Life Safety in HVAC - What are Smoke Dampers?

What are smoke dampers? Learn how these life safety dampers keep occupants safe during an emergency. Stay informed with the MCDLG Newsstand.

HVAC systems need dampers. There will be several types of dampers throughout the system, all performing distinct roles to meet the building’s airflow requirements. Life safety dampers meet fire safety requirements.

In HVAC, the term “life safety” refers to dampers used in passive fire protection: fire dampers, smoke dampers, combination fire-smoke dampers, and ceiling radiation dampers. These damper types are designed to close at the first signs of danger. Instant action is vital in fire response.

Life safety dampers contain the spread of flames and smoke, so that occupants have a clear path to leave the building. Your HVAC system plays a significant role in fire safety.

What are Smoke Dampers?

Smoke dampers are life safety dampers built to hinder the spread of smoke through ductwork. Smoke can quickly spread through vents and ductwork, if left unchecked. System fans can carry the smoke from its origin point to anywhere in the building.

Many overlook the statistic, but most deaths from fire are caused by smoke inhalation. 

Smoke dampers close at the first signs of smoke or noxious fumes. They can be reopened under certain conditions, to help with smoke evacuation, but otherwise they will remain closed until the fire event has ended. We will discuss the role of dampers in smoke control systems later in this article.

These dampers are typically installed in corridors and walls, and in smoke barriers throughout the HVAC system. Building codes will dictate where smoke dampers should be installed in your system.

Check with local codes and requirements before selecting dampers for your system.

Looking to meet fire safety requirements? Consider adding combination fire smoke dampers from Air Balance. We build every damper to meet your needs. Starting a new project? Contact us today and let's meet your requirements together.

Smoke Detection

Like fire dampers, smoke dampers remain open during regular operation. Each smoke damper will have an HVAC smoke detector tied to its actuator. When the smoke detector senses smoke or noxious fumes, it will send a signal to the actuator to close the damper. The damper will remain closed until it receives a signal to reopen.

There are two types of smoke detectors for HVAC: flow and no-flow. For a full breakdown of these types, check out our article on HVAC smoke detectors.

On the left is a flow smoke detector with sampling tubes in the airstream. On the right is a no-flow detector.

Flow detectors utilize sampling tubes inside the damper that monitor the airstream for smoke. This sampling tube will usually sit behind the damper’s open blades, so that it can sample airflow as it passes through the open damper. Flow detectors need moving air to accurately sense incoming smoke. This can create an issue if there is no air flowing through the duct.

No-flow detectors resemble household smoke detectors and use a similar mechanism to sense smoke: a photovoltaic sensor. This sensor can detect the presence of smoke plumes inside the duct. No-flow detectors are typically installed inside the body of the damper, so that they can monitor the air inside the duct.

This can obstruct airflow during regular operation, but the important trait will be reacting to smoke. The smoke detector must be ready to signal the actuator at the first signs of smoke. The damper needs to close quickly.

Smoke Damper Testing

Smoke dampers must close at the first signs of smoke. Each smoke damper is tested under intense testing established under UL 555S to ensure it will operate in an emergency. UL 555S is the industry standard for smoke damper testing.

Every smoke damper must undergo a series of tests conducted in accordance with UL standards, including cycle testing, smoke leakage testing, and temperature degradation testing. Dampers that complete these tests receive a leakage rating and a temperature rating that corresponds with the completed tests. The damper must safely close when air heats up in the duct.

The temperature rating refers to a temperature degradation test, in which a sample damper is placed in an industrial oven set to either 250 degree or 350 degrees Fahrenheit. The damper will stay in the oven for 30 minutes.

This test determines whether the damper can operate under intense heat. Smoke dampers are not fire resistant, but they will need to operate while subjected to super-heated airflow.

Once the “baking” process is done, the damper is removed and cycled three times. In other words, the damper must fully open and close three times while heated to the designated temperature. Testers will also be looking to the damper’s seals for signs of degradation. This is important for the next set of tests.

Before leakage testing, the sample damper is cycled three more times while subjected to heated airflow. On the third successful closure, testers will measure air leakage through the closed damper blades.

For Leakage Class I, the damper’s leakage must not exceed 8 cfm per square foot at 4.5 in. w.g. of pressure, or 11 cfm per square foot at 8 in. w.g. of pressure. This limit increases to 20 cfm per square foot at 4.5 in. w.g. for Leakage Class II.

There is a Leakage Class III for smoke dampers, which allows for leakage up to 80 cfm per square foot. Most requirements will call for Leakage Class I or Class II, as they allow for significantly less leakage. 

Each test looks for these two key factors in the smoke damper’s design:

• The damper’s ability to operate under elevated temperatures caused by a fire event.
• The damper’s ability to block smoke while closed and subjected to intense heat.

Manufacturers will usually list the smoke damper’s temperature rating and leakage rating on their website. Check the damper’s submittal for additional information.

Smoke Control

Once first responders arrive, the role of smoke dampers can change from containment to flow control. With the right equipment, operators can utilize smoke dampers and fans to vent smoke from area of the system to another.

And with smoke evacuation penthouses, smoke dampers can help vent smoke out of the building through ventilation points in the roof. These penthouses are especially useful for evacuating smoke from elevator shafts. Smoke control helps firefighters access areas that are otherwise overrun with smoke, so that they can safely combat the fire. Smoke control systems are a helpful tool for first responders.

The Purpose of Smoke Dampers

Smoke dampers contain the spread of smoke through your HVAC system. They are designed and tested to withstand the hazardous conditions that accompany smoke and noxious fumes. Your project will require smoke dampers installed at key points in the HVAC system and may also call for specific leakage classes and temperature ratings.

Always check the submittals for a complete list of standards. Make sure each smoke damper meets the needs of your project.

For more on life safety dampers, check out these Newsstand articles:

• The Four Types of Life Safety Dampers
• The Condenser - Fire Response for Life Safety Dampers
• The Condenser - HVAC Smoke Detectors, Flow and No-Flow
• Passive Fire Protection for HVAC