Manufacturers began using fibreglass in the 1920's. The material used to create it--rock, slag and sand combinations--is plentiful and cheap. Use of fibreglass expanded when suspicions began to surface about the safety of asbestos. Fibreglass' similarity in shape and size to asbestos made it equally useful for insulation, and for adding strength and fire safety to products. The same similarity made researchers wonder about the safety of fibreglass.
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One value of fibreglass is the ability to create many different size and shape fibres that then have different properties and uses. E-glass fibreglass serves electrical uses. Its continuous fibres make it perfect for increasing the strength of other materials. Glass wool fibreglass strands are extremely fine and form a wool-like mass. It works well for insulation and to add fire resistance and sound proofing. Manufacturers can also create "special purpose" fibres using combinations of fibres with specific properties such as higher heat resistance or strength.
Larger Fiber Glass Fibers
Fibres with diameters greater than three micrometers and longer than 10 micrometers--one micrometer being one millionth of a meter-- are considered safe according to the American Conference of Governmental Industrial Hygienists (ACGIH) in a report dated 2004. The Environmental Protection Agency says fibres must be smaller than five micrometers to be inhaled. The ACGIH fact sheet says workers in fibreglass factories did not have increased rates of lung cancer.
The ACGIH does consider fibreglass wool as a carcinogen in animals, but the report says that the animal studies did not apply to humans. The researchers' method of exposing the animals--injecting fibres into airways rather than the animals breathing naturally--meant that humans would not likely receive the same kind of exposure that caused cancer in lab experiments.
A report in 2010 by the National Toxicology Program notes that inhaling fibres did increase lung cancers in laboratory animals, and fibreglass wool has diameters as tiny as .05 micrometers, so can be inhaled. Longer, thinner fibres, and "biopersistence"--the ability to stay in the lung tissues--were strong indicators of a fibre potential to make tumours grow, along with the degree of exposure. The "longer" fibres were more than 20 micrometers.
Fibre Types of Most Concern
According to the National Toxicology Program report, the fibreglass most associated with possible cancer is glass wool fibres made into special purpose fibreglass. Two of the many types mentioned are "type 475" and Man-Made Vitreous Fiber (MMVF) 33, which combines type 475 with other types and sizes of glass fibre. Additionally, when lab animals inhaled E-glass fibres, researches found significant increases in tumours, both malignant and non-malignant.
Possible DNA Changes
The report from the National Toxicology Program cited a study done in 2008 (Nguea et al.) that discovered glass wool fibres damaged DNA in cells from mammals, and caused chromosomal abnormalities.
Still Great Disagreement
Reports and opinions by government agencies still have not found proof of cancer in humans related to fibreglass wool, the type used for insulation. All agencies agree that fibreglass is an irritant that can cause temporary skin and eye irritation and difficulty breathing for people exposed. Caution is warranted, but the report from the National Toxicology Program did find reassuringly that fibreglass insulation does not cause appreciable increases in fibreglass exposure in homes.
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