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Asbestos in Ductwork

Asbestos is unfortunately very common in homes built before the 1970s. Common asbestos-containing materials are floor tiles, pipe insulation, wall materials, ceiling tiles, and thermal insulation. Many of these materials, if they are in good condition, can remain in place if not disturbed. A problematic place where asbestos can be found is on or inside the ductwork. In this blog we will discuss asbestos duct insulation and what should be done about.

Basics of Asbestos Duct Insulation

Asbestos duct insulation is a friable asbestos material which was used to insulate the exterior of duct or the interior near the return, or more commonly found it its tape.. Friable materials are materials that can be ground into a powder with hand pressure while dry. These materials are higher risk because they are more likely to release fibers than their non-friable counterparts. Some examples of what can lead to a disturbance in these materials are construction or renovation work, improper handling of the materials, or excessive vibration and air flow. Common asbestos duct insulation appears to be a white to gray paper-like material that is on (or in rarer cases inside) the duct work. Insulation inside of the duct work is often difficult to find as it usually involves removing the HVAC register supply or return grills to view it. 

Transite Ductwork

Another example of asbestos present in ductwork is transite. Transite is a material that is a mixture of concrete and asbestos. It is commonly also found on the exteriors of garages, sheds, or industrial structures. It is also a material that has one of the highest concentrations of asbestos found in building materials. Transite is considered to be a non-friable material due to its durability. In my field experience, I have commonly seen transite duct worked inside the concrete slab of the property. This is problematic as the transite can break or degrade over time, possibly releasing asbestos fibers. 

Other Asbestos Duct Insulation

In a previous blog, I referenced a “horror story” in which raw asbestos fibers were observed inside of the duct, which became apparent after construction work caused the material to become airborne and scatter its dust across the property. To this day, I am unclear of what classification this insulation was, but it did contain over 20% anthophyllite asbestos,which is rarer than the more common chrysotile asbestos. 

How to Handle Asbestos Ductwork

If asbestos is found inside or around ductwork, what is the solution? The answer is actually quite difficult. If asbestos is found around duct work it can be easily abated and in some cases encapsulated. In other cases if asbestos is inside of the ductwork or literally comprises the duct, in the case with transite, the solution is much more difficult to find. In my experience with asbestos contractors, I have heard recommendations of removing the ductwork completely, to encapsulating transite, to partial removals. It all depends on the extent and condition of the asbestos along with the financial costs of those services. If you suspect you have asbestos duct insulation, have it tested by a licensed asbestos professional such as Indoor Science.

Ian Cull

Ian Cull

Ian Cull is a nationally recognized expert in the field of indoor air quality. He is the Chief Science Officer of Indoor Science, a company he started in 2004. He speaks around the world on air quality topics and is a training provider of the Indoor Air Quality Association. Mr. Cull is a Licensed Professional Engineer (PE) and Certified Industrial Hygienist (CIH). His degree is in Environmental Engineering from the University of Illinois - Urbana Champaign. Mr. Cull has developed 50 air quality related courses for the IAQA University and is the author of the book, “Fundamentals of Mold Remediation”. In his words… “Besides being passionate about indoor air quality, I enjoy cycling, music, the Chicago Bulls, and having fun with my three kids.”