Which statement best describes detectors in air duct systems in relation to room smoke detectors?

• A. They are substitutes for room smoke detectors
• B. They are not substitutes for room smoke detectors
• C. They are for exterior use only
• D. They are irrelevant to fire alarms

Answer: (B)

Air duct detectors monitor smoke in the building’s ventilation system, not in the rooms where people are. Because of that, they help control smoke movement and can trigger the fire alarm or shut down the HVAC, but they do not replace room smoke detectors. Room detectors provide immediate sensing where people are, which is essential for early warning and life safety. Duct detectors are used in addition to room detectors to improve overall protection, not as substitutes. They aren’t intended for exterior use, and they are relevant to fire alarms because they can influence how the system responds to smoke.