The No. 1 question about fire and smoke dampers that mechanical engineers and contractors ask is, “How do the controls work with the actuators?” This article explains that.

DAMPER TYPES

We must clearly distinguish among three types of dampers.

Fire dampers

Fire dampers, which rarely are actuated, close when a rise in temperature occurs and stay shut to stop fire from passing through a barrier. About 90 percent of fire dampers are curtain-type dampers that close when a mechanical fusible link melts, releasing a closing mechanism. A damper must be in the plane of a firewall, although some jurisdictions make exceptions if ducts are heavy duty. Out-of-partition dampers are available from most manufacturers.

PHOTO A. Curtain fire dampers.

In a few cases, auxiliary contacts are needed to prove opening and closing in periodic testing. Dampers with blade switches or actuators with internal auxiliary switches provide proof of closure.

Fire dampers normally close when the temperature of the fusible link reaches 165°F, although some local variations exist. For example, if steam coils are present in ducts, use of a 212°F high limit may be used. The fire-damper temperature then may rise a couple thousand degrees, but the damper will hold for the time rating for which it was designed.

Each year, several million fire dampers are installed in barriers designed to slow the spread of fire (Photo A).

Smoke dampers

Smoke dampers, which are actuated, must open and close when required to provide fresh air or to stop smoke passage. They do not have to have high-limit sensors or fusible links to close automatically. Smoke dampers often provide signaling for indicator lights, as discussed later in this article.

PHOTO B. A smoke damper.

Practices vary by geographical region and by type of smoke control mandated by codes. Most commonly, a smoke detector (or two) inside of ducts will shut down fans and close dampers if smoke is detected. Area smoke detectors sometimes are wired to a central fire-alarm panel, while a panel contact or remote relay initiates closing.

Smoke dampers do not need to be within a wall providing a smoke barrier; they merely need to be within 24 in. of the wall. As a result, the actuators may be axle-shaft mounted. However, most are jackshaft mounted with linkage to the damper blades (Photo B).

Combination fire and smoke dampers

Because combination fire and smoke dampers, which are more common than simple smoke dampers, are fire-rated, their blades must be in a barrier wall. The actuator cannot be in the wall, so a jackshaft and linkage are employed with the actuator connected to the jackshaft extension outside of the damper sleeve. (There are other methods. However, this is standard in the United States.) Almost all current actuators are direct-coupled.