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  • Fiberglass is one of the most widely used insulating materials in the world, despite concerns that it may cause cancer
  • The National Toxicology Program first ruled that fiberglass is “reasonably anticipated to be a human carcinogen,” then revised the ruling to include only certain glass wool fibers (those that are inhalable), which excludes fiberglass;
  • Consumer groups are challenging the revised label, claiming the formula the EPA and NIH used to determine carcinogenicity diluted the results, making them look like fiberglass is safe when it really isn’t
  • Animal studies have shown that certain glass fibers can cause tumors in animals’ lungs and other tissue sites, while cell studies have shown that certain fiberglass fibers may cause damage to DNA
  • When working with fiberglass, choose only formaldehyde-free varieties and wear protective clothing and a respirator; even better, opt for non-toxic insulation materials made from sheep’s wool, recycled blue jeans, newspapers or other natural materials

Is the Fiberglass in Your Attic or Walls Causing Cancer?

April 30, 2012 | 80,965 views
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By Dr. Mercola

Fiberglass, also known as fibrous glass or glass wool, is a man-made fiber used to insulate homes, furnace filters, pipes, appliances and more; it’s also used for sound control in airplanes and automobiles, and in certain curtains, roofing material and plastics.

As its name implies, the main substance in fiberglass is glass, which is finely spun to form a mass that resembles wool.

When working with or installing this material, the small fibers can be swallowed or inhaled, where they may remain in your lungs for long periods of time, potentially leading to health problems like cancer.

Since fiberglass first entered the market in the 1930s, it is now among the most widely used insulating materials in the world, which is why concerns that it may cause cancer need to be taken seriously.

U.S. Government Says Fiberglass is “Reasonably Anticipated” to Cause Cancer – Then Changes its Mind?

Animal studies have shown that certain glass fibers can cause tumors in animals’ lungs and other tissue sites, while cell studies have shown that certain fiberglass fibers may cause damage to DNA. Fiberglass was nominated as a top safety concern on the synthetic mineral fiber list for the Occupational Health and Safety Administration (OSHA) back in 1994. At that time, it was listed as “reasonably expected to be a human carcinogen" by the National Toxicology Program (NTP). However, in 2011, the updated NTP “Report on Carcinogens”i noted:ii

Certain glass wool fibers (inhalable) are reasonably anticipated to be human carcinogens based on

  1. sufficient evidence of carcinoge­nicity from studies in experimental animals of inhalable glass wool fibers as a class … and
  2. (2) evidence from studies of fi­ber properties which indicates that only certain fibers within this class — specifically, fibers that are biopersistent in the lung or tracheo­bronchial region — are reasonably anticipated to be human carcino­gens.”

What is important about this wording is the term “certain glass wool fibers (inhalable),” which by definition excludes fiberglass from receiving a carcinogenic listing. NTP explains this by saying that fiberglass is less durable and therefore less likely to remain in your lungs when inhaled, as compared to other types of glass fibers used for “special purposes” like aircrafts:iii

There are generally two categories of glass wool fibers that consumers might use: low-cost general-purpose fibers and premium special-purpose fibers. Most home and building insulation projects use general-purpose glass wool. Special-purpose glass fibers are used for applications, such as separating the negative and positive plates in a battery, and in high-efficiency air filters and aircraft, spacecraft, and acoustical insulation.

In general, insulation fibers are less durable and less biopersistent than special-purpose fibers, and may be less likely to cause cancer than the more durable, more persistent special-purpose fibers.”

Why Was Fiberglass Removed from the Cancer List?

By removing fiberglass from the “reasonably anticipated to cause cancer” list, OSHA doesn’t list it as a problem for workers, which means dangerous exposures may continue to occur, particularly in factories where fiberglass products are produced or worked with on a daily basis. One consumer group, the National Association of Clean Air Agencies, is protesting the findings, pointing out that the formula the U.S. Environmental Protection Agency (EPA) and NIH used to determine carcinogenicity diluted the results, making them look like fiberglass is safe when it really isn’t. Two problems they noted in a report to the EPA are as follows:iv

NACAA recommends that EPA consider potential or allowable emissions, rather than actual emissions, as much as possible in evaluating residual risk. Since facility emissions could increase over time for a variety of reasons, and with them the associated impacts, the use of potential or allowable emissions is more appropriate. We believe an analysis based on actual emissions from a single point in time could underestimate the residual risk from a source category.

… In assessing the cancer risks related to the source category, EPA used long-term concentrations affecting the most highly exposed census block for each facility. This analysis dilutes the effect of sources’ emissions by estimating the impact at the centroid of the census block instead of at the property line or wherever the maximum exposed individual is.”

NACAA is calling on the government to re-examine the data in order to protect workers who may be handling this potentially carcinogenic substance on a daily basis. Richard Belzer, in his report on the problems with NTP’s Report on Carcinogens (RoC), also highlighted fiberglass as an example of the inaccuracies contained in the report. The agency’s listings are “not scientific determinations so much as policy decisions justified, where possible, by science,” he explains, continuing:v

“A recent example of delisting is glass wool (i.e., fiberglass), which the NTP listed as reasonably expected to be a human carcinogen in the seventh edition of the RoC (1994), apparently in response to a previous decision by the International Agency for Research on Cancer (IARC) to list it as Group 2B (possibly carcinogenic to humans). After an extended industry research effort, IARC revised its classification downward to Group 3 (inadequate evidence in humans; limited evidence in experimental animals).

… In 2004, industry nominated glass wool for delisting from the RoC, and in 2011 NTP modified its substance profile in the 12th RoC to exclude varieties of glass wool that are not biopersistent in the lung … The path—from not being labeled, to being labeled as a possible human carcinogen, then reasonably anticipated to be a human carcinogen, to once again not being labeled—extended over 20 years. Moreover, the NTP did not delist the substance so much as change its definition to exclude fiberglass.”

Is Fiberglass Safe to Use in Your Home?

This information is one of the reasons that I recently had all the blown in fiberglass insulation in my home’s attic removed and replaced with five inches of blown in foam to completely seal and insulate my attic. Not only did this remove the dangerous fiberglass, which invariably migrates down into the living space but it also closes off the attic space and makes the attic only about four degrees different than the temperature of the living space. Additionally it provides a fair measure of protection from winds as high as 140 mph.

Please understand that fiberglass is a serious issue and if you can it would be wise to consider replacing it in your attic as it’s likely that fiberglass, like so many other man-made synthetic materials, could contribute to health problems if your exposure is significant or recurring. That said, the most significant risk applies to those who live near a production facility or who work with it on a regular basis. Aside from the cancer risks, exposure to fiberglass is known to cause:

  • Irritation to eyes, nose and throat
  • Rash and itchiness
  • Stomach irritation if fibers are swallowed
  • Worsening of asthma and bronchitis

It is not clear at this time whether there is a significant risk to simply living in a home that contains fiberglass insulation, but the research suggests the substance is primarily problematic when stirred up into the air (such as during a remodeling project or upon initial installation).

One caveat, look for the newer formaldehyde-free fiberglass, as the conventional varieties contain this toxin, which can outgas into your home. If you work with fiberglass at all, be sure to wear appropriate protective equipment, including:

  • Long-sleeved work clothes or disposable coveralls
  • A respirator
  • Safety glasses and gloves
  • Open a window or a door to increase ventilation and reduce dust levels
  • Use a shop vacuum after wetting the dust and fibers

Keep in mind, too, that there are many options for insulation other than fiberglass. The following green building products are safe, effective, and will not make your skin irritated and itchy the way conventional fiberglass often does. Plus, some are made from recycled materials or require far less energy to manufacture than fiberglass, making them a positive choice for the environment as well as your health. Options for natural, non-toxic insulation include products made from:

  • Recycled blue jeans
  • Recycled newspapers and paper products
  • Cotton fiber
  • Sheep’s wool


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