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Asbestos fabrics are found in buildings at a variety of locations including as HVAC duct vibration dampeners, duct or pipe insulating wrap, electrical wire insulation, and in special applications as fireproof curtains or blankets. Here we give sepcial attention to asbestos cloth fabric HVAC duct vibration dampeners or "vibration dampers":
This article describes the vibration damper (vibration dampener or vibration isolator) connecting the air handler unit supply plenum to the building supply duct and cites cases of asbestos-containing air conditioning or heating duct work that could send asbestos fibers into building air.
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Asbestos in or on HVAC ducts (air ducts or heating and cooling ductwork) is a possible hazard for which we provide links to a separate document - see ASBESTOS AIR DUCTS and for a more general guide to recognizing asbestos in buildings, see IDENTIFICATION of ASBESTOS in buildings. Also see NOISE / SOUND DIAGNOSIS & CURE.
The "vibration damper" [properly called "vibration dampener"] shown in this photograph and at the top of this page is a fabric or rubberized fabric flexible connection used to join the supply air plenum to supply ducts in a building.
On a vertical air handler with conditioned air leaving at the top of the unit, you may see this fabric joint at the supply plenum to which the building supply ducts are connected.
The purpose of the vibration dampener is simple: by providing a flexible link between the air handler itself (a possible source of noisy vibrations) and the building duct work, the installer is reducing the transmission of noise through metal ductwork into the rest of the building when the blower, furnace, or air conditioner are running.
Thanks to reader Kenneth Meichtry, Building Maintenance Superintendent at General Services Agency, San Luis Obispo County, CA,for pointing out that the correct term for the HVAC component we illustrate here is vibration dampener.
A vibration dampener is a device designed to absorb rather than transmit vibration. In the case of heating furnaces and air conditioners, mechanical vibrations that occur in the air handler would be transmitted as annoying sounds throughout the building if a vibration dampener were not installed between the air handler unit itself and the metal ductwork to which it is connected.
It would be equally accurate and more descriptive to refer to this device as a vibration isolator since what it's doing is isolating vibration in the vibrating part to avoid transmitting the vibration and thus annoying noise to other parts of the HVAC system or into the building.
On an air handler system or "blower unit", a fabric, currently often made of rubberized material, is installed as the vibration dampener. Vibrations in the air handler move the fabric without being transmitted into the metal ductwork.
In these articles we may include the less correct term "vibration damper" because it is very widely used among HVAC trades workers and because we want online searches for this noise-reducing component to enable our article to be found using either term: vibration damper or vibration dampener.
An additional HVAC noise source is of course an absent vibration dampener or one that is improperly connected or constructed. For example we observed an air handler connection to the supply duct trunk that had so little clearance space between the steel components that even though a vibration dampener had been squashed into that space, vibration and noise from the air handler was being transmitted to the duct system and into the building.
Asbestos & Other Defects in Air Handlers & Duct Work: Damaged Vibration Dampeners & More Air Handler Noises
Inspect the vibration dampener to see that it is intact, not torn or damaged. If the blower is running you may feel air leakage around the damper if it is damaged or not properly installed.
Note that air blowing out of leaks in the HVAC supply duct system as well as air blowing into leaks in the return duct system can be a source of noises in the system including hisses, whistles, etc.
Asbestos Fabric in HVAC Ducts as Vibration Dampener Material
On older furnaces and some air conditioning systems you may see a white woven fabric used for the vibration damper material. It is possible that this material was made of asbestos fabric [better photos wanted].
Colors of asbestos vibration dampener cloth: If the vibration damper fabric is white or white-gray (un-coated asbestos fabric) or possibly silver (aluminized coated asbestos fabric) and woven of a coarse-woven fabric it may be an asbestos material, typically containing chrysotile asbestos fibers in a high percentage.
Look at the lower left corner of our close up photo of a silver-colored asbestos vibration damper at a warm air furnace (photo above right). See that little black round spot above the "D" in "Daniel" of our © notice?
That's where a technician has made a hole in the asbestos damper material in order to insert a thermometer to sense air temperature. The fibers released by such minor damage are probably below the limits of detection.
It is easy to distinguish asbestos fabric in the vibration dampener from other common damper materials which have been used as other fabrics are more finely woven (see photos on this page) and may be rubberized or coated canvas or on newer systems, vinyl-coated synthetic fabric.
Reports of actual asbestos lab tests of asbestos cloth vibration dampers confirms their composition:
The photograph of an asbestos cloth HVAC duct vibration damper shown at left, courtesy Jason Lee, was confirmed by Mr. Lee as containing 65% chrysotile asbestos.
OPINION-DF: Further testing or inspection may be in order, since if indeed asbestos material was used at this location, and especially if it is damaged, it could release asbestos fibers into building air. Do not tear, cut, or damage the material during your inspection.
If the vibration damper is missing, torn, leaky, or is made of asbestos, we recommend that it be replaced with modern materials. In some cases it may be less costly to simply replace an asbestos-suspect vibration damper than to pay to have it tested.
However if you want to test the vibration damper fabric, look inside the return plenum to the inside of the fabric.
Often we can find an individual thread sticking up above the metal clamp securing the fabric to the metal plenum sides, easily clipped with no damage to the fabric itself.
Asbestos Fabric as Duct or Pipe Insulation
Our photograph at above- left illustrates use of an asbestos textile as a duct wrap or pipe wrap. Also see ASBESTOS TEXTILES.
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