Life Safety in HVAC - Combination Fire-Smoke Dampers

Life safety is a crucial part of HVAC. In this article, we will discuss the traits of the combination fire-smoke damper and their role in your HVAC system.

Responds to Fire and Smoke

Life safety dampers are dampers designed for emergency scenarios, specifically building fires. 

Combination fire-smoke dampers will need a heat response device and a smoke detector. 

The goal of these dampers is to contain dangerous elements to certain parts of the building, so that occupants will always have a safe path to evacuate.

Combination fire-smoke dampers respond to the two main signals of a fire event: smoke and intense heat. This damper will have two devices, one to respond to each signal, that close the damper on detection. These two devices are heat response devices (HRDs) and smoke detectors.

Heat response devices react to an intense rise in temperature, in line with the beginnings of a fire event. They can be electronic devices, like the sensotherm. Sensotherms utilize thermosensitive discs that break the electrical circuit to the actuator. Without power, the actuator closes the damper via internal springs.

HRDs can also be simple, like the fusible link. As we’ve explained in a previous article, fusible links hold the damper blades open and break apart under intense heat. These devices give the damper the ability to react.

Smoke detectors are self-explanatory. You can likely see them right now if you look up at the ceiling. We’ve covered their use in HVAC on the Newsstand. To summarize, the smoke detectors used for life safety dampers work in a different way. Instead of sounding an alarm, the detector will send a signal to the damper’s actuator to close.

Smoke detectors are wired to the damper’s actuator so that they can interrupt power when they detect smoke. This triggers the actuator’s “power off” state, which is typically to “spring closed”. 

Fire-smoke dampers will have both devices installed. They must react to either signal.

Fulfilling Both Requirements

Fire-smoke dampers can fulfill both fire safety and smoke safety requirements. This is because each damper must complete both testing standards – UL 555 and UL 555S – to meet both requirements. This makes them an enticing choice for meeting requirements.

UL 555 and UL 555S outline a series of tests for fire dampers and smoke dampers, respectively. These tests determine a damper’s capabilities during an emergency. The damper must complete every test in accordance with UL 555 to determine the damper’s resilience.

For the fire endurance test, the damper is installed in a test oven and subjected to a large fire. The damper must remain intact throughout the test, which can last up to three hours, and then open without issue.

Other fire safety tests include hose stream testing, salt spray testing, cycle testing, duct impact testing, and dynamic closure testing. The last of these tests determines whether the fire damper is rated for dynamic closure. Fire-smoke dampers are always rated for dynamic closure. These tests ensure the damper will remain intact during a fire event, so that it can slow the spread of flames through HVAC openings in a fire barrier.

Smoke dampers undergo similar tests under UL 555S, and in some cases the same tests. For example, smoke dampers must also complete salt spray testing. During temperature degradation testing, the damper is baked in a test oven for 30 minutes.

Manufacturers may choose to test the damper for 250- or 350-degrees Fahrenheit, depending on the desired temperature rating. After the thirty minutes baking process, the smoke damper is removed and cycled three times. The damper must successfully close and open three times to successfully complete the test.

Leakage testing measures the amount of air that passes through the closed damper after it has been subjected to elevated temperatures. The damper will be assigned a leakage class based on the amount of leakage through the closed damper. This class helps gauge the effectiveness of the damper during an emergency.

Smoke dampers are designed to slow the spread of smoke through the HVAC system. They close at the first signs of smoke. That is why each smoke damper must also complete cycle testing, operations testing, fire exposure testing, and an accelerated aging test. 

Fire-smoke dampers must complete all the tests we mentioned above. They must be ready to respond to either signal. Note that every fire-smoke damper has three ratings applied to it: a fire resistance rating, a leakage class rating, and a temperature rating. This means that they have completed all the tests for fire and smoke safety outlined in both UL standards.

Applying Fire-Smoke Dampers

When should you use a fire-smoke damper? You can use them to meet either requirement. However, you may not want to use a combination fire-smoke damper for every requirement.

If you have a fire barrier with HVAC penetrations, then you can use a fire-smoke damper to complete the barrier. However, fire-smoke dampers will be more expensive than fire dampers. The damper will utilize a smoke detector even if it is being used to fulfill a fire requirement. In this example, the damper will close if it detects smoke before heat. The same goes with smoke safety requirements.

Even if the fire-smoke damper is used for a smoke requirement, it will still have a heat response device to react to heat. The damper must react to either signal.

Fire-smoke dampers can be an expensive option, especially if you only need the damper for one requirement. If you only have a need for a fire damper, then use a fire damper. Fire-smoke can still fulfill important roles in your HVAC system. Use these dampers in areas that require both types of protection. Let’s return to the fire barrier from above. Let’s say the duct in this barrier leads to a junction that services other rooms in the building.

You still need to meet the fire safety requirement for the fire barrier, but you should also think about smoke control. A fire-smoke damper would be your best option here. The damper is tested for both scenarios and can react to either signal.

Life Safety in HVAC

It can be difficult to juggle the many requirements involved in designing HVAC systems, but it’s important to always meet the standards for life safety. Your HVAC system plays an important role in fire and smoke safety.

Life safety dampers keep occupants safe during an emergency. Be sure to meet those requirements and protect the most important part of your building: the people inside.

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

• Fire Damper Types and Benefits
• Damper Showdown - Smoke Dampers versus Fire-Smoke Dampers 
• The Condenser - Fire Response for Life Safety Dampers
• The Four Types of UL Life Safety Dampers