A fire damper is installed in fire-resistive-rated assemblies where ducts penetrate or there are air transfer openings. Its purpose is to close automatically on detecting heat and help prevent the spread of fire through the opening. It does so using a design intended to interrupt migratory airflow, resist the passage of flame and maintain the integrity of the fire-rated separation. By minimizing the spread of smoke and flames, dampers aid the evacuation of a building and can reduce reconstruction costs to building owners.
Curtain Fire Dampers as the Industry Standard
Until recently, engineers could generally choose from two categories: curtain fire dampers and multiblade fire dampers. Curtain fire dampers have been the industry standard for more than 40 years. They consist of a series of interlocking blades that fold up into the top of the assembly unit to permit the maximum free area in an airway. A thermal release mechanism or fusible link holds them together. When temperatures reach approximately 165°F, the heat-sensitive fusible link separates and the blades fall, closing the airway and preventing fire from spreading.
Figure 1. Although widely adopted, the curtain-damper design presents commissioning and maintenance challenges.
Curtain fire dampers are designed to meet National Fire Protection Association (NFPA) and International Code Council (ICC) international building-code requirements, so they can serve wherever a fire damper is required—typically in fire-rated walls and in floors. Depending on the structure type and floor levels, fire-damper applications can vary and a single building may contain anywhere from a few fire dampers to several hundred. Curtain dampers represent a relatively inexpensive alternative to fire dampers.
Testing and Maintenance Can Be Challenging
Although curtain dampers are widely used, they have some drawbacks. The curtain-damper design presents a challenge in the unit’s commissioning and maintenance. As facility managers recognize the protection capabilities of fire dampers, more authorities having jurisdiction (AHJs) and building owners are requiring fire dampers to be operation tested and maintained regularly. Operational testing normally involves removing or activating the fusible link and letting the damper close. Once closed, the damper is reopened and the fuse link is replaced.
Figure 2. The mechanical design of the curtain damper further complicates the testing process, requiring two hands in the duct.
According to the NFPA 80 and 105 standard, all fire dampers in a building must be inspected and tested before occupancy and again one year later under normal operating conditions. Afterwards, the test and inspection frequency is every four years—except in hospitals, where it’s every six years. The challenge with testing fire dampers, as well as with maintenance, is that most of them are in areas of a building that are difficult to access, usually requiring a ladder. The mechanical design of the curtain damper further complicates the testing process, requiring two hands in the duct: first to move the blades from the groove and then to move them to the top of the frame, pushing them against the spring tension and attaching a new fuse link. In some cases, the damper must be removed from the duct to be reset.
All this activity can be a difficult, time-consuming and therefore expensive operation, depending on the number of dampers in a building. In particular, it can take anywhere from 15 minutes to an hour per damper.
Multiblade Fire-Damper Alternative
An alternative to the curtain fire damper is the multiblade fire damper. This damper uses a number of linked pivoting blades. Much like the blades of a curtain damper, they are released from their open position by a thermal release mechanism or fusible link, causing the damper to close. But the multiblade fire damper is built to handle higher pressure velocities—as high as 4,000 feet per minute (fpm) and 8" static pressure—and it can be larger than a curtain fire damper.
Just as importantly, maintenance of the multiblade fire damper requires less time and effort, thanks to a crank lever that makes it easier to hold and manipulate the blades back to the open position. This design makes removing the damper unnecessary for maintenance. One consideration, however, is that multiblade dampers can be more expensive.
New Fire-Damper Design Option
Just recently, a third fire-damper option became available to engineers—the DFD-LP dynamic fire damper low-profile. This damper uses a single blade and a fusible link that’s easier to reset than the curtain type. The DFD-LP offers easier maintainability, better performance and improved pressure-drop capabilities. What’s more, they’re less expensive than multiblade dampers.
Figure 3. The DFD-LP uses a single blade and a fusible link that is easier to reset than the curtain type. It can be installed both vertically and horizontally.
The DFD-LP is rated for 4,000 fpm specifications and a standard static pressure of 4" w.g. regardless of damper size. In addition, it offers the lowest pressure drop compared with B-style frame curtain horizontal dampers, enabling engineers to specify easier-to-install A-style frames. Like curtain and multi-blade dampers, the DFD-LP is 90-minute fire rated and meets all current building codes.
Specifying the Best Damper
Given these three fire-damper options, how can an engineer best determine which one to specify for a project? All three meet current building codes and the UL555 Test Standard, and all offer the same fire rating. The differences among them lie in their construction or design and how they perform.
In making a selection among the three dampers, an engineer should consider these questions:
- Which damper will meet their system conditions in terms of air velocity and pressure drop?
- How important is cost?
- How much time can they afford to invest in maintenance?
- Which one features more flexibility for the most user-friendly installation?
In the past, curtain fire dampers were the standard for building design. Today, other options exist and bring with them installation, performance and maintenance benefits that building owners can experience throughout the life of their buildings. By doing their homework and asking the right questions, engineers can specify the fire damper that will best serve the unique needs of the building and help protect building occupants.
About the Author
Mike Coyazo is product manager for Ruskin’s commercial and UL life-safety dampers. He has been with the company for over 17 years, primarily dedicated to life-safety dampers. Over the years, Mike has conducted numerous damper trainings for HVAC-industry professionals, including working with SMACNA’s Building Inspectors Program as well as participating in both ICC and NFPA code hearings.