What is a Dynamic Fire Damper?

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Dynamic classic fire damper

In a world filled with uncertainties, it is crucial to take as many safety precautions as possible, particularly regarding buildings. Fire prevention may only be an exciting topic to sit around and discuss if you’re a fire safety professional, but the work that a dynamic fire damper does is well worth a chat. These small items can make the difference between people making it home after a fire event with a story to tell or not surviving at all.

What Are Fire Dampers?

Fire dampers are hardware utilized in any air transfer opening, duct, or other places where fire-rated structures such as floors, walls, or any other fire barrier are penetrated. Without the placement of the fire dampers, a fire would sweep quickly through the HVAC (heating, ventilation, and air conditioning) ductwork to other spaces in buildings and create a far greater danger to people and property. A fire damper assists in limiting the fire’s breadth and minimizes the extent of damage to the building, environment, and people.

How Does a Fire Damper Work? 

Fire dampers work on a simple principle. When they get too hot from the presence of a fire, they close, blocking off the fire so that it can’t proceed any further in the HVAC ductwork. They are designed to close when the surrounding temperature reaches a set threshold limit. Typically, it will be 165 degrees Fahrenheit, but in environments that routinely reach that temperature, such as kitchens or laundromats, it will be set higher, such as 212 degrees Fahrenheit.

When the set temperature is reached, the fusible link, which keeps the damper blades in place, will open. When the fusible link opens, the damper blades will close, preventing the smoke and fire from progressing further into the HVAC ductwork. Once the fire damper has been activated, it cannot be reset automatically. A qualified technician will need to come out to reset it manually.

What is a Fusible Link?

A fusible link is a mechanism that contains the damper blades of the fire damper and holds them in the open position until the fire damper is activated. Once the fusible link is in the presence of temperature at its set temperature point, the surround will melt or break apart, and the link will open. Once the link opens, the fire damper blades will close.

Underwriter Laboratories has set an international standard for fusible links, UL 33, that ensures all thermal links are reliable and sustainable, thanks to these four tests: 

  • Oil bath tests
  • Corrosion tests
  • Oven tests
  • Load tests

Types of Fire Dampers:

  • Static
  • Dynamic

What Makes a Dynamic Fire Damper Different?

What is the main thing that separates dynamic fire dampers from static ones? The types of HVAC systems where they are utilized. Static fire dampers are used in HVAC systems that will shut down automatically when a fire occurs.

The dynamic fire damper, like its name, will operate while the HVAC system is still running. It needs to have the capability to close while still having air running through the ducts. Therefore, dynamic fire dampers are spring-loaded, so they have the power to close against an air current. They have built-in fans that will turn on to activate the spring-loaded system.

Additionally, there is a difference in where you might find them. For example, static fire dampers tend to be in horizontal fire barriers, whereas you would find dynamic fire dampers in vertical barriers of your HVAC system. 

What Type of Blades Do Dynamic Fire Dampers Have?

When looking at dynamic fire dampers, there are two common types:

  • Curtain styles
  • Multi-blade

The curtain-style blades look like accordion stacks and are folded and held open at the top of the damper in order to allow airflow to move freely during regular HVAC system operation. However, when there is a fire and the set temperature is reached, the surround of the fusible link will melt, and the blade stack, activated either by an attached spring, the force of gravity, or by a combination of the attached spring and gravity will drop shut.

The multi-blade dynamic fire damper uses individual blades spaced apart and connected with a common linkage, allowing the blades to rotate open or close in unison, much like a louver. The linkage is connected to a spring-wound shaft held open with a fusible link.

Once the fusible link surround melts when it reaches the set temperature, the shaft spring will engage, triggering the damper blades to close. One of the benefits of the multi-blade dynamic fire damper is that it can also adjust the blades’ position manually, thus serving the same function as a balancing damper within your HVAC system.

What Tests Do Dynamic Fire Dampers Need to Undergo?

When looking at dynamic fire dampers, there are extensive tests they need to undergo. They require UL555 dynamic closure testing to form ratings for velocity and pressure. This dynamic closure test evaluates the ability of the dynamic fire damper to close under airflow. 

The airflow conditions for this test are developed by setting the velocity with the damper blades in the fully open position and then setting pressure with the damper blades fully closed. The damper will then be set to the open position, and the airflow will be applied.

The dynamic fire damper is tested in order to demonstrate complete closure against a prescribed airflow three times at ambient air conditions. It will then be tested a fourth time with heated air so that the damper’s fusible link melts and forces the damper to close.

How Do You Take Care of Dynamic Fire Dampers?

Making sure to have dynamic fire dampers as part of your fire safety plan is a wise choice, but you need to follow it up by having regular maintenance. The National Fire Protection Association requires, according to NFPA Code 80, that you have your dynamic fire dampers inspected one year after installation and then every four years after that. The only exception to this is hospitals; they get inspected one year after installation and every six years after that.

Dynamic fire dampers play a critical role in the protection of buildings. However, placing and maintaining them are equally important. Lloyd Industries is here to help you with any questions or concerns you might have. Please do not hesitate to reach out with any HVAC questions. In need of a contractor or technician? We have a vetted list of professionals available in your area!


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