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HVAC duct damage as a source of airborne fiberglass fragments: This document provides information about fiberglass hazards in heating and air conditioning ductwork in residential and light-commercial buildings.

Readers should see Fiberglass Detection in Building Air. Readers should also see FIBERGLASS HAZARDS and also see FIBERGLASS DUCT, RIGID CONSTRUCTION.

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Recognizing Fiberglass Duct Insulation

Fiberglass insulation material appears in several forms in heating and air conditioning systems in both ducts and air handlers themselves. The most common uses of fiberglass insulating material in HVAC systems includes the cases listed below.

The annotated duct system photographs below show the most common types of fiberglass HVAC duct materials. We provide these (C)-protected photographs of fiberglass insulated ducts and HVAC components to aid in recognition of these materials.

Flex Duct using fiberglass insulation

Flex duct with fiberglass insulation sandwiched between a plastic inner and outer wrap. Flex duct may be used for both supply air (shown here at left, poorly installed and crimped) and return air (second photo) in buildings.

The flex duct shown at left is a newly-installed foil-faced flex duct product. The photograph at right shows foil-faced smaller-diameter high-velocity HVAC ducts as well as the main trunk line which has also been covered with foil-faced fiberglass insulation.

The flex duct in these photos shows at left, a clean, newly installed duct line, and at right, the typical debris we observe inside of most duct systems. This debris could have been prevented inside the duct system by better filtration at return air inlets. In a home without mold or allergen or similar indoor air quality complaints, usually we find in the lab that this gray dusty debris is comprised principally of skin cells and fabric fibers.

This photo shows white paint over sprayed into a ceiling supply duct - not to be mistaken for duct contamination, but an indicator of hasty workmanship.

Goodman™ gray flex duct has failed in the first photo above. Owens Corning ValuFlex™ gray flex duct can also show this failure as shown in the second photo where, like the Goodman flex duct, the plastic exterior duct wrap has failed [second photo by Mark Cramer, Tampa Florida].

Rigid rectangular fiberglass duct work

Rigid rectangular fiberglass duct work is visible as the return air plenum in the right of the first photo above. This material is usually used for HVAC trunk lines and a variant of it is often found inside of air handlers (right hand photo).

Fiberglass insulating mats and duct linings

Fiberglass insulating wrap

Fiberglass insulating wrap installed on the outside of metal duct work or air handling equipment is shown in the left photo above.

Building insulation is not designed for use inside of HVAC ducts and lacks the binding resin that is applied to minimize airborne fiberglass particle release into the building. The above-right photo shows home-made air handler and return plenum insulation liner using fiberglass batts, resulting in a higher risk of release of unusual levels of fiberglass into the indoor air of the building.

More examples of damage to ductwork due to physical events or mechanical activity or cleaning are found at DUCT DAMAGE, MECHANICAL.

Round rigid fiberglass HVAC ducts

Rigid round fiberglass duct work is sometimes used for distribution of heated or cooled air through building walls or ceilings. Notice that the fiberglass is fully exposed on the interior of this product, making it impossible to clean and providing a surface which easily traps debris.

Fiberglass insulating mats

Fiberglass insulating mats inside of furnaces and boilers, usually enclosed within a steel jacket surrounding the system but possibly also present within the air handler of furnaces and central air conditioning blowers.

The insulation shown in these photos has been subject to condensate or external leaks, risking a mold contamination problem in the system. In the second or right hand photo fiberglass materials have been used inside the air handler sides and top in a foil-faced form (unlikely to release many fibers into the duct system) and a binder-coated mat on the air handler bottom.

Questions & Answers regarding this article

Questions & answers about possible sources of small fiberglass fragments found in indoor air & dust samples.

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  Recognizing Fiberglass Duct Insulation

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
• Environmental Health & Investigation Bibliography - our technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
• Adkins and Adkins Dictionary of Roman Religion discusses Robigus, the Roman god of crop protection and the legendary progenitor of wheat rust fungus.
• Kansas State University, department of plant pathology, extension plant pathology web page on wheat rust fungus: see http://www.oznet.ksu.edu/path-ext/factSheets/Wheat/Wheat%20Leaf%20Rust.asp
• "A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
• US EPA - Mold Remediation in Schools and Commercial Building [ copy on file as /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
• US EPA - Una Breva Guia a Moho - Hongo [on file as /sickhouse/EPA_Moho_Guia_sp.pdf - - en Espanol

Fiberglass in buildings: hazards, testing, cleanup, prevention: references & products

For more information about fiberglass as an indoor air quality concern see:

• Asbestos: How to find and recognize asbestos in buildings - visual inspection methods, list of common asbestos-containing materials (Asbestos is not fiberglass and vice versa).
• BASEMENT MOLD includes examples of moldy fiberglass insulation found in basements
• CRAWLSPACE MOLD includes additional examples of moldy fiberglass insulation found in crawl spaces
• Duct System Defects
• Fiberglass in Indoor Air, HVAC ducts, and Building Insulation, Indoor Air Quality Investigations, building insulation and HVAC duct work insulation hazards
• FIBERGLASS HAZARDS
• Fiberglass Particle Identification in the Fiberglass Test Laboratory
• Fiberglass References - Government Agencies & Authorities list of public documents on fiberglass
• Goodman Gray Flex Duct Deterioration and Failures
• INSULATION INSPECTION & IMPROVEMENT
• Insulation Identification Photographs - Fiberglass insulation photos, yellow, pink, green, white fiberglass identification in building attics, walls, ducts, other locations
• Insulation Identification Photographs - Cellulose insulation photos, Mineral wool insulation photos, rock wool insulation photos, cotton insulation photos, balsam wool insulation photos
• Insulation Identification Photographs - Vermiculite insulation photos
• Lab Identification of Fiberglass photographs and text assist in laboratory identification of fiberglass fibers and fragments in air, dust, or material samples in the laboratory using forensic microscopic techniques.
• Mold in Fiberglass building insulation, when, why, and how fiberglass becomes a reservoir of problem mold in buildings.
• AIR FILTERS, OPTIMUM INDOOR
• Owens Corning Flex Duct Deterioration and Failures
• World Trade Center Dust Particle Identification
• Fiberglass carcinogenicity: "Glass Wool Fibers Expert Panel Report, Part B - Recommendation for Listing Status for Glass Wool Fibers and Scientific Justification for the Recommendation", The Report on Carcinogens (RoC) expert panel for glass wool fibers exposures met at the Sheraton Chapel Hill Hotel, Chapel Hill, North Carolina on June 9-10, 2009, to peer review the draft background document on glass wool fibers exposures and make a recommendation for listing status in the 12th Edition of the RoC. The National Institute of Environmental Health Sciences is one of the National Institutes of Health within the U.S. Department of Health and Human Services. The National Toxicology Program is headquartered on the NIEHS campus in Research Triangle Park, NC. The National Institute of Environmental Health Sciences is one of the National Institutes of Health within the U.S. Department of Health and Human Services. The National Toxicology Program is headquartered on the NIEHS campus in Research Triangle Park, NC.
  Following a discussion of the body of knowledge, the expert panel reviewed the RoC listing criteria and made its recommendation. The expert panel recommended by a vote of 8 yes/0 no that glass wool fibers, with the exception of special fibers of concern (characterized physically below), should not be classified either as known to be a human carcinogen or reasonably anticipated to be a human carcinogen. The expert panel also recommended by a vote of 7 yes/0 no/1 abstention, based on sufficient evidence of carcinogenicity in well-conducted animal inhalation studies, that special-purpose glass fibers with the physical characteristics as follows longer, thinner, less soluble fibers (for 1 example, > 15 μm length with a kdis of < 100 ng/cm2/h) are reasonably anticipated to be a human carcinogen for the listing status in the RoC. The major considerations discussed that led the panel to its recommendation include the observations of tumors in multiple species of animals (rats and hamsters). Both inhalation and intraperitoneal routes of exposure produced tumors, although inhalation was considered more relevant for humans.
• Fiberglass insulation mold: occurrence of mold contamination in fiberglass insulation can be impossible to see with the naked eye, but can be significant
• World Health Organization International Agency for Research on Cancer - IARC Monographs on the Evaluation of Carcinogenic Risks to Humans - VOL 81 Man-Made Vitreous Fibers, 2002, IARCPress, Lyon France, pi-ii-cover-isbn.qxd 06/12/02 14:15 Page i - World Health Organization, 1/21/1998. - Fiberglass insulation is an example of what IARC refers to as man made vitreous fiber - inorganic fibers made primarily from glass, rock, minerals, slag, and processed inorganic oxides. This article provides enormous detail about fiberglass and other vitreous fibers, and includes fiberglass exposure data.
• http://monographs.iarc.fr/ENG/Monographs/vol81/mono81.pdf - the article (large PDF over 6MB)
  http://monographs.iarc.fr/ENG/Monographs/vol81/mono81-6A.pdf - article details
  http://monographs.iarc.fr/ENG/Monographs/vol81/mono81-6C.pdf - studies of cancer in experimental animals in re vitreous fibers such as fiberglass;
  http://monographs.iarc.fr/ENG/Monographs/vol81/mono81-6E.pdf - summary of data reported & evaluation
  http://monographs.iarc.fr/ENG/Monographs/vol81/mono81-6F.pdf for the article references
  To search the IARC monographs on various environmental concerns and carcinogens, use http://monographs.iarc.fr/ENG/Monographs/PDFs/index.php
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