoke detector is installed above a hard ceiling where it cannot be seen. What is typically required?

Answer: A remote alarm indicator or remote test station

Concealed duct detectors need a remote indicator so their activation can be seen and identified.

Return air systems over what capacity require smoke detectors at each story before connection to a common return?

Answer: 15,000 cfm

NFPA 90A requires return-side detection at each story for systems over 15,000 cfm serving more than one story.

Why must a duct smoke detector's sampling tube span the width of the duct?

Answer: To sample air across the full duct cross-section

Spanning the duct ensures representative air from the whole airstream reaches the sensing chamber.

Duct smoke detectors are listed for a specific range of what duct condition?

Answer: Air velocity

Each duct detector is listed for a minimum and maximum air velocity for proper sampling.