Duct Smoke Detector Make Up Air Unit

It is not the intent of section 606 to require duct smoke detectors in systems that function only as exhaust systems or only as makeup air systems.

Duct smoke detector make up air unit.

Testing air handling unit duct smoke detector. A duct smoke detector should shut off a typical blower and fresh air and turn on the exhaust. Duct detectors aren t a replacement for room sensors. Duct smoke detector are important part of a fire protection syste.

Nfpa 72 also states that a duct smoke detector is not allowed to replace an area smoke detector mainly because if the air handling unit ahu is not running the detector would not detect smoke. If the duct system is designed to carry more than 2000 cfm 5 tons nominal of air you need one in the return if imc is being followed and the supply if nfpa is being followed. The imc commentary provides further explanation on the intent of the code. A makeup air supply system that discharges 100 percent outdoor air into a building does not withdraw air from the building.

The detector shall be listed for the air velocity temperature and humidity anticipated at the point where it is installed. It is preferred that the occupied and non occupied areas and spaces have smoke detectors simply because the fans in air handlers or that move air through duct work may not be operational at all times so having smoke detectors in the duct work will not offer the amount of protection that smoke detectors would offer in the spaces or area served whether those areas or spaces are occupied or not. Where a smoke damper is installed within a duct a smoke detector shall be installed in the duct within 5 feet 1524 mm of the damper with no air outlets or inlets between the detector and the damper. A heating ventilating or air conditioning hvac fan motor overheats and resulting smoke is sensed by the duct smoke detector installed in the main supply duct.

Duct detectors smoke detection nfpa 90a code requirements. Ahu smoke detector must shutdown upon alarm. Therefore duct smoke detectors are typically considered mechanical equipment devices instead of life safety devices.