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Fiberglass Insulation: Use With Care

By HHI Staff

Fiberglass, also know as 'glass wool', is simply glass that is in the shape of thin threads. Because of their small diameter, fibers of glass are very flexible. However, they can still be broken, and like a broken window, they are capable of cutting the body, although the cuts will be very small.


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Technically, fiberglass is said to be a man-made mineral fiber, as opposed to a naturally occurring mineral fiber like asbestos which is mined directly from the earth. Fiberglass is made by melting glass and drawing it out into strands. Rock wool is another man-made mineral fiber that can be used for insulation. It is made by melting rocks or slag and drawing it into threads. Rock wool is not encountered today as much as fiberglass although it has similar properties.


Fiberglass can be combined with various polyester or epoxy resins to produce fishing rods, skis, sports car bodies and bullet proof vests. The combination of fiberglass and resin can be very strong. The glass tends to reinforce the resin yielding an end product that is considerably stronger than either of the original components. Raw fiberglass can also be woven into fabric for use as products such as draperies. Fiberglass cloth is especially suited for fire resistant applications. In house construction, fiberglass insulation is very widely used. It can be found inside walls, floors and ceilings as well as around furnace ductwork. Another use of fiberglass is in air filters.


During manufacture, fibers can be made into long continuous threads of fairly large diameter, or into shorter, smaller diameter individual strands. The long, large diameter threads are generally used in fabric, and are usually too big to become airborne. Therefore, they cannot be inhaled. They can, however, still cut the skin. The smaller fibers are of a size that can become airborne. As they float through the air, they may be inhaled. While many of these fibers are too large to get past the nose, some of the very small diameter fibers can find their way into the lungs. Fiberglass insulation tends to use smaller fibers because of their enhanced insulating ability.


When fiberglass is combined with a resin to make an object like snow skis, it is trapped in the resin and cannot become airborne. These products are referred to as "reinforced fiberglass" products. The resins used can outgas various fumes that have been shown to bother sensitive people. If such an object is broken, sanded or otherwise abraded, airborne fibers and bits of resin can be released into the air.


Most of the fiberglass that is used for insulation or for air filters has some sort of resin coating. This helps the product hold its shape. Insulations and filters only contain a minimal amount of resin, so fibers can break off and float around the air relatively easily when they are handled. Instead of being simply fiberglass particles, they are resin coated fiberglass particles. Sometimes, fiberglass insulations or fiberglass air filters can contain oils or other materials.


Is Fiberglass Insulation Safe?

According to the American Lung Association, fiberglass insulation is safe when correctly installed.



However, the Lung Association also says: "Direct contact with fiberglass materials or exposure to airborne fiberglass dust may irritate the skin, eyes, nose and throat. Fiberglass can cause itching due to mechanical irritation from the fibers ... Breathing fibers may irritate the airways resulting in coughing and a scratchy throat. Some people are sensitive to the fibers, while others are not."


Changing Views 


•   In 1994, the National Toxicology Program (NTP) indicated that fiberglass was "reasonably anticipated to be a human carcinogen," based on animal data.
•   In 1998, The American Conference of Governmental Industrial Hygienists said 'glass wool' was "carcinogenic in experimental animals at a relatively high dose ... not considered relevant to worker exposures."
•   In 1999, OSHA and fiberglass manufacturers agreed on ways to voluntarily control workplace exposures. The voluntary Health & Safety Partnership Program recommended an exposure level of 1.0 fiber per cubic centimeter (f/cc) based on an 8-hour workday.
•   In 2000, The National Academy of Sciences (NAS) stated that in epidemiological studies of fiberglass manufacturing workers, "glass fibers do not appear to increase the risk of respiratory system cancer."
•   In 2001 The International Agency for Research on Cancer (IARC) working group revised their classification of fiberglass from being a possible carcinogen to not classifiable as a human carcinogen. Studies conducted since the original report show there is not enough evidence to link fiberglass to cancer risk.


Health effects of fiberglass can be related to either the glass fibers themselves or to the resin or oil that coats the fibers. As fibers float through the air, they can pick up an electric charge. Some researchers believe that this may also have an effect on how the fibers react with the body.


Experiments with rats have demonstrated a clear relationship between cancer and fiberglass when the fibers are surgically implanted, but not when they are inhaled. Industry representatives concede that surgical implantation is indeed a cause of cancer, but suggest that the studies showing a relationship between inhaled fibers and factory workers are invalid.

Residential fiberglass batt insulation contains about 5% resin binder that is capable of outgassing formaldehyde fumes into the air. The pink colored insulation manufactured by Owens-Corning Fiberglas Corporation contains, in addition, about 1% dye that has its own outgassing characteristics. The resin used in insulation is usually a phenol-formaldehyde product, but Manville Corporation uses a urea-extended phenol-formaldehyde resin, which outgasses at a faster rate. Of the major insulation manufacturers, the batt insulation produced by Certainteed Corporation, with 4% phenolformaldehyde resin and no dye, is probably the least potent from an outgassing standpoint, however, it can still bother people sensitive to formaldehyde.


When resin coated fiberglass enters the sinuses or the lungs, there is the possibility that the resin could react with the soft tissues and cause inflammation or damage. It is known that formaldehyde based resins decompose when exposed to heat and humidity, yet no research has been done to explore this mode of exposure.


What should you do if your home is insulated with fiberglass insulation? Most researchers don't believe that it presents enough of a problem to warrant removal. In most installations, the insulation will stay where it is placed in the attic, walls or floor and will cause no problems. The tighter the house is constructed, the less likely that any glass fibers or formaldehyde fumes will migrate into the living space.


If health problems are suspected to be related to insulation, the air in the house should be tested by a reputable firm. Removal of the insulation should only be attempted as a last resort because it is messy, costly, and could result in greater contamination of the house. A better solution would be to caulk and tape shut the pathways through which the insulation is entering the living space.


If you are working with fiberglass insulation, it is important to wear protective clothing such as long sleeves and gloves. A dust mask and/or activated charcoal mask is also recommended. Clothing should be laundered separately to avoid contaminating other garments.


In new installations, it is a good idea to totally separate the insulation from the living space. This can be done by sealing all openings in the walls around electrical outlets, windows, etc. Foil-backed drywall can be used to insure that formaldehyde fumes do not migrate into the house. The result may be a house that needs a fan or other mechanical device to introduce fresh air, but this is preferable to breathing glass fibers and fumes outgassed by the resin binder. Uncontrolled infiltration means that air passes through walls, possibly bringing with it resin coated glass fibers.


It is often necessary to insulate heating and air conditioning ducts. In order to avoid contaminating the airstream, this should always be done on the outside of the ducts. It is also a good idea to tape all of the seams in the ductwork prior to adding the insulation so the fibers or formaldehyde fumes cannot enter.


An often overlooked source of indoor air pollution involves fiberglass air filters. Most contain some type of resin or oil that can bother sensitive people. These materials are often added to the fiberglass to enhance its dust grabbing ability. Unfortunately, they can outgas minor amounts of fumes into the fresh air stream. This can be a problem with even the most expensive air filters. While they may be effective in removing dust, their outgassing actually adds other pollutants to the air. For this reason, selecting a tolerable air filter is often a problem for sensitive people.


(Note: The views expressed in this article are those of the author, and do not necessarily represent those of The Healthy House Institute, LLC.)



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HHI is committed to accuracy of content and correcting information that is incomplete or inaccurate. With our broad scope of coverage of healthful indoor environments, and desire to rapidly publish info to benefit the community, mistakes are inevitable. HHI has established an error correction policy to welcome corrections or enhancements to our information. Please help us improve the quality of our content by contacting with corrections or suggestions for improvement. Each contact will receive a respectful reply.

The Healthy House Institute (HHI), a for-profit educational LLC, provides the information on as a free service to the public. The intent is to disseminate accurate, verified and science-based information on creating healthy home environments.


While an effort is made to ensure the quality of the content and credibility of sources listed on this site, HHI provides no warranty - expressed or implied - and assumes no legal liability for the accuracy, completeness, or usefulness of any information, product or process disclosed on or in conjunction with the site. The views and opinions of the authors or originators expressed herein do not necessarily state or reflect those of HHI: its principals, executives, Board members, advisors or affiliates.

Fiberglass Insulation: Use With Care:  Created on March 17th, 2007.  Last Modified on February 28th, 2011


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