Schools and other buildings occupied by children need special consideration since children may have a higher lifetime risk than adults of developing asbestos-related disease.

There are a number of key aspects to be considered:

• A systematic approach to decision-making is needed in relation to management or remedial measures for asbestos-containing materials in buildings.
• Consideration must be given to the different types of asbestos-containing building products in terms of their composition, potential for release of fibres during normal use, and fibre type.
• There is a need to take account of priorities, especially if amphibole asbestos is known to be present.
• There must be sensible handling and proper control during remedial processes, which must be followed by an adequate inspection. Legislation is needed to ensure that work has been carried out properly.
• The costs of carrying out certain remedial measures may be high.
• Reentrainment of asbestos-containing dust to the air must be limited.
• The handling and disposal of asbestos-containing waste from buildings and during demolition needs great care. Loose, friable, asbestos-containing material should normally be removed from buildings prior to demolition.

It is important to distinguish initially between the different types of asbestos-containing construction products which are, or have been, used in public buildings, since the potential for fibre release from these materials and the need for corrective action varies. Firstly, there are low density, friable or crumbly asbestos-containing materials, such as asbestos-containing sprayed insulation and asbestos-containing pipe and boiler insulation. These materials were used extensively between the 1940s and the 1970s in buildings, principally in North America and Europe. Fibres are most likely to be released when this material is disturbed or when maintenance or renovation work is performed.

The second category of asbestos-containing products used in buildings is hard, high density material, in which the asbestos fibres are firmly embedded in a matrix and unlikely to be released during normal use. Examples include floor tiles, asbestos-cement products, and hard ceiling tiles. Fibres are mainly released from these products during sanding, grinding, cutting or other work during their installation, renovation, removal or demolition.

It is important to follow a logical systematic approach in assessing the type of control action that is required to reduce exposure to asbestos in public buildings. A decision tree model would seem to be particularly appropriate. One such model for friable asbestos-containing materials is presented in Figure 1. Management or remedial action for other types of asbestos-containing materials (i.e. hard materials such as asbestos-cement products) is not normally necessary since these materials rarely present undue risks to the health of the building occupants.

Preventive management programmes for asbestos-containing materials which are not releasing dust can include good record-keeping of their location, labelling of those materials which may be disturbed, public education, periodic re-inspection, and minor repairs. Based on considerations of cost, the possibility that removal may pose a risk to public health if it is not carried out properly, and that workers may be exposed to elevated airborne levels of asbestos during the operation, removal of asbestos-containing materials should be considered only as a last resort unless it can be firmly established that the health risk is unacceptable or cannot be reduced sufficiently by other means. Factors which should be carefully considered before undertaking any removal of friable asbestos-containing materials include:

€ the risk resulting from the removal;

€ the type of occupancy and the most common activities in the building;

€ the accessibility of the material;

€ the protection of other parts of the building against contamination;

€ the replacement of the material;

€ the fire protection requirements of the building;

€ the cost/benefit evaluation of the removal;

€ the availability of properly trained personnel for the remedial action;

€ the need to monitor before, during and after the remedial measures.

If removal of asbestos-containing materials from buildings is undertaken, the method employed should be designed to produce the minimum release of asbestos fibres in the air. The method should not result in increased airborne concentrations inside the building after the action is complete. To minimize potential problems, the control of airborne emissions during removal may be achieved by appropriate technology, including prior wetting of the material with water and surfactant (or equivalent). Dry removal may be the only option in some instances, direct removal by vacuum methods with high efficiency filters (HEPA) being recommended. Wet-wiping of surfaces, followed by HEPA vacuuming after a suitable drying period, is the most suitable method for cleaning non-porous contaminated surfaces.

In the case of building demolition, a decision-tree model is again applicable. In addition, precautions should be taken to avoid undue exposure to anybody living or working in the vicinity during and after the demolition process.

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4. ASBESTOS IN THE PRODUCTION, MAINTENANCE AND USE OF
       VEHICLES

The Working Group discussed two main aspects of this subject:

• risks of asbestos-related disease in garage workers and mechanics resulting from inhalation of fibres from friction materials (brake linings and clutch plates);
• risks to the general public in urban areas resulting from fibre release during the braking of vehicles.

4.1   Occupational risks
In the two available cohort studies of workers in the manufacture of friction products, one of which was conducted in the United Kingdom and the other in the USA, the risks of lung cancer and mesothelioma were very small. Mesothelioma were observed in workers only in a small section of the British factory using crocidolite. Although there have been a few case reports of mesothelioma among garage mechanics (a very large occupational group), there was no excess risk in this group in a systematic case-control survey of mesothelioma in the USA and Canada.

The Working Group concluded, therefore, that provided good work practices were followed and that neither amphibole fibres nor substitute materials with similar potential to cause disease were used in friction products, detectable risks in vehicle maintenance and repair workers are not expected.

However, some agencies have estimated excess deaths associated with exposure to asbestos in this occupational group on the basis principally of exposure-response relationships for lung cancer in several different industries. Since the slope of the exposure-response relationship for lung cancer in friction material production workers is much less than in other production industries, the excess deaths in brake manufacture and repair workers may have been overestimated by this approach.

Appropriate work practices for the maintenance and repair of asbestos-containing friction materials in vehicles include a dry method employing a high efficiency filter vacuum with an enclosure. A less efficient system, but one which can be employed if the vacuum and enclosure are not available, involves the use of liquid cleaning solution applied by spray or brush, together with a drip pan to collect the waste-water. A minimal version of this is a simple wet sponge or brush used to apply a soap solution.

The Working Group recommended that the use of compressed air to clean out brake drums be prohibited, unless it is associated with an enclosure maintained under negative pressure. Also to be avoided is the drilling or grinding of brake linings (often undertaken to correct noisy and/or uneven braking) without proper precautions. These include the use of vacuum hoods, exhaust ventilation and, where necessary, positive pressure or approved filter respirators.

4.2   Pollution of the general environment
The possible emission into the general environment of asbestos fibres during the use of vehicle brakes was reviewed. The very high temperatures generated at the drum-lining interface generally result in destruction of the fibrous nature of chrysotile. Nevertheless, some intact, though usually short fibres, could be released. In areas of heavy traffic or in poorly ventilated tunnels, this could make some measurable contribution to the asbestos fibre content of urban air. On the basis of available data, the extent of this contribution could not be assessed; however, it is probably very small.

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5. TRANSPORTATION, STORAGE AND DISPOSAL OF ASBESTOS

The Working Group considered that it was generally appropriate to:

€ remove asbestos-containing material separately with minimum disturbance, where possible;

€ keep surfaces and material damp (using low-foam detergents);

€ avoid creating dust;

€ transport in covered vehicles or bags;

€ bury as soon as possible at a waste-disposal site.

An example of a decision-tree model for disposal of asbestos-containing waste is shown in Figure 2. More detailed information is included in the background paper entitled "Collection, Transportation, Storage and Disposal of Asbestos-Containing Waste".

In some situations and countries, the following aspects may require special attention:

• there is a need to define "asbestos-containing waste" (i.e., percentage content);
• huge volumes of waste may be generated by mining and milling of asbestos;
• burial under a cover of earth (i.e., landfill disposal) is usually the most appropriate disposal method for asbestos-containing waste, though the appropriate depth of coverage and type of material will vary;
• possible contamination of water supplies, including those underground in the vicinity of asbestos-containing waste-disposal sites may occur.

To avoid potential future problems, it is important to maintain good records of asbestos-containing waste-disposal sites.

More specifically, the following aspects need to be considered:

• the selection of appropriate detergents and concentrations to use in water applied to asbestos-containing waste; e.g., some domestic detergents are appropriate; these should be added to water to provide a solution which has a lowered surface tension (e.g., below 35 dynes/cm);
• the selection of chemical stabilizing agents that form a crust or layer resistant to air and water erosion (e.g., reagents that have a bituminous, resinous adhesive or elastomeric polymer base; one such stabilizer is calcium lignosulfonate);
• the selection of the types of container for transportation and deposition (e.g., plastic of various gauges, metal, etc.), depending on the nature of the asbestos-containing waste.

In industry, asbestos-containing waste is frequently recycled. However, the recycling of asbestos-containing waste from buildings is not considered desirable, particularly for friable materials and those containing amphibole asbestos.

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6.     CONCLUSIONS AND RECOMMENDATIONS

6.1   Conclusions
The reduction of environmental pollution by respirable asbestos fibres is a desirable public health objective, though the degree of priority afforded to this objective may vary in different countries and under various conditions. Factors which require consideration in establishing this priority include socio-economic circumstances, health and hygiene needs of the population, the availability of engineering skills and equipment, the age-groups at risk and the contribution of smoking to the risk.

As the purpose of population control is the promotion of public health and the prevention of disease - in this case, particularly mesothelioma and lung cancer - the rationale for any control programme is highly dependent on the state of knowledge and interpretation of available data on health risks. The Working Group accepted the importance in this respect of Environmental Health Criteria No. 53: Asbestos and Other Natural and Mineral Fibres, but recognized that there were differences of opinion on certain relevant aspects of exposure-response relationships for asbestos-related diseases. These aspects include the validity of linear non-threshold models and the importance of fibre dimensions, fibre type, and industrial process. To minimize non-productive discussion of these differences, the Working Group concentrated on the definition of some general guidelines and priorities for control that would be appropriate for most interpretations of the health-related data.

The problems which the working group were asked to review were difficult to define, enormously varied and highly technical. It was beyond the scope of a short meeting by a small number of participants, without access to all relevant knowledge, and experience, to draw more than tentative conclusions. The great importance of the problems under review was unanimously accepted and it was strongly recommended that they should be the subject of further comprehensive study and discussion. Even at this stage, however, certain basic principles could be defined. Actions taken to reduce asbestos fibre pollution should be based on full and objective consideration of costs and benefits. A systematic decision-making process has therefore to be followed for each situation and steps need to be taken to ensure that control measures are in fact beneficial. When hazards cannot be adequately controlled, the need to ensure that substitute materials do not present similar risks was recognized.

6.2     General recommendations

1. Countries that do not have established policies for the control of hazards related to the presence of asbestos in the environment should develop guidelines for this purpose. These should include provisions for cleaning areas where damaged friable asbestos-containing material is present in considerable amounts in public buildings or as a result of uncontrolled disposal practices. Such plans might usefully include management guidance such as decision-tree charts adapted to existing national or local circumstances, requirements, and economic possibilities. Examples of such charts are presented in Figures 1 and 2.
2. In all situations where asbestos is being handled or manipulated, the guidelines set out in the International Labour Organization handbook "The Safe Use of Asbestos", should be closely observed. Safety in the use of Asbestos - an ILO Code of Practice (International Labour Organization, Geneva, 1984, 129 pp.)
3. The use of sprayed-on and low density insulation materials containing asbestos should be strongly discouraged on a worldwide basis.
4. In any given situation, priority should be given to the control of air pollution by amphibole asbestos fibres (crocidolite, tremolite, and amosite). This is not to underestimate the potential adverse health effects of chrysotile fibres.
5. Priority should be given to the control of potentially hazardous exposures to young children.
6. The legitimate needs of developing countries for materials for construction, water supplies and sewage control should be recognized. Where asbestos-containing products are used to meet these needs, every assistance should be offered to ensure their safe use.

6.3   Specific recommendations

6.3.1   Asbestos in public buildings

1. The presence of friable asbestos-containing materials having the potential for fibre release should be identified by inspections and, so far as possible, proper maintenance ensured. In all such buildings, special attention should be given to approved cleaning methods to prevent dust accumulation becoming a source of airborne asbestos.
2. In situations where fibre release presents a significant risk, repair, encapsulation, or enclosure should be undertaken wherever practicable. Removal should only be considered if there is no satisfactory alternative.
3. If removal in undertaken, it should be by trained or licensed workers using procedures to ensure their own safety and that of the general public and future occupants. This may require environmental measurement before, during and after the work is undertaken.
4. When a building is to be demolished, friable asbestos-containing materials should first be removed with priority given to thermal and sprayed insulation.
5. High-density asbestos products, such as asbestos-cement and asbestos fire-board, in normal condition and use should not create an unacceptable hazard, but care is needed to contain airborne dust during installation and maintenance of these products.

6.3.2   Asbestos Waste Disposal

1. Friable asbestos-containing waste should be carefully bagged and disposed of, preferably in landfill sites according to well-defined national regulations.
2. Prior to transportation, friable asbestos-containing waste should be adequately wetted. It should be transported in leak-tight containers in covered vehicles to a disposal site and disposed of in accordance with well-defined national regulations.
3. Disposal sites should be subject to specific provisions to avoid environmental contamination at any stage during use or after closure.
4. Demolition debris contaminated with asbestos should be minimized to the extent possible, kept wet, and transported rapidly in bulk to a disposal site.
5. Asbestos waste should be adequately covered prior to compaction and further covered within the same day that the asbestos waste is deposited at the site. When a disposal site is closed or inactive for a period of over a year, a final cover should be applied sufficient to prevent uncovering of the waste by wind and water erosion.
6. A surfactant solution (wetting agent) should be used when wetting waste from friable asbestos containing materials prior to removal.

6.3.3   Friction Materials

1. Poor work practices in the installation and repair of asbestos-containing friction materials can give rise to potentially hazardous levels of exposure. Safe work practices should be promoted and uncontrolled compressed air blowing of brake and clutch debris strongly discouraged.
2. The use of asbestos-containing friction materials does not pose a detectable risk to the general population. Potential emissions from braking cannot be quantified form available data. Only in tunnels and other very enclosed areas is it likely that adequate ventilation to prevent build-up might be indicated.

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