In North America, the policy debate over management versus immediate universal removal of in-place friable asbestos insulation materials, was effectively concluded in September 1990, following the publication of the U.S. EPA Green Book, entitled "Managing Asbestos In Place". Consistent with many scientific reviews on the subject, it is now generally agreed that intact, undisturbed asbestos-containing materials, generally do not pose a health hazard. Therefore, unless ACMs are in poor condition or located where they can be easily disturbed, the best approach is to manage the problem and defer removal until the time of major renovation or demolition of a building.
This conclusion is based on EPA's 5 facts:
1. Although asbestos is a hazard, the risk of asbestos-related disease depends upon exposure to airborne asbestos fibres.
2. Based upon available data, the average airborne asbestos levels in buildings seem to be very low. Accordingly, the health risk to most building occupants also appears to be very low.
3. Removal is often not a building owner's best course of action to reduce asbestos exposure. In fact, improper removal can create a dangerous situation where none previously existed.
4. EPA only requires asbestos removal in order to prevent significant public exposure to airborne asbestos fibres during building demolition or renovation activities.
5. EPA does recommend a proactive, in-place management program whenever asbestos-containing material is discovered.
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The health hazards related to the exposure to fibrous materials other than asbestos are attracting increasing attention from both the international scientific community and health agencies. Mounting scientific evidence as well as recent international regulatory developments underscore the soundness of these concerns.
In the U.S., fibreglass has recently been listed by the Department of Health and Human Services as a substance "reasonably anticipated to be a carcinogen". Refractory ceramic fibre (RCF) has also been listed as a "probable human carcinogen", and concerns have been raised regarding the health effects of silicon carbide whiskers used as in composite materials. In Germany, the MAK Commission, the agency responsible for producing an annual list of hazardous substances, has classified ceramic fibre as "a substance with known carcinogenic potential in humans." and listed other man-made mineral fibres, such as glass fibre and mineral wool, under a new category, "to be treated as if a probable cause of cancer". Slag wool is defined as "possibly carcinogenic".
Canadian authorities have reached similar conclusions for refractory ceramic fibre, which has been classified as "probably carcinogenic to humans", and rock/slag wool which have been identified as
"possibly carcinogenic to humans". However their position regarding fibreglass differs - Health Canada considers it unlikely that fibreglass is carcinogenic to humans.
Another report on selected synthetic organic fibres published in 1993 by the International Programme on Chemical Safety, a World Health Organization affiliate, concluded that all organic fibres that are respirable and durable are of potential health concern. The report recommended that, "exposures to these fibres should be controlled to the same degree as that required for asbestos until data supporting a lesser degree of control become available -- and that the available data suggest that para-aramid fibres fall within this category."
€ ILO Group of Experts meeting
In April 1989, the International Labour Organization convened a Group of Experts meeting on Safety in the Use of Mineral and Synthetic Fibres. The meeting concluded that long, thin, durable fibres appear to be most hazardous to health and that in all cases the objective should be the
reduction of human exposure to airborne respirable fibres.
The meetings also provided general advice on appropriate preventive and control measures for work with man-made mineral and synthetic fibres, including exposure limit values for total dust and respirable fibre concentrations, labelling, work practices, including engineering controls, housekeeping and personal protective equipment, monitoring of the workplace environment, health surveillance of workers and instruction, training and information for workers. It was also recommended that a Code of Practice on Insulation Wools be developed on a priority basis.
€ All fibres are not equally hazardous
As in the case of the asbestos family of fibres, it appears that not all man-made fibres are equally hazardous. Again the 3 D's - Dose, Dimension and Durability, must be applied in determining the health risks of various fibrous substances.
To illustrate, a recent conference was held by WHO/IARC on "Biopersistence of Respirable Synthetic Fibres and Minerals". Data presented at the Symposium showed that various types of glass fibres also have different solubilities and biopersistence characteristics, which may vary according to their respective manufacturing process and chemical composition. Thus, glass fibres with high Aluminum (Al) content were shown to be more durable than those with low Al content. The same observation has been made with respect to refractory ceramic fibres (RCF), where it was found that a high Al203 content has a negative influence on biosolubility, whereas high concentrations of alkaline oxides have the opposite effect. A major study by German scientists of the Fraunhofer Institute in Hannover compared a whole series of MMMFs (from glass to RCFs) and natural fibres for in vivo durability. Half-times for fibre elimination from the lung ranged from 10 to 500 days. Another study from the USA also reported that inhaled RCFs showed no chemical alterations 2 years following end of exposure, whereas glass fibres showed that some components had leached. Another study from the Institute of Occupational Medicine in Edinburgh showed that, in experiments using rats, chrysotile asbestos and glass fibres were cleared at approximately the same rate, whereas there was very little clearance of crocidolite asbestos.
The general conclusion from this International Symposium, which was held in September 1992, is that RCFs are certainly not cleared rapidly from the lung; some MMMFs are cleared much more slowly than others; and, the same is true for asbestos fibre types, where it is recognized that amphiboles, in particular crocidolite and amosite have clearance half-times in the range of decades,whereas chrysotile is cleared within weeks or a few months.
Based on the durability factor alone, the most recent data available point to the existence of a continuum of pathological potential for all respirable fibres, natural and man-made, from very low potential (highly soluble, short biopersistence) to very high potential (low solubility, long biopersistence) (see Figure I).
The Scientific implications of such a continuum of pathogenic potential for exposure standard setting are obvious: a continuum in exposure standards, from the relatively less stringent through increasingly more stringent levels, up to prohibition.
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At high and prolonged levels of exposure, chrysotile asbestos can present potential risks to worker health. However, there is broad scientific consensus that provided they are properly controlled and used, chrysotile asbestos and its modern day products do not pose risks of any significance to public or worker health and the general environment. This view is shared by international health organizations and most countries around the world.
However, while the philosophy of controlled-use is one thing, practical reality is quite another. To reinforce confidence in controlled-use as an appropriate regulatory approach, the international asbestos industry must demonstrate in a very clear and visible fashion that chrysotile asbestos and its modern day products are being properly handled and used, not only in factories, but on a product life-cycle basis. Without such demonstrations, science holds little importance.
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