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NTP's Report on Carcinogens Released

The U.S. Department of Health and Human Services released the 12th edition of their "Report on Carcinogens" (ROC) on June 10, 2011. Included among the substances that are "reasonably anticipated to be human carcinogens" are "Certain Glass Wool Fibers (Inhalable)" [1]. According to the Report, "Types of insulation glass wool fibers tested in experimental animals included (Glass Manufacturer's Name Omitted), MMVF 10 and 10a (both of which represent the respirable fraction of (Glass Manufacturer's Name Omitted) 901 glass fiber), MMVF 11 (the respirable fraction of (Glass Manufacturer's Name Omitted) B glass fiber), and unspecified glass wool fibers. Inhalation exposure of F344 rats to (Glass Manufacturer's Name Omitted) FG insulation fiberglass with binder (4 to 6 µm in diameter and > 20 µm long) significantly increased the incidence of mono-nuclear-cell leukemia in rats (males and females combined)."[2]

In their press release announcing the release of the report (, the National Institutes of Environmental Health Sciences elaborated, "Not all glass wool or man-made fibers were found to be carcinogenic. The specific glass wool fibers referred to in this report have been redefined from previous reports on carcinogens to include only those fibers that can enter the respiratory tract, are highly durable, and are biopersistent, meaning they remain in the lungs for long periods of time. Glass wool fibers generally fall into two categories for consumers: low-cost, general purpose fibers, and premium, special purpose fibers. The largest use of general purpose glass wool is for home and building insulation, which appears to be less durable and less biopersistent, and thus less likely to cause cancer in humans."

The National Toxicology Program's Fact Sheet on Certain Glass Wool Fibers (Inhalable)[3] discusses how people are exposed to glass wool fibers; "People are primarily exposed to glass wool fibers by inhaling them in workplaces where products containing glass wool fibers are produced. Individuals working on home improvement projects installing or removing insulation made of glass wool products may also be potentially exposed. However, in general, due to their low durability, most home insulation fibers are less likely to cause cancer in humans."

The ROC describes the manufacture of glass wool insulation as follows; "If the purpose of the fibers is production of home and building insulation products, the newly formed fibers are usually sprayed with a binder, typically phenol-formaldehyde. The finishing process begins with the collection of the fibers within the forming chamber to create a mat on a suction conveyor belt of porous metal in a hood. The fiber mat with binder exits the forming hood via the conveyor carrier through a gas-fired oven, which cures the binder." [4]

The ROC also listed formaldehyde as a known human carcinogen.[5] Describing occupational exposure as "...high variable and...occur(ing) in numerous industries, including the manufacture of formaldehyde and formaldehyde-based resins, wood-composite and furniture production, plastics production, embalming, foundry operations, fiberglass production, construction, agriculture, firefighting, and histology, pathology, and biology laboratories, among others." [6]

Homeowners and workers seeking more information about safe work practices and protective equipment when dealing with glass wool fibers can go to

1: Report on Carcinogens, 12th Edition, 2011, page 207 (Full report available on-line at
2: ibid, pg 208
3: Certain glass Wool Fibers (Inhalable), June 2011, (available on-line at
4: Report on Carcinogens, op. cit., pg 212
5: ibid, pg 195
6: ibid, pg 201

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