Duct detectors are never required on the return air ducts when?

Duct detectors are never required on the return air ducts when?

• A. There are system smoke detectors that perform the shutdown function
• B. The building has no fire alarm system
• C. Duct detectors must always be required
• D. The sprinkler system is not present

Answer: (A)

The idea being tested is how HVAC shutdown is handled in a fire event. Duct detectors are used to stop air movement when smoke is detected in the ducts, but if the building already has system-wide smoke detectors that automatically shut down the HVAC, adding separate duct detectors on the return air ducts isn’t required. The system smoke detectors provide the necessary shutdown function, preventing further smoke spread through the return path, so duplicating with duct detectors would be redundant and unnecessary. That’s why the statement about system smoke detectors performing the shutdown is the correct reason for not needing duct detectors in the return air ducts. The other scenarios don’t establish an automatic, code-supported reason to skip duct detectors in the same way, so they don’t justify removing them.

The idea being tested is how HVAC shutdown is handled in a fire event. Duct detectors are used to stop air movement when smoke is detected in the ducts, but if the building already has system-wide smoke detectors that automatically shut down the HVAC, adding separate duct detectors on the return air ducts isn’t required. The system smoke detectors provide the necessary shutdown function, preventing further smoke spread through the return path, so duplicating with duct detectors would be redundant and unnecessary.

That’s why the statement about system smoke detectors performing the shutdown is the correct reason for not needing duct detectors in the return air ducts. The other scenarios don’t establish an automatic, code-supported reason to skip duct detectors in the same way, so they don’t justify removing them.