Question Dealing with Special Purpose Fibers

[krouton]

I worked for a year in a fiberglass shop. They used a needled mat material, it was Continuous glass filament chopped E-Glass made of mostly silcon, calcium, and aluminum. They say it had a diameter of 6 micrometres and it was non-respirable, and couldn't reach the deep lung. Most of the glass was contained in sheets and covered. But a lot of times when cooking the material the ventilation for the oven was not properly installed, and the fibers went into the air. For about a month or two, I also trimmed plastic parts containing amounts the same material creating a lot of dust. What scares me, is E-glass is shown to cause cancer in respirable form. When they say the products I worked with were non-respirable, with small traces of respirable fibers which are cancerous, should this cause worry after working with it for a year? I found a study that compared respirable E-glass to amosite asbestos, with almost the same results. This is what worries me. Are non-respirable fibers, really non-respirable?

Thanks,
Joe

[National Jewish Health]

The product you are referring to sounds like a typical continuous filament glass fiber.  Fiberglass or continuous filament glass fiber products are part of a class of fibers referred to as synthetic vitreous fibers (SVF).  The ability of these fibers to cause serious chronic lung disease, including fibrosis and lung cancer, is related to both the size, measured as the diameter or width of the fiber, and the durability of the fiber.

The size of the fiber determines whether it can successfully travel through the upper respiratory system to reach the deeper regions of the lung where oxygen is absorbed and fibrosis or lung cancer can develop.  Research has shown that the vast majority of fibers greater than 3 microns in diameter become trapped in the upper respiratory system where they are efficiently removed by the normal upward movement of mucus.  Fibers greater than 3 microns in diameter have not been associated with chronic lung disease.  These larger fibers can cause skin and upper respiratory irritation, but these effects are reversible on removal from exposure and appear unlikely to lead to serious health consequences.

The durability of a fiber determines how long it will remain in the lung once it is deposited there.  In general, research suggests that the longer a fiber remains in contact with lung tissue, the more likely it is to cause fibrosis and possibly lung cancer.  Most continuous filament glass fibers are removed from the lung through chemical and cellular processes at least 5 times faster than the more potent forms of asbestos (crocidolite and amosite).  Currently, the prevailing opinion in the medical community is that due to the lower durability of continuous filament glass fibers, the risk of lung cancer or fibrosis due to exposure is much lower than asbestos or ceramic fibers.

You report the fiber size for the product you were using was 6 microns.  Usually this size refers to the nominal or average fiber size.  This does not mean that all fibers in this product are 6 microns.  While the product likely contains a fraction of fibers in the respirable size range less than 3 microns, it is not likely the fraction is significant.  The manufacturing process for continuous filament glass fibers usually controls the size range of the fibers very well with reports of fibers not varying by more than 10% of the nominal fiber size.  In addition, while asbestos fibers tend to split longitudinally into smaller diameter fibers when cut or abraded, fiberglass only breaks up into shorter pieces of the same diameter.  Since the diameter of the fiber determines where in the lung the fiber will deposit, this is a very important difference.

To summarize:  
1) The risk of lung cancer from exposure to respirable fiberglass appears to be much lower than for asbestos exposure.
2) Exposure to non-respirable fiberglass has not been associated with lung cancer.
3) When working with a continuous glass filament product with a nominal fiber size of 6 microns as you describe, it is unlikely that exposures to respirable fibers exceeded recommended levels.  However, please realize that this assessment is based on your limited description of the product and processes and actual exposures may be higher.