What is a duct smoke detector and where is it typically installed?

• A. A detector installed in the lobby to sense smoke at human level.
• B. A detector installed in HVAC ducts to sense smoke before it reaches occupied spaces, typically in supply and return ducts.
• C. A detector installed on the roof for outdoor smoke.
• D. A detector that senses smoke in electrical rooms only.

Answer: (B)

Duct smoke detectors sample air inside the building’s HVAC ducts, so they can sense smoke before it reaches occupied spaces. They’re typically mounted in supply and return ducts, placing detection right where air moves through the system. This allows for early warning and often enables automatic actions like triggering alarms and shutting down or isolating fans to prevent smoke from spreading. Detectors placed in a lobby, on a roof for outdoor smoke, or only in electrical rooms wouldn’t provide this early, centralized detection through the ventilation system.