Fire Damper vs. Fire Smoke Damper

Do you know the difference between fire dampers and fire smoke dampers?

This is a questions that seems to come up a lot in the fire alarm install and design world.  The definition of a damper is "A person or thing that damps or depresses".  In other words it is a plate that is placed within the duct work of an HVAC system to regulate or in some cases stop air flow.

Now in the fire alarm industry we are more concerned with the terms "Fire Damper", "Smoke Damper" or "Combination Smoke Fire Damper".  Whats is the difference?  Well it is actually quite simple as we explain below.

• A "Fire Damper" as defined in the CMC (California Mechanical Code) 2022 Edition Section 206.0 - "An automatic-closing metal assembly of one or more louvers, blades, slats or vanes that close upon detection of heat so as to restrict the passage of flame and is listed to the applicable recognized standard."  The automatic means can be accomplished one of two ways: 1) by a fusible link that will melt upon heat thus releasing the louvers into the closed position.  2)  by motorized actuators that will close upon loss or gain of power.  These are typically controlled by and addressable relay module.

• A "Smoke Damper" as defined in the CMC (California Mechanical Code) 2022 Edition Section 206.0 - "A damper arranged to seal off airflow automatically through a part of an air duct system so as to restrict the passage of smoke and is listed to the applicable recognized standard."

• A "Combination Fire Smoke Damper" is exactly that, a combination of a "Fire Damper" and a "Smoke Damper".

When are they required and how do I know when to use what type?

Keep in mind that the fire alarm contractor will not be providing or installing these.  However, it is nice to know what to look for on a bid set of plans or during a job walk.  First up is the "Fire Damper".  A fire damper is installed in HVAC duct work at the intersection of a rated barrier such as walls or partitions.  The damper is in place to secure the integrity of the rated barrier in the event of heat or flames around 165 degrees F.  Like we stated above, the fusible link will melt thus releasing the louvers on the damper.  Once the louvers are closed or shut, the fire barrier is now secured from allowing flames to penetrate prior to the rating level of the barrier itself.

Smoke dampers are similar however, they close in the presence of smoke.  Now since the smoke damper cannot obviously sense smoke, we need to install a smoke detector. The smoke detector can either be a system smoke (tied to a building fire alarm system) or a stand alone smoke solely in place to activate the smoke damper.  Smoke Dampers are required to be installed on walls that separate smoke barriers.  

What's a smoke barrier you ask......  A smoke barrier is a continuous surface such as a wall, floor, or ceiling constructed to restrict the movement of smoke.  A smoke barrier can be either vertical or horizontal. 

Now a "combination smoke fire damper" is located in a situation where both fire rating and smoke barriers come into play.  A combination fire smoke damper also needs a smoke detector just like the smoke damper.  The smoke detector can either be a duct smoke detector (System Sensor D4120 or DNR) or a pendant mounted detector within the duct work itself.  Once the detector senses smoke particles it will either through programming or local relay base close the damper louvers.

Drywall Dust Problems with System Sensor Smoke Detector

If any packaged air conditioning units are run during the drywall installation phase of building construction to assist in the drying of joint compound, the fine dust created by sanding of those drywall joints may compromise the System Sensor smoke detector sensor heads within the duct housing. The 2D51 System Sensor Head in the InnovairFlex Duct Smoke Detector models D4120, D4120W and D4S may display a “maintenance” condition that will require replacement or cleaning of the sensing chambers on the smoke detector head. The “maintenance” condition will be indicated on the fire alarm control panel, on the sensor itself or power board of the duct smoke detector (the sensor LED will blink “red” every five seconds and the power board LED will blink “amber” every five seconds).

To avoid this condition, it is recommended that the System Sensor smoke detector heads be removed during the construction phase and replaced once construction is completed and the Certificate of Occupancy is issued. The sensor heads twist out for removal and twist in for insertion.

Below is an extracted image of the System Sensor duct smoke detector sensor head:


Cleaning the sensing chamber on the sensor head

If the System Sensor smoke detector heads are not removed during the construction phase and the sensor chamber becomes dirty causing a maintenance condition (it will not always be visible on the exterior black screen on the sensor head), the sensor head must be cleaned with compressed air. To clean the sensor head chamber, follow these step-by-step instructions see the video demonstration below:

1. Remove the System Sensor smoke detector head to be cleaned from the duct smoke detector housing by twisting it in a counterclockwise direction.
2. Remove the smoke sensor cover by pulling outward on each of the four removal tabs that hold the cover in place.
3. Vacuum the screen carefully without removing it. If further cleaning is required continue with Step 4. Otherwise, skip to Step 7.
4. Remove the chamber cover/screen assembly by pulling it straight out.
5. Use a vacuum cleaner or compressed air to remove dust and debris from the sensing chamber.
6. Reinstall the chamber cover/screen assembly by sliding the edge over the sensing chamber. Turn until it is firmly in place.
7. Replace the cover using the holes for the LEDs for alignment and then gently push it until it locks into place.
8. Reinstall the System Sensor smoke detector head in the duct smoke detector housing by aligning it in the housing and twisting it in a clockwise direction.

Note: Cleaning only the sensor head’s exterior black screen will not remove any drywall dust in the smoke sensing chamber.
Note: Should the System Sensor duct smoke detector remain in a “maintenance” condition after cleaning, then it may require the complete replacement of the sensor head. The replacement sensor head is model 2D51.

Tags: system sensor, system sensor smoke detector, Duct Smoke Detector, smoke sensor

Duct Smoke Detectors and LED Test Plates

Duct smoke detectors are a common device found in most fire alarm systems from the past and present. Whether the duct smoke detector is addressable or conventional, they both work the same way. A sample tube is inserted into the duct work and samples the air for smoke. If smoke is detected then the photoelectric smoke detector head within the duct smoke detectors sends an alarm signal to the fire alarm panel and shuts down the air conditioning unit.

With that said, most of these duct smoke detectors are located in areas that are not very easily accessed. These areas could include areas such as above t-bar or hard lid ceilings, attic spaces or roof tops. If the actual duct detector is located above a ceiling then access hatches or panels must be provided for obvious reasons. Also if the duct smoke detector is located in an area out of sight then you must provide a detailed description of the device location within the fire alarm control panel program as well as a remote LED plate on the ceiling below the device. This will assist the fire department, end user and technician locate the device. In fact, some jurisdictions such as L.A. County are requiring the remote LED plate to be installed any time you have a duct smoke detector above a ceiling and out of plain view.

With all of this information it is hard for me to understand how some of these local fire alarm installation companies are getting away with installing the remote LED plates on the wall directly above the thermostat controls for the particular HVAC unit. This picture was taken at a local restaurant in the Valencia, CA area. Now with these remote LED plates installed on the wall it makes it easy for fire alarm testing but it totally eliminates their true purpose. If there is a fire reported at the building with a signal coming from a duct smoke detector then the fire department is going to want to know exactly where it's location is the minute they enter. The LED on the wall does not exactly help.

System Sensor Duct Detector Applications

System Sensor Duct Detector Applications

NFPA 90A2, “Standard for the Installation of Air Conditioning and Ventilating Systems”, specifies that “Smoke detectors listed for use in air distribution systems shall be located as follows:

(1) Downstream of the air filters and ahead of any branch connections in air supply systems having a capacity greater than 2,000 cfm (944L/sec).

(2) At each story prior to the connection to a common return and prior to any recirculation or fresh air inlet connection in air return systems having a capacity greater than 15,000 cfm (7080 L/sec), and serving more than one story.”

Exception Number One:

“Return system smoke detectors are not required when the entire space served by the air distribution system is protected by a system of area smoke detectors.” (NFPA 90A, 2002, 6.4.2.2)

Exception Number Two:

“Fan units whose sole function is to remove air from inside the building to outside the building.” (NFPA 90A, 2002, 6.4.2.3)

Application Documents

There are several important documents that provide guidance concerning the performance, application and installation of System Sensor duct smoke detectors:

• U.L. Standard 268A, Standard for Smoke Detectors for Duct Applications

• NFPA Standard 90A, Installation of Air Conditioning and Ventilating Systems

• NFPA 92A, Standard for Smoke-Control Systems Utilizing Barriers and Pressure Differences Nfpa 92A: Recommended Practice for Smoke-Control Systems (Gl-92a-88)

• NFPA 92B Standard for Smoke Management Systems in Malls, Atria, and Large Spaces NFPA 92B: Standard for Smoke Management Systems in Malls, Atria and Large Spaces (2009)

• NFPA Standard 72, National Fire Alarm Code

• NFPA Standard 101, Life Safety Code

• ASHRAE Handbook and Product Directory, “Fire and Smoke Control”