1.1 These requirements cover air duct smoke detectors intended for indoor use within or protruding into a duct, or mounted in a housing with sampling tubes extending into or traversing a duct. Air duct smoke detectors are intended to be installed in ducts where the maximum air temperature inside the duct does not exceed 100°F (38°C), nor does the minimum temperature become less than 32°F (0°C), in accordance with the Standard for Automatic Fire Detectors, NFPA 72, and the Standard for the Installation of Air Conditioning and Ventilating Systems, NFPA 90A.

1.2 An air duct smoke detector unit, as covered by these requirements, is intended to detect smoke for the primary purpose of controlling blowers and dampers of air conditioning and ventilating systems to reduce the risk of panic and damage from distribution of smoke and gaseous products. Each unit consists of an assembly of electrical components, including a sensing means to detect smoke (sensing head or projected beam assembly), sampling tubes or equivalent (based on design), provision for connection to a source of power, and means for generating a signal when smoke is detected. It is not prohibited that remote control circuits be provided. A detector shall be powered from a commercial power source, separate power supply, or be connected to a control unit as part of a fire protection signaling system. Duct detectors are not intended as a substitute for open area protection.

1.3 These requirements cover detectors:

1. a) Intended to control air conditioning and ventilating systems,

2. b) Intended for control of releasing devices, such as fire and smoke dampers, or

3. c) Both (a) and (b).

1.4 These requirements do not cover:

1. a) Control units that are covered by the Standard for Control Units and Accessories for Fire Alarm Systems, UL 864, to which the air duct smoke detectors are connected.

2. b) Single and multiple station smoke detectors covered by the Standard for Smoke Alarms, UL 217.

3. c) Smoke detectors intended for open area protection or releasing device service, or both, covered by the Standard for Smoke Detectors for Fire Alarm Systems, UL 268.

4. d) Smoke detectors integral with combination door closers and holders, covered by the Standard for Door Closers-Holders, With or Without Integral Smoke Detectors, UL 228.

5. e) Commercial-resident detectors not intended for connection to a system control unit that are covered by the Standard for Smoke Detector Monitors and Accessories for Individual Living Units of Multifamily Residences and Hotel/Motel Rooms, UL 1730.