Airflow in ventilation ducts is far too fast for smoke detectors. The solution to this problem is to install the detector in a box with a device to slow airflow across the detector.
The
duct detector consists of a sealed box with a see-through cover that is installed on the returning air duct, a sampling tube for smoke input and a
smoke release tube, that are inserted into the duct via corresponding openings. The duct detector’s cover is translucent and allows for viewing of the chamber’s internals and the integral warning LED of the detector that is installed in it.
The DTH-400 / DTH-400A duct smoke detectors are intended to work with Telefire's conventional fire alarm control panels model GSA-2B and GSA-1000 (DTH-400) and analog addressable fire alarm control panels model ADR-3000 (DTH-400A).
The duct detector allows sampling of airflow in return air vents of central ventilation systems.
The duct detector allows the use of photoelectric (TFO-440 / TFO-440A) smoke detectors.