GLASSWOOLFIBRES

Fibreglass is an immensely versatile material which combines its lightweight with an inherent strength to provide a weather-resistant finish, with a variety of surface textures. Glass wool fibres are a sub-category of synthetic vitreous fibres and of inorganic fibrous materials. Glass wools fibres contain aluminium or calcium silicates and a variety of materials, including rock, clay, slag, or glass. The chemical composition of glass wool products varies depending on the manufacturing requirement and end use, but almost all contain silicon dioxide as the single largest oxide ingredient for the production of glass. Commercial glasses also include additional oxides of aluminium, titanium, zinc, magnesium, lithium, barium, calcium, sodium, and potassium. Cytotoxic potencies of the glass wool fibres have been shown to be closely associated with their transforming potencies. Glass wool fibres caused tumours in two rodent species, at several different tissue sites and by several different routes of exposure. Individual types of glass wool fibres were studied in chronic carcinogenicity bioassays in rats and/or hamsters exposed by a number of routes. Inhalation exposure studies showed that tumour incidence or lesion severity increased with the concentration of fibres in the lung. The cumulative lung burden of fibres is related to their deposition and their bio-persistence, which is the ability of fibres to remain in the lung. Also the fibre aerodynamic diameter determines whether a fibre will be deposited in the lungs or the upper airways, and the thinner the fibres, the deeper is their deposition in the lungs. It is important to consider both inhalable and respirable fibres because most human lung cancer occurs within the first five generations of the trachea-bronchial tree.

Glass fibres can generally be classified into two categories based on usage: (i) low-cost, general-purpose fibres typically used for insulation applications and (ii) premium specialpurpose fibres used in limited specialised applications. The primary use of glass wool is for thermal and sound insulation. The largest use of glass wool is for home and building insulation in the form of loose wool; Batts insulation in the form of a blanket, rather than a loose filling; blankets or rolls; or rigid boards for acoustic insulation. Glass wool is also used for industrial, equipment, and appliance insulation. Special-purpose glass fibres are used for a variety of applications that require either a specialised glass formulation or a particular diameter. The largest market for special-purpose glass fibres is for battery separator media; the glass wool fibres physically separate the negative and positive plates in a battery while allowing the acid electrolyte to pass through. Another important use is in high-efficiency particulate air filters for settings where high-purity air is required. Special-purpose glass fibres are also used for aircraft, spacecraft, and acoustical insulation.

Glass wool fibres have the potential to cause genetic damage. In vitro studies in cultured mammalian cells showed that glass wool fibres caused DNA damage, micronucleus formation, chromosomal aberrations, and DNA–DNA inter-strand cross links, and longer fibres have been reported as more potent in inducing these geno-toxic effects. Fibres of various dimensions caused DNA damage in mammalian cells. Also, intra-tracheal instillation of insulation glass wool caused DNA strand breaks in rat alveolar macrophages and lung epithelial cells. Cytotoxicity studies indicated that longer fibres of glass wool caused more toxic effects than shorter fibres to rat alveolar macrophages. Exposure to glass wool fibres also caused cytotoxicity and morphological transformation in Syrian hamster embryo cell cultures. The safety regulation limits for glass wool fibres set by the American Conference of Governmental Industrial Hygienists (ACGIH) and the National Institute for Occupational Safety and Health (NIOSH) are as follows:
1. The ACGIH: Threshold limit value (TLV) and time-weighted average (TWA) limit: 1 fibre/cm3 for respirable fibres.
2. The NIOSH recommended exposure limit (REL) for the fibrous glass dust is
3 fibres/cm3 (TWA) (refer to literature for details).