The Four Types of UL Life Safety Dampers

In this article, we cover the four main types of UL life safety dampers: fire, smoke, combination fire-smoke, and ceiling radiation dampers. Learn where life safety dampers go, what they do, and how they protect your building during a fire.

Life Safety Dampers & Passive Fire Protection

Passive Fire Protection (PFP) systems contain fire and smoke to predetermined areas of a building, to prevent it from quickly spreading through the rest of the building. Life safety dampers are installed in HVAC ducts and wall penetrations to support the PFP system. There are four types of UL life safety dampers: fire dampers, smoke dampers, combination fire-smoke dampers, and ceiling radiation dampers.

Buildings will require life safety dampers in specific areas, such as a fire barrier, to create special zones for fire and smoke containment. Each damper type will perform a particular function in a complete PFP system, but their purpose is the same: to give people time to evacuate the building. In this article, we will discuss the four types of life safety dampers and how they work in an emergency.

1.) Fire Dampers

In PFP systems, fire barriers are constructed to contain flames to a specific area of the building. These barriers will have penetrations, like HVAC vents, to allow for ventilation during standard operation.

Flames will infiltrate unprotected penetrations and pass through the barrier into other parts of the building. Fire dampers complete the fire barrier by protecting these penetrations. Each fire damper undergoes rigorous testing in a UL-approved laboratory, in accordance with UL 555, to be approved for use as a fire damper. Fire dampers will come in two distinctive styles, with multiple blades or with a curtain blade.

Fire dampers with multiple blades will resemble air control dampers: they have blades that rotate along a central axis, which are all contained in the metal frame. Multi-blade fire dampers can also have an actuator to control blade movement. All life safety dampers will use blade seals of a distinct color than air control dampers. This makes it easier to differentiate between them when installed in the ductwork. The main difference is their function. Unlike control dampers, fire dampers will only close when temperatures rise above a certain threshold. 

Each fire damper will have a heat response device (HRD) that holds the blades in the open position. Once temperatures in the duct exceed the HRD’s threshold, the device will release the blades to close off the duct. Multi-blade fire dampers will use actuators equipped with a thermodisc, an electrical HRD that disrupts the actuator's power supply. When the actuator loses power, springs inside the actuator will drive the damper blades to the closed position. This type of closure is called “power open – spring close”. 

Curtain Fire Dampers

Curtain blade fire dampers utilize several interlocking blades that form a curtain. This curtain is held to the top of the damper when open, to free the air stream of obstructions. During a fire, the curtain blade falls across the damper’s opening and closes off the duct. Special damper sleeves, C-Style, can conceal the blade stack and further increase the damper’s free area up to 100%.

The curtain blade is held in place with a fusible link that breaks apart when temperatures reach the link's rated threshold. Once this link breaks, the curtain blade is released to close the damper. For vertically mounted dampers, the curtain blade will fall over the damper’s opening. For horizontally mounted dampers, the curtain will be driven across the opening by springs. Special latches lock the blade in position. These latches keep the damper closed during a fire event. 

All fire dampers will be rated for static or dynamic air conditions depending on their design. This refers to whether the damper can close against air flow. A dynamic fire damper can close on an air stream even if fans are running (dynamic air conditions). A static fire damper will only close if air flow has stopped (static air conditions). Choosing one over the other will depend on your fans. If your fans stop at the start of a fire, then static fire dampers will work for your system. If fans stay powered, you will need to use dynamic fire dampers.

Fire dampers can be rated for either static or dynamic conditions, but smoke dampers and combination fire-smoke dampers will only be rated for dynamic conditions.

2.) Smoke Dampers

Noxious fumes can spread through your building by infiltrating the ventilation openings in your walls and ceiling. Smoke dampers contain these fumes and prevent them from spreading through your HVAC system.

Smoke dampers are multi-blade dampers that are similar in design to standard control dampers, but with a few key differences. These dampers have seals on the edges of each blade and along the damper's jambs, to prevent smoke from passing through the closed damper.

Each smoke damper will have a smoke detection system tied to the damper’s actuator, to check the air stream for signs of noxious fumes. When smoke is detected, the actuator will receive an electrical signal to close the damper and prevent smoke from spreading further into the HVAC system. Actuators can also be tied to the building’s fire alarm system to close the damper when the alarm triggers.

Every smoke damper undergoes a multitude of tests in accordance with UL 555S, including an air leakage test. Test labs measure air passing through the closed damper at elevated temperatures and across multiple sizes. These measurements are compared to the largest size damper and determine the damper’s Leakage Class, from I to III. The Leakage Class indicates the minimum amount of air allowed through the closed damper at a given air pressure:

• Leakage Class I: 8 cfm/sq.ft. @ 4.5 in. w.g. or 11 cfm/sq.ft. @ 8.5 in. w.g.
• Leakage Class II: 20 cfm/sq.ft. @ 4.5 in. w.g. or 28 cfm/sq.ft. @ 8.5 in. w.g.
• Leakage Class III: 80 cfm/sq.ft. @ 4.5 in. w.g. or 112 cfm/sq.ft. @ 8.5 in. w.g.

Leakage Class I is considered the best classification for smoke dampers because it allows for the least amount of leakage.

Smoke dampers will typically remain closed when noxious fumes are detected in the air stream, but there are times when they may need to open again. First responders will need to access all areas of the building, including those areas filled with smoke and noxious fumes. A smoke control system allows an operator to open and close smoke dampers to redirect smoke into an unoccupied part of the building. From there, they can continue fighting the fire without having to worry about dangerous smoke.

Smoke dampers are a vital part of a passive fire protection system. Together with fire dampers, smoke dampers give first responders precious time to combat fire and give occupants more time to safely leave the building. Each life safety damper is important, but there is a certain type that can protect from both elements.

3.) Combination Fire-Smoke Dampers

Combination fire-smoke dampers perform the task of both fire and smoke dampers. These dampers are rated to block flames from passing through a barrier penetration and prevent smoke from spreading through the HVAC system. Combination fire-smoke dampers will always have multiple blades tied to an actuator. 

The damper’s actuator will be equipped with a heat response device and tied to a smoke detection system, to close when noxious fumes or elevated temperatures are detected near the damper. These dampers are equipped to detect both hazardous elements, fire and smoke.  

Combination fire-smoke dampers must meet UL 555 and UL 555S to be used for both scenarios. Since they meet both standards, you can use combination fire-smoke dampers for fire and smoke requirements. These dampers can be a versatile and cost-effective unit, providing passive fire protection to your building.

4.) Ceiling Radiation Dampers

Ceiling radiation dampers provide a specific kind of protection. As the name implies, these dampers are installed in ceiling penetrations and prevent radiant heat from passing into the concealed space between floors. During a fire, the heat from the flames can radiate into these areas and spark flames.

If a fire breaks out in this space, it will be difficult to extinguish. Worse, a fire between floors will quickly weaken structural members and cause a catastrophic failure. Ceiling radiation dampers prevent the buildup of heat by closing off the penetration during a fire.

The typical ceiling radiation damper consists of two or four wing-style blades that are suspended in the open position with a fusible link. When the fusible link breaks, the blades will come down over the damper opening and seal it off. These blades can be insulated or uninsulated; even uninsulated blades will provide basic protection from radiant heat. Ceiling radiation dampers contain heat and prevent it from sparking fires in the crucial structural points between floors.

Need life safety dampers for your next project? Air Balance offers static and dynamic fire dampers to meet your fire safety requirements. Looking for something else? Contact us by clicking on the button below.

MCDLG & Continuing Education

MCDLG offers free self-paced courses online through AEC Daily. 

Our UL Damper course, Fire & Smoke Protection with Life Safety Dampers, goes over all of the basic stats, terms, and principles involved in choosing life safety dampers for your passive fire protection system.  

This course provides continuing education credits for a variety of institutions, including ASHRAE's PDUs. Learn the basics of UL dampers and earn credit, at your own pace. Visit the MCDLG course page on AECDaily.com today!