HVAC air ducts transfer conditioned air to occupied spaces in a building. In the event of a fire, air ducts can also transfer harmful—and even deadly—smoke, toxic gases, and flames to those same occupied spaces. National and local safety codes and standards address this issue by specifying the use of duct smoke detectors to help prevent injury, panic, and property damage. To prevent the spread and recirculation of smoke and other products of combustion, duct smoke detectors are used to shut off air handling systems, fans, and blowers when necessary. Duct detectors are often connected to the building’s fire alarm system and may also be a part of a control system designed to exhaust smoke to the outside of the building. Duct smoke detectors are not to be used as a substitute for open area protection or early warning detection nor are they a substitute for a building’s regular fire detection system.

To detect smoke, detectors consisting of a sensor within an enclosure are mounted outside of the duct. Sampling tubes connected to the detector enclosure penetrate and traverse the duct to draw air into the detector, sample it, and then return it
to the air stream. When particles of smoke suspended in the air reach the alarm threshold of the detector, an alarm signal is initiated, and appropriate action can be taken to turn off equipment and alert the building’s fire alarm control panel.

Regardless of the sensing technology used, a duct smoke detector must be installed in a location that will ensure the detector monitors representative samples of
air flowing through the duct. There are several factors to be considered when selecting a detector location in a duct.

• Dilution: Duct smoke detectors will alarm only when combustion particles make up a specified percentage of the sampled air. If circulated air mixes with fresh outside air, the combustion particle concentration can dilute and prevent a detector from sensing a fire condition. To avoid dilution, detectors should be located before fresh air intakes and before the exhaust air output.

• Stratification: Within a duct, air and combustion particles may stratify, preventing proper air sampling. To get a representative air sample, locate the detector between six and 10 duct widths downstream from a bend or other obstruction in the duct. 

• Excess humidity: High levels of humidity or condensation within the duct can cause false alarms. Duct smoke detectors should be located a minimum of 10 feet downstream of humidifiers. 

• Air filters: Air filters within ducts tend to collect flammable materials
  like paper, lint, and trash. Detectors should be installed downstream of filters to detect fires occurring in the filters. Regular filter maintenance is critical since reduced air flow due to clogged filters could prevent correct operation of the duct detector. 

• Air velocity: Duct smoke detectors are designed to be used in air handling systems having a certain range of air velocities, usually 500 to 4000 fpm. For applications down to 100 fpm, low-flow technology detectors are available.

Finally, when applying, installing, testing, and maintaining duct smoke detectors, be careful to follow the detector manufacturer’s instructions and adhere to National Fire Protection Association standards National Fire Alarm Code (NFPA 72) and Standard for the Installation of Air Conditioning and Ventilating Systems (NFPA 90A). Copies of the standards can be ordered from www.nfpa.org.

Kele offers a variety of duct smoke detectors and accessories.

The Farmer’s Almanac recently “branded” the upcoming winter of 2019-2020 a “Polar Coaster”  (open in separate tab) thanks to expected ups and downs in temperature. According to editor, the extended forecast will be “another freezing, frigid, and frosty winter for two-thirds of the country.” The coldest weather should run from late January through the beginning of February. While the biggest drop in temperature is expected across the northern Plains to the Great lakes, the Northeast will experience colder-than-normal temperatures.

Thank goodness it’s only September, right? You have time to inspect and replace the numerous components critical to keeping your facilities and HVAC systems—and the good folks who depend on them—fully functional. It does not matter what type of building—school, healthcare facility, or other commercial facility—the time to act is now!

Below is a list of key components to inspect. If you have questions, call Kele’s technical service team for expert advice on anything from inspection to maintenance to replacement. Kele can get your replacement parts to you fast, before the “Polar Coaster” takes off.

Inspect these components for winter season: 

• Valves
• Sensors
• Pneumatics
• Freeze stats

Other boiler peripherals: alarms and indicators and emergency shutdown devices.

Find what you need from the product categories Kele offers or shop now.

SAFETY REMINDER!

When was the last time your fire and smoke damper actuators were inspected?

National Fire Protection Code and Standards state the requirement for testing fire and smoke systems and dampers is one year after installation and then every four years (hospitals must inspect every six years). Now is the time to make sure your fire and smoke safety systems are up to code.

NATIONAL FIRE PROTECTION AGENCY CODES NFPA 105 AND NFPA 80

FURTHER READING:

Back to Basics: Process Tips for Periodic Inspection of Fire and Smoke Dampers

Guidance for Inspecting and Maintaining Fire and Smoke Actuators and Dampers

1. Verify that there is full unobstructed access to the damper
2. Test the damper with normal HVAC airflow and verify that it opens following either Option 1 or Option 2. There should be no interference due to rust, damaged frame or blades, or other moving parts.

OPTION 1: Dampers with position indication wired to indication lights or control panels:

• Switches can be wired to local or remote-control panels or building automation systems (BAS) to indicate that the damper is in the fully-open position, fully-closed position, or neither.
• Use the signal from the damper’s position indication device to confirm that the damper is in the fully-open position.
• Remove electrical power or air pressure from the actuator to allow the actuator’s spring return feature to close the damper.
• Use the signal from the damper’s position indication device to confirm that the damper reaches its fully- closed position.
• Re-apply electrical power to re-open the damper.
• Use the signal from the damper’s position indication device to confirm the damper reaches its fully-open position.

OPTION 2: Dampers without position indication:

• Visually confirm that the damper is fully-open position.
• Ensure that all obstructions, including hands, are out of the path of the damper blades.
• Remove electrical power or air pressure from the actuator to allow the actuator’s spring return feature to close the damper.
• Visually confirm that the damper closes completely.
• Re-apply electrical power to re-open the damper.
• Visually confirm that the damper is in the fully open position.

3. If the damper is not operable, it must be repaired as soon as possible. If the actuator has failed, replace it with a UL-approved actuator. After these repairs, the damper should be tested again.

4. If there is a latch, verify that it is operable.

5. Perform any other damper manufacture-recommended maintenance such as lubrication.

6. Following the test and any repairs, document the location of the damper, the date, the inspector, and deficiencies or repairs. Keep the record for the life of the damper and have it available as you may need to show it to an inspector.

If you need assistance, contact Kele’s technical service team. We’re here to help.