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According to the “Size Does Matter” campaign, IMC (Chapter 606.3) and NFPA 72 (Chapter 184.108.40.206) codes require that all smoke detector installations, tests, and inspections be made in accordance with the manufacturer’s published instructions.
In most cases, manufacturer specs call for the air sampling tube to extend between 2/3 and 80 percent of the duct width. If the sample tube does not span the width of the duct, smoke can bypass the sample tube and avoid immediate detection, allowing the fire to progress. In addition to this potential liability, improperly sized sampling tubes can result in failed inspections, increased job costs, and jeopardized inspector relationships.
Some manufacturers supply sample tubes with duct smoke detector purchases. However, the standard sample tube supplied is approximately 12 inches in length, meaning it is only code-compliant in ducts up to 18 inches wide. Particularly in commercial applications, where duct widths are more commonly 36 inches wide, the supplied sample tube would not meet code.
APC’s campaign urges inspectors to take application duct size into account when determining if the standard air sampling tube length is sufficient. All manufacturers that supply air duct smoke detectors offer air-sampling tubes that will accommodate duct widths of up to 10 feet.
According to APC, tubes can always be cut down to size, and in some cases, two metal tubes may be spliced together to meet distance requirements.
For more information, visit www.ap-c.com.
Publication date: 03/10/2008