Nema Guide for Proper Use of Smoke Detectors in Duct Applications

Purpose

• The purpose of the NEMA guide is to provide information about the appropriate use of duct-mounted smoke detectors. These special smoke detectors provide a type of protection that other systems can’t offer, but they are often misused. NEMA's intent is to educate fire protection engineers, mechanical and electrical engineers, fire alarm system designers and installers on the correct way to use the detectors and let them know about new ways to detect smoke in ducts.

Contents

• The NEMA Guide for Proper Use of Smoke Detectors in Duct Applications was published in 2008 and is about 25 pages in length. The booklet, which provides information on duct-mounted smoke detector placement, spacing, zoning and wiring, includes new information about improvements in detector technology. Additional information is provided about the characteristics of smoke in HVAC, how duct detection systems are used to control smoke, and testing, maintenance and service of detectors. A hard copy or an electronic version of the guide can be purchased by visiting NEMA’s website.

Detectors

• Duct smoke detectors are used in commercial buildings to determine whether smoke is present in the airstream of HVAC ductwork. The purpose of these specialized detectors is to keep smoke from spreading through the system and to expel it outside. Duct smoke detectors aren’t designed to substitute for area smoke detectors or provide early detection of a fire. They can detect smoke in the ductwork when the air is circulating, but not if the fans are turned off. They are also unable to detect smoke that is moving in other areas than through the ductwork, and they don’t work well when the air filters are dirty, because dirty filters restrict air flow.

Additional Documents

• Several documents in addition to the NEMA guide provide information about the installation and performance of duct smoke detectors. UL 268A, Standard for Smoke Detectors for Duct Application is available from Underwriter’s Laboratories, both in a hard copy and as an electronic copy. NFPA Standard 90A, Installation of Air Conditioning is available from the National Fire Protection Association.