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The ABC of dampers

Javed Tejani walks us through the basics of dampers through a easy-to-understand Q&A. He emphatically says that dampers can save lives in the event of a fire.

| | Jul 12, 2012 | 8:11 pm
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Javed Tejani walks us through the basics of dampers through a easy-to-understand Q&A. He emphatically says that dampers can save lives in the event of a fire.

Please describe/define a fire damper, a smoke damper and a combination of both.

A fire damper is a device used to restrict the passage of flame through the ductwork of an air system. A fire damper is installed in a fire-rated wall or floor and closes automatically to maintain the integrity of the partition in case of fire.

A smoke damper, on the other hand, is a device used to restrict the spread of smoke in an HVAC system, which shuts down in the event of fire, or to control the movement of smoke in a building, when the HVAC system is operating in dynamic system.

A combination of smoke fire damper is a device that can be used as a fire damper as well as a smoke damper.

Basically, fire dampers are of two types – manual and motorised. A manual fire damper consists of a bimetallic fuse link. When the temperature reaches a predetermined level, the link will break and the damper will close down.

A motorised fire damper consists of an electro-thermal heat sensor and spring return actuator (motor). When the temperature reaches a certain designed level, the heat sensor will give the signal to the actuator, and the damper will close down.

Smoke dampers are divided according to their leakage class – Class I, Class II and Class III. This class division is according to AMCA 500D table. The bigger the class, more the leakage. Class I and Class II are recommended for HVAC systems.

Please list the advantages and disadvantages of manual and motorised dampers and in what conditions do each work best?

To test a manual damper you have to open the access door and perform the drop test. This is difficult, especially when the damper is installed within a congested space. To test a motorised damper, you just have to push the button and then reset it.

In a manual damper, you have to replace the fuse link, whereas in a motorised damper, the heat sensor is reusable.

Cost-wise, a motorised fire damper is more expensive than a manual damper. But generally speaking, though motorised dampers incur more installation cost, in the long run, they are more effective and easier to commission than manual dampers.

What are the maintenance issues involved?

If the installation of the damper is correct and according to the manufacturer’s instructions, then there will be fewer maintenance issues. Generally, in manual fire dampers, after a period of time, the fusible link could break because of heat and improper handling of the dampers. It is very important to frequently inspect the blade position of the damper and rectify any problems immediately. On motorised dampers, this issue can be solved by pressing the reset button.

What are a few thumb rules for fire damper installation?

All fire dampers have to be installed in the fire wall it is intended to protect, unless the particular fire damper is tested and approved for out-of-the-wall installation. The access door should be installed near the damper so that it will be easier to maintain. It is always recommended to use the fire damper with an auxiliary switch as well as a visual indicator to monitor the damper blade position from outside.

In your opinion, which is more dangerous – the spread of fire or the spread of smoke?

In fire accidents, it is a well-known fact that smoke has taken more lives than the fire itself. In a recent fire incident at the AMRI Hospital in Kolkata in India, it was found that the major casualties were because of suffocation and smoke inhalation.

In any centralised air conditioning system, smoke can be managed by two different systems – the static system and the dynamic system. In a static system, all the units are shut down in case of fire, and the smoke damper closes to prevent the spread of smoke. The static system is generally used in smaller structures like villas or low-rise buildings. In the dynamic system, in case of fire, the movement of smoke is controlled and it uses walls and floors to create the pressure difference. Pressuring the area surrounding the fire prevents the spread of smoke to other areas. The dynamic system is generally used in high-rise buildings.

What needs to be kept in mind while selecting dampers?

Before selecting any damper, one should understand its operation. A fire damper always closes down in case of failure, while a smoke damper and combination of smoke/fire damper can be kept open or closed depending on the requirement and design of the project. While selecting a fire damper, a smoke damper or a combination of smoke and fire damper, one should get it approved by the local civil defence authority and a certifying body like UL, EN or BS.

How important are dampers during an event of fire?

Once again, I cite the example of the AMRI Hospital in Kolkata. The conclusion report stated that had dampers been installed in the duct system, then casualties could have been avoided or minimised.

Do you think there are adequate codes, standards and regulations regarding dampers in the Middle East? Are they at par with international standards like the NFPA?

Once the damper is installed in the HVAC system and the building is handed over to the client, then its maintenance and commissioning needs to take charge. More codes and regulations are needed in this area.

According to the NFPA, it is mandatory that the fire damper is tested a year after installation. But it appears that hardly any contractors or facility management companies follow this.

Javed Tejani is Technical Sales Manager, Prime AC Industries. He can be contacted at: javed.tejani@primeaircon.com

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