Life Safety in HVAC - Ceiling Radiation Dampers

What are ceiling radiation dampers? How do they work? Why are they important for your building? In this article, we will discuss how CRDs (ceiling radiation dampers) fit into the fire response in your HVAC system.

Life Safety in HVAC

Life safety in HVAC consists of multiple layers. Life safety dampers, like fire dampers, are designed to keep occupants safe during a fire event by closing at the first signs of a fire event. They close to prevent the spread of smoke and flames. Smoke dampers keep smoke contained near the source of the fire, so that it doesn’t quickly spread through the HVAC system.

Fire dampers close to prevent flames from passing through HVAC penetrations in a fire barrier. We have covered these two damper types in our series on Life Safety in HVAC, but there are two more to discuss.

The third type of life safety damper is a combination fire-smoke damper, which fulfills both fire and smoke requirements. The fourth type, the ceiling radiation damper, plays an important and specialized role.

What is a ceiling radiation damper?

Ceiling radiation dampers (or CRDs) are small dampers with a straightforward design. They can be round, square, or rectangular depending on the opening they are installed in. These dampers are built for small openings in the ceiling of rooms that share space with the floor above. We will discuss the specifics in more detail later in the article.

Like curtain fire dampers, ceiling radiation dampers stay open during regular operation with a nearly 100% free area. These dampers use a “butterfly blade”. Butterfly blades are raised up and held together by a fusible link during standard operation.

The link is set to break at a predetermined temperature, typically 165 degrees Fahrenheit, which releases each side of the butterfly blade. These sides come down to cover the opening, closing it off.

CRDs can use a two-sided blade or a four-sided blade, depending on the model, but they work the same way. When the fusible link breaks, the blades fall over the opening.

What do they do?

Ceiling radiation dampers prevent heat from radiating into hard-to-reach places. We mentioned earlier that CRDs are installed in ceilings that share space with a higher floor, but they are also installed in any room with a concealed space above the ceiling.

Flames and smoke are the main concerns in a fire event, but there is also the heat generated by the flames. This intense heat will rise to higher floors and could potentially ignite new fires, including in the spaces between each floor. Ceiling radiation dampers prevent the heat from radiating into the spaces above.

The damper’s blades can be insulated or uninsulated, depending on what you need in the room. The goal of CRDs is to keep the heat transfer to a minimum, which is why many prefer insulated blades over uninsulated.

Uninsulated blades can still mitigate radiant heat, thanks to the damper’s design. The metal of the damper’s blades will act as the barrier, slowing the spread of heat into this space. While it doesn't have the same effect as an insulated blade, it is better than having nothing in the opening. Insulated blades will have material embedded in the blade, like gypsum board, that limits heat transfer through the damper.

Where do they go?

CRDs are installed in openings in the ceiling of a room that has a concealed, shared space with the room above. These openings are referred to as “membrane penetrations”, because the opening only penetrate one side of the space. This space can be used to house lighting fixtures or diffusers for the HVAC system. These openings need protection.

Ceiling radiation dampers are installed in the openings above these fixtures, to prevent heat from passing through to the space above. Without CRDs, this space is vulnerable during a fire event.

If a fire starts here, it becomes incredibly difficult to extinguish. And worse, these fires can quickly spread to the floors above and compromise the structure of the room. This puts first responders in danger, on either side of the fire. Ceiling radiation dampers are designed and tested to mitigate this risk.

How are they tested?

Like any life safety damper, CRDs are tested under UL standards for resilience during a fire event. Ceiling radiation dampers are tested under UL Standard 263. This subjects a sample damper to the following tests:

• Fire endurance test will measure a damper’s ability to close and withstand intense heat for a predetermined period. For ceiling radiation dampers, this will be either one or two hours, depending on the ceiling assembly.
• Salt spray exposure test subjects the damper to 120 hours of salt spray to simulate the build-up of dirt and airborne debris, then tests its ability to close and latch.
• Spring closing force tests the force of the springs used to close a static-rated CRD. The closure springs must exert a force of 2½ times that required to close the damper.
• Dynamic closure tests closure of a dynamic-rated CRD against a minimum air velocity and static pressure three times at ambient conditions. Then, the damper must close with its heat response device against airflow at an elevated temperature. These tests are repeated for airflow in the opposite direction.

Failing any one of these tests will mean the damper fails the test. The unit will not be approved for use as a ceiling radiation damper.

Why are they important?

Ceiling radiation dampers help prevent a worst-case scenario during a fire event. As we said before, a fire in this space can be disastrous for first responders and evacuees. It puts them in a situation where the ceiling, or the floor, could collapse on them.

The best way to fight these fires is to prevent them from happening. By installing CRDs, you limit the amount of heat transferred into the space, which reduces the risk of igniting the material in this space.

Life safety dampers contain the spread of fire and smoke to the origin point. They help provide a safe path for occupants to evacuate during a fire event. Building codes and standards will call for life safety dampers at key points throughout your building. Make sure you meet these requirements with the right dampers.

For more on life safety dampers:

• Life Safety in HVAC - What is a Fire Damper?
• The Condenser - Fire Response for Life Safety Dampers
• Fire Damper Sleeves - A Crucial Component

Start your next project with fire dampers by Air Balance. We build dampers for meeting life safety requirements, including passive fire protection and smoke control. Contact Air Balance today and let us help with your next project.