The International Agency for Research on Cancer, a part of the World Health Organization (WHO), has removed glass wool fibers from a Group 2B classification ('possibly carcinogenic to humans') to a Group 3 classification ('not classifiable as to carcinogenicity to humans'), according to Camfill Farr.
Manufactured vitreous fibers in the form of wools are widely used in thermal and acoustical insulation and in other manufactured products in Europe and North America. These products, including glass wool, rock (stone) wool, and slag wool, have been in use for decades and have been extensively studied to establish whether fibers that are released during manufacture, use, or removal of these products present a risk of cancer when inhaled.
Through intensive studies conducted since 1988, the IARC has concluded that there is no evidence of increased risks of lung cancer or mesothelioma (cancer of the lining of body cavities) from occupational exposures during the manufacture of these materials, and inadequate evidence overall of any cancer risk.
The IARC had previously classified glass fibers as 2B based upon a study reported in 1972, wherein glass was implanted into the thoracic cavity of a laboratory rat and cancer developed. Unfortunately, the results of this study were questionable, as the amount implanted into the rat equaled one-eighth of the total weight of the rat.
Companies that market competitive media to the fiberglass media used in air filtration products drew parallel assertions, claiming possible health concerns caused by airborne glass fibers shedding from filters into HVAC systems. Legal authorities required one such company to discontinue negative selling techniques, as the claims could not be substantiated by ANY research evidence. Unfortunately, for some end-user customers, the seed was planted; and filter selection in those instances was based upon these negative assertions as opposed to the actual in-place performance values of the filter.
One of the negative parallelisms drawn was that glass fibers were similar to asbestos fibers. An asbestos fiber has a high biopersistence, in that once it is in the respiratory system, its natural characteristics do not allow breakdown by the body's natural protection mechanisms. Although rare, these fibers can develop into cancer over a period of time. Multiple studies have shown that airborne glass fibers do not have a high level of biopersistence, thus eliminating the characteristic most consistent with potential human health problems. Glass fibers have been found to be non-carcinogenic. Additionally, continuous glass filaments, which are used principally to reinforce plastics, are also considered not classifiable as to carcinogenicity to humans.
In any case, the lesson learned from the last 20 years of the glass-synthetic fiber debate should be to make our own judgments based upon a full review of the available materials as published by reputable organizations. In today's air filtration market, we obtain the most consistent particle size versus efficiency with finely extruded fibers. The most common element that may be extruded to this level is glass. The most efficient filters used in today's ultra-cleanrooms are made of microfine glass fibers. Without these glass fibers, we would not have computers, many of today's life-saving drugs and even some common dairy products.