Your Questions About Life-Safety Dampers Answered

Life-safety dampers (right, photograph courtesy of Greenheck) prevent the spread of flames and/or smoke during a fire event, facilitating occupant evacuation. Credit: Wittybear/Shutterstock

Application

What is the difference between static and dynamic fire-rated dampers? Static fire-rated dampers are installed in HVAC systems intended to shut down during a fire. Triggered by a smoke detector, an alarm, or a localized increase in temperature, they are designed to close automatically, prohibiting the passage of air through ducts, when fire is detected. Dynamic fire-rated dampers are used in HVAC systems intended to remain operational during a fire. They are designed to operate under airflow and static pressure and to close when the temperature reaches a certain threshold.

When do I use a 1.5-hour fire damper, and when do I use a 3-hour fire damper? NFPA (National Fire Protection Association) 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems, states penetrations in barriers rated for less than 3 hours must be protected with fire or combination fire/smoke dampers rated for 1.5 hours. Penetrations in barriers rated for 3 hours or more must be protected with fire or combination fire/smoke dampers rated for 3 hours.

Does the penetration for a fire damper in a fire-rated wall need to be framed? Yes. All metal- and wood-framed fire-rated walls have framing requirements for openings in which a fire damper or a combination fire/smoke damper is to be installed (Photo A). Manufacturer installation instructions shipped with dampers and usually available online show or have a link to standard framing details.

PHOTO A. Framing of an opening in a fire-rated wall. Photograph courtesy of TAMCO

Which type of heat-responsive device should I use, a fusible link or a thermostat? Fusible links typically are found on curtain and multiblade fire dampers, while thermostats mostly are found on combination fire/smoke dampers.

Single-use devices, fusible links consist of two strips of metal soldered together (Photo B). When the solder reaches a specific temperature (typically, 165°F [74°C] or 212°F [100°C]), it melts, and the two strips of metal separate, enabling a damper to close.

A thermostat (Photo C) is a bimetal thermal disc designed to cut power to an electric damper actuator when a specific air temperature (typically, 165°F [74°C], 212°F [100°C], 250°F [121°C], or 350°F [177°C]) is reached. Many thermostats can be reset in the field once a damper has been inspected and found to be free of damage.

Do building codes explain how to install fire, smoke, and combination fire/smoke dampers? Model codes refer to manufacturer installation instructions and damper listings. Though many manufacturers’ installation instructions are similar, the differences, however slight, may be important. Therefore, be sure to review the instructions for the specific damper to be installed.

How do I know whether I need a smoke damper with a leakage rating of Class I or one with a leakage rating of Class II? Consult your local codes for leakage requirements. If your local codes do not specify a minimum leakage for your application, then refer to the national codes.

For most applications, a minimum leakage rating of Class II is required. Class II leakage means a damper was tested and is approved to leak less than 20 cfm per square foot at 4.0 in. wg (102 l/s/m2 at 1.0 kPa).

For applications such as hospitals, schools, and stairwells, a leakage rating of Class I is required. Class I leakage means a damper was tested and is approved to leak less than 8 cfm per square foot at 4.0 in. wg (40 l/s/m2 at 1.0 kPa).

If a leakage rating is not specified, the designer will need to determine how tight a penetration should be sealed during a fire event.

Design/Installation/Controls

How do you replace an old pneumatic actuator with a new electric model? Locate the damper’s control shaft. If the pneumatic actuator is mounted externally (Photo D), the simplest solution would be a direct-coupled, modern fire/smoke-rated electric actuator. Remove the existing pneumatic actuator and all of the linkages connecting it to the control shaft. Next, place a properly sized direct-drive fire/smoke-rated electric actuator over the drive shaft. If the existing mounting bracket is not long enough to support the anti-rotation strap of the electric actuator, a new mounting bracket will be needed. Make sure the electric actuator is oriented so that it will correctly power-open and, upon the loss of power, spring-close the damper.

If an old pneumatic actuator is internally mounted or connected via a system of linkages, a new linkage and/or mounting plate is/are likely to be needed. Any negator springs used to close a damper likely will need to be removed and/or replaced. Where a swivel, crank arm, and rod are used, a new electric actuator supplied with a built-in crank arm and mounting bracket will be required.

With the new electric actuator (and, if required, linkages) in place, open the damper by hand and power open the actuator. When both the damper and actuator are fully open, connect the actuator to the drive shaft. Next, disconnect power going to the damper and inspect that the damper has fully closed. Lastly, cycle the damper electrically—open and then closed—to ensure proper operation.

Typically, replacing a pneumatic actuator with an electric one is easy. In about 10 percent of cases, however, some investigation and modification is needed. Communication with the damper manufacturer is important to ensuring torque requirements for the damper model and size, airflow conditions, and actuator location are met.

Electro-pneumatic (E/P) switches typically need to be replaced with a relay. Air valves (Figure 1) require new electric thermostat-type heat-responsive devices. Fusible links and shaft springs generally can be retained, with no changes needed.

Does changing out an actuator affect a damper’s UL 555S, Smoke Dampers, certification? Actuator field replacement is outside the scope of UL 555S certification. UL suggests it be done in accordance with the damper manufacturer’s normal field-servicing program. Ultimately, then, it is up to the local authority having jurisdiction (AHJ) to determine if an actuator replacement is sufficient. At the building owner’s expense, a representative of UL can be hired to visit a job site and inspect.

What does the “8-13 psi” on my pneumatic actuator mean? That is the air pressure in pounds per square inch (psi) required for the actuator’s shaft to move fully without a load. In other words, 8 psi is required for the shaft to begin to move, and 13 psi is required for it to fully extend without being connected to the damper. In the same manor, an 8-13-psi spring produces the force required to close the damper. A spring with a different psi range can be used to produce more or less torque.

PHOTO B. Fusible links. Photograph courtesy of TAMCO

PHOTO C. Thermostat wiring box with reset button. Photograph courtesy of Pottorff

PHOTO D. Typical external actuator installation. The electric actuator is direct-coupled to the damper shaft, while the old mounting plate serves as an anti-rotation strap.

FIGURE 1. Pneumatic air valve with fusible-link release.

Can mounting angles be field-supplied? Mounting angles (Photo E) can be field- or factory-supplied. Consult the damper manufacturer’s installation instructions for details.

What is the minimum size and thickness of mounting angles? Minimum size and thickness can vary by manufacturer. Typically, the minimum size is 1.5 in. by 1.5 in. (38 mm by 38 mm). For dampers up to 36 in. (914 mm) wide and 24 in. (610 mm) high, the minimum thickness is 16 gauge. For larger dampers, the minimum thickness is 14 gauge.

When do you use one-sided mounting angles in lieu of two-sided mounting angles? You use one-sided mounting angles when one side of a rated wall is difficult to access or inaccessible.

Is a one-sided mounting angle better than a two-sided mounting angle? Both one-sided and two-sided mounting angles are tested and approved by UL. One-sided mounting angles can be more economical to purchase and install, but typically have more restrictions in terms of size and hourly ratings, the limitations varying by manufacturer.

PHOTO E. Mounting angles. Photograph courtesy of TAMCO

Do I have to seal/caulk mounting angles? The sealing/caulking of mounting angles to a wall or floor is required neither by national codes nor for fire-damper approval. See the damper manufacturer’s installation instructions for approved sealants or firestop material, should local codes require sealing.

How much space between a mounting angle and a damper is allowed? A mounting angle should sit flush against a damper sleeve/frame. Normally, a gap of no more than 1/8 in. (3.2 mm) is acceptable.

Standards and Listings

How do I know if my damper’s ratings are current and correct per the submittal? Per UL requirements, the damper should bear a label indicating the maximum static pressure and airflow the damper is approved to open and close under. Additionally, you can search UL’s UL Product iQ website. The minimum airflow and static pressure for a UL 555S listing is 2,000 fpm (10.2 m/s) and 4.0 in. wg (1 kPa) at 250°F (121°C).

Inspection and Testing

How do you test auxiliary switches on fire dampers (actuator-driven only), smoke dampers, combination fire/smoke dampers, and actuators? Make sure the switch package is not connected to anything. With the damper closed, check for continuity across the switches to determine the closed wiring. Next, power the damper open and check for continuity across the other set of wires. The most common containment-damper wiring is shown in Figure 2.

How do you remotely test actuator-controlled fire, smoke, and combination fire/smoke dampers? Manufacturers provide a number of different configurations of panels, with options such as keyed switches, momentary switches, and selector switches. All use the same concept shown in Figure 3.

When a damper is open, a green light or light-emitting diode (LED) on the test panel will be on. Activating the test switch will cut power to the actuator and, thus, close the damper. Once the damper is closed, the green light or LED should be off, and a red light or LED should be on. Deactivating the test switch will restore the power, and the green light or LED should be on again. The test then is finished. Following installation, damper-blade position should be visually inspected to confirm the wiring and switches are correct and operational.

Alternately, a fire-alarm or building-automation-system module can take the place of a remote-test panel and allow testing from a central control panel (Figure 4).

Conclusion

Restricting the spread of flame and smoke in the event of a building fire, life-safety dampers play a critical role in the protection of people and property. Considering the stakes, it is imperative for buildings professionals to pay attention to details and understand the finer points of the devices’ application, installation, and maintenance.

About the Authors

Dane Carey is director of engineering for TAMCO; James Carlin is product manager, dampers, for Pottorff; Larry Felker is manager, product management, fire and smoke, for Belimo Americas; and Kent Maune is senior product manager for United Enertech.

FIGURE 2. Common containment-damper wiring.

FIGURE 3. Test panel with combination fire/smoke damper.

FIGURE 4. Remote testing of a damper via BACnet.