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close this bookBuilding Materials and Health (UNCHS/HABITAT; 1997; 74 pages)
View the documentABBREVIATIONS
View the documentFOREWORD
View the documentINTRODUCTION
View the documentA. Introduction
View the documentB. Health and building materials: An overview
View the documentC. Asbestos
View the documentD. Metals
View the documentE. Solvents
View the documentF. Formaldehyde
View the documentG. Insecticides and fungicides
View the documentH. Timber
View the documentI. Silica dust
View the documentJ. Earthen and traditional materials
View the documentK. Radon and its sources
View the documentL. Wastes
View the documentANNEX
View the documentREFERENCES

C. Asbestos

Sources and health implications

The term asbestos covers a number of naturally-occurring fibrous silicate materials in rock formations widely distributed in the earth’s crust. However, only a few of the deposits are commercially exploitable. The principal varieties of asbestos used commercially are chrysotile (hydrous magnesium silicate), a serpentine mineral, and crocidolite (iron and sodium silicate) and amosite (iron and magnesium silicate), both of which are amphiboles. Anthophyllite, tremolite, and actinolite asbestos are also amphiboles, but they are rare, and the commercial exploitation of Anthophyllite asbestos has been discontinued (6).

While the properties of asbestos have been known for thousands of years, it is only in the last century, that the manufacture of building materials incorporating asbestos has been carried out on an industrial scale (7). The main use of asbestos fibres is in the manufacture of asbestos cement products. The products are based on the addition of asbestos fibres (around 10-15 per cent by weight) to a non-combustible filler such as Portland cement. Asbestos cement is a high-compression, high-density, hard-surfaced material which is commonly employed for fire protection panels, corrugated panels for roofing and cladding, roof tiles, fire surrounds, rain water goods, water tanks and water pipework etc. (8). The second largest use of asbestos fibres in the United States of America is the asphalt and vinyl floor tile manufacturing industry. Increased use of these types of tiles in many countries is due to their durability and impermeability to water (9).

Table 2. Principal varieties of asbestos, their theoretical formulae, world output (1984) and common uses in building materials.


Theoretical formula

Output tonnes

Building materials

Chrysotile (White asbestos)


4,058,000 (96.6 per cent)

Lightweight insulation and lagging, filler in plastics and roofing felts

Crocidolite (Blue asbestos)


89,000 (2.1 per cent)

Sprayed steel coatings, pipe seals, additive to cement and board products

Amosite (Brown asbestos)


30,000 (0.79 per cent)

Insulation board, ceiling tiles, asbestos cements and laggings



20,000 (0.48 per cent)





High temperature applications




With other types


Source: Spence, R. J. S., Cambridge Architectural Research Limited (UK), Building Materials and Health (Unpublished draft report prepared for the United Nations Centre for Human Settlements (Habitat), September 1994).

Note: The world production of asbestos has significantly changed since 1984. It was 4.3 million metric tons in 1988, 4.0 million tons in 1990, 3.5 million tons in 1991, and 3.1 million tons in 1992 (United States Department of Interior, 1993: Asbestos in 1992. Mineral Industry Surveys; United States Bureau of Mines, 1993). Out of the 3.1 million tons in 1992 more than 95 per cent was chrysotile. Amphibole production has declined sharply, with South African production of crocidolite and amosite dropping from 280000 tons in the late 1970s to 55000 tons in 1992 (Industrial Minerals, 1992: Asbestos Production: The Chrysotile Crysis?). The last amosite mine, which operated in South Africa, closed in 1992. The total United States consumption of asbestos in 1991 was 34000 metric tons, and in 1992 only 33000 metric tons. Only 500 metric tons of crocidolite was consumed in 1992 and no amosite (United States Federal Register, vol.59, No. 153. Occupational Exposure to Asbestos; Final Rule, p.41027).

Epidemiological studies, mainly on occupational (mining and milling, manufacturing, or product application) groups, have established that all types of asbestos fibres may be associated with asbestosis, bronchial carcinoma, and mesothelioma (9). A brief account of these health problems is as follows (7, 10, 11):


• Asbestosis. This is a deposition of fibrous tissues in the lung parenchyma - the region where oxygen exchange takes place. Initial coughing is followed by progressive difficulty in breathing. The patient may eventually die of cardio-respiratory failure. Severity of the disease is related to cumulative exposure to asbestos (a dose relationship), although it may be arrested in the early stages if contact with asbestos ceases. Asbestosis has a long latent period, rarely being seen less than 10 years after first exposure to asbestos. It seems that there is a threshold level below which the condition does not occur;

• Bronchial carcinoma (lung cancer). As with, asbestosis, there is a dose relationship but it is uncertain whether there is a threshold level below which there is no risk. There appears to be a multiplicative effect on smokers: the risk to asbestos workers who smoke is ten times as great as to non-smokers;

• Mesothelioma. A malignant tumour on the lining of the chest cavity (pleural mesothelioma) or abdomen (peritoneal mesothelioma). The latent period for the disease is very long - an average of more than 30 years from first exposure. Mesotheliomas have a very poor prognosis, being unresponsive to most cancer therapies; and

• Non-malignant conditions such as diffuse thickening or effusion (fluid in the lungs). These lung abnormalities may cause breathlessness but are often asymptotic.

Already in 1987, a WHO publication (37), the “Air quality guidelines for Europe”, described, inter alia, the carcinogenic effect of asbestos. In addition, the European Community has issued several directives in which the marketing and use of dangerous substances are regulated, e.g. Council Directive 76/769, and the fifth and seventh amendments to this directive provide for restrictions on the marketing and use of asbestos. Germany has incorporated the provisions of these directives in its national legislation. Except for some negligible exemptions, asbestos is prohibited in Germany.

Health risks due to exposure to different asbestos types are dependent on the fibrous structure of the material, thus asbestos types which are liable to form fibres less than 3 microns in diameter, principally the amphiboles, are most hazardous (10). The fibre length is also important, with fibres longer than approximately 8 microns posing greatest risk. The principal risk is through inhalation of airborne fibres, since there is little chance that fibres will penetrate the skin or be absorbed from the digestive tract.

Past exposure to asbestos in industry or in the general population has not been sufficiently well documented to make an accurate assessment of the risks from future levels of exposure, which are likely to be low (6). There are two possible approaches for assessment of risks, one based on a comparative and qualitative evaluation of the literature (qualitative assessment), the other on an underlying mathematical model to link fibre exposure to the incidence of cancer (quantitative assessment). Attempts to derive the mathematical model have had limited success (6). However, on the basis of qualitative assessment, the following conclusions have been drawn (9):


• Among occupational groups, exposure to asbestos poses a health hazard that may result in asbestosis, lung cancer, and mesothelioma. The incidence of these diseases is related to fibre type, fibre dose, and industrial processing;

• In para-occupational (neighbourhood of an asbestos industrial plant, or home of an asbestos worker) groups, the risk of mesothelioma and lung cancer is generally much lower than for the occupational groups. Risk estimation is not possible because of the lack of exposure data required for dose-response characterization. The risk of asbestosis is very low;

• In the general population, the risks of mesothelioma and lung cancer attributable to asbestos cannot be quantified reliably and are probably undetectable by epidemiological method. The risk of asbestosis is virtually zero;

• On the basis of available data, it is not possible to assess the risks associated with exposure to the majority of other natural mineral fibres in the occupational or general environment. The only exception is erionite, for which a high incidence of mesothelioma in a local population has been associated with exposure. Such exposure to erionite is exceptional, and exposure-related mesothelioma were described in only one country, being probably the consequence of outdoor exposures since birth (51).

The health hazards associated with use of asbestos in the construction industry have come to a sharper focus in recent years: there has been a growing alarm about risks to dangers of breathing fine asbestos. On the other hand, there are others who believe that not enough toxicological and medical data are available to justify a ban on asbestos and asbestos products and that a lot more research is necessary before a judgment could be arrived at, and that the existence of asbestos related diseases reflects neglect of working conditions in the factories and ignorance regarding the science of occupational diseases associated with asbestos in the past (12). However, due to the undisputed fact that asbestos is one of the identified carcinogens, in many countries the manufacture and use of asbestos-based products have been strictly controlled in recent years. For example:


• Use of crocidolite and amosite types of asbestos is increasingly being discontinued (they are banned in the European Union countries and Japan);

• The number of uses and the total consumption of asbestos and its products in the Netherlands have fallen sharply in recent years (13);

• The demand for asbestos was less than one-third in United States of America, in 1987 compared to its peak in 1973 (14). The demand was 672000 metric tons in 1977, and 34000 metric tons in 1991 (Pigg BJ: The uses of chrysotile. Ann Occup Hyg, 1994; 38: 453-458).

• Furthermore, ILO convention 162, requires governments to prohibit the use of crocidolite and spraying of all forms of asbestos (15), and has issued a series of publications namely: The ILO Code of Practice on Safety in the use of Asbestos, 1990; the ILO Occupational Safety and Health Series No. 30 and No. 64; Asbestos: Health Risks and their Prevention, 1974; Safety in the Use of Mineral and Synthetic Fibres, 1990 and the ILO Convention concerning Safety in the Use of Asbestos, 1986 (No. 162) and its accompanying Recommendation, 1986 (No. 172).

Recently the São Paulo Declaration, an outcome of the Asbestos International Seminar: Controlled Use or Ban, held in Sao Paulo Brazil in March 1994, demanded the prohibition of all uses of asbestos and the promotion of substitutes which are less dangerous to the health and safety of workers (16).

The United States EPA in 1989 issued a Rule to prohibit the future manufacture, importation, processing, and distribution of all types of asbestos in almost all products, however the rule was overturned by a United States Court of Appeals in 1991. As a result, most asbestos products are not subject to the Ban and Phase out Rule (Prof. F. Valic, IPCS Consultant and Chen, B. H., WHO).

In spite of the opposing views about asbestos, the controlled use of asbestos appears to be favoured by agencies such as ISO, ILO, the United Nations Economic Commission for Europe, OECD, and the Commission of European Union (EU) (12). However, substitution of asbestos should be considered when safe control cannot be assured. While waiting for the time when it will be economically feasible to ban asbestos use all around the world, WHO recommends: Workers in asbestos industries must wear protective respiratory equipment and never smoke any tobacco; there is no risk from using water pipes in asbestos-cement; and the risks from asbestos-cement roofs are kept properly lined and maintained in such a way as to prevent fibre emissions.

Factors influencing exposure

Risk groups which may be exposed to high asbestos levels are: workers in asbestos manufacturing and processing industries, and maintenance and demolition workers (13). Risks to construction and maintenance workers and building occupants occur when the material containing asbestos is subjected to rough mechanical treatment releasing respirable fibres into the air. Installed components, for example sheet materials which may be sealed by a layer of paint, pose little risk unless degradation occurs by physical abrasion. Chemical attack is a possibility in the case of asbestos cement products in contact with water (especially if “aggressive” due to pH rating and ion content), for example roof sheets and downpipes (17).

The most serious risks to construction workers are likely to be associated with demolition, or programmes of removal aimed at eliminating asbestos products from a building. There are often problems in identifying components which contain asbestos, particularly since many are virtually indistinguishable from the substitute materials which have been developed incorporating man-made mineral fibres. Sampling and analysis by experts in the field may be necessary for correct identification.

Since stripping of asbestos-containing materials often raises exposure levels for building occupants as well as the contractors for a considerable period of time, the risks involved in such actions must be carefully balanced against predicted risks if the materials remain in place. In-situ repair work and sealing may be preferable to full-scale removal, particularly if the asbestos is in a relatively inaccessible location. Heavy physical exertion increases the respiration rate and thereby the exposure dose. Smokers too constitute a risk group with an increased susceptibility to lung cancer.

Acceptable exposure levels

Most developed countries have regulated their asbestos industries, with specified limits to asbestos exposure. In the United Kingdom of Great Britain and Northern Ireland (UK) for example, control limits and action levels are set out by the Control of Asbestos at Work Regulations 1987 (amended 1993). At exposures above the control limit, respirators fitted with the correct filter must be worn. In applying the exposure limit, “fibre” is defined as a particle with length more than 5 microns, diameter less than 3 microns and ratio of length to diameter greater than 3:1. For chrysotile alone, the control limit is 0.5 fibres per millilitre (f/ml) of air averaged over 4 hours, or 1.5 f/ml averaged over any 10 minute period. For any other type of asbestos, whether or not mixed with chrysotile, the corresponding limits are 0.2 and 0.6 f/ml. If workers’ exposure exceeds the action level, the employer is obliged to arrange medical examinations at a maximum of 2 year intervals and to keep accessible medical records for at least 40 years.

In the case of the United States of America, the United States Environmental Protection Agency (EPA), in 1988 took new regulatory action on additional protections to state and local government employees covered by the EPA asbestos abatement worker protection (6). EPA defines “fibre” as a particulate form of asbestos 5 micrometres or longer, with a length-to-diameter ratio of at least 3 to 1. The Permissible Exposure limit to workers exposed to airborne asbestos being 0.2f/cc of air, averaged over an 8-hour day. The action level is 0.1f/cc averaged over 8 hours. The action level is the level at which employers must begin activities such as air monitoring, employee training, and medical surveillance. WHO recommends that, inside buildings the concentration of asbestos fibbers must stay below 500 fibbers per cubic meter. In the case of environmental exposure, it has been estimated that fibre concentrations are unlikely to exceed one thousandth of the control level (18). A typical situation might give a lifetime excess risk of death from mesothelioma of 1 or 2 in 10,000 (18). For lung cancer, the same source predicts an excess mortality of two per million. As noted above, there appears to be a threshold effect for asbestosis which limits its impact to workers in the asbestos industry, with little if any effect on those subject to non-occupational exposure. However, the United States OSHA has recently issued a new Rule on Occupational Exposure to Asbestos (United States OSHA, Department of Labour: Occupational Exposure to Asbestos. Federal Register 1994, Vol. 59, No. 153, 40964-41158) for general industry, construction and shipyard industry specifying permissible exposure limit of 0.1 fibre/cm3 of air as an 8-hour time-weighted average, and an excursion limit of 1.0 fibre/cm3 of air as averaged over a sampling period of 30 minutes. Special attention is given to exposure of workers during repair and maintenance of automotive brakes and clutches, and to exposure of custodian staff.

Mitigation strategies

Construction activities (including renovation, demolition and insulation) should be designed and planned to eliminate or reduce the need for mineral-fibre - based materials which have a cancer producing potential. Stringent handling regulations in the manufacture, use, transportation, demolition, storage and disposal of asbestos must be established. These could potentially be extended to MMMFs if continued monitoring of their effect shows that to be necessary. In view of the reported carcinogenic properties of asbestos after inhalation, exposure via the respiratory route should be avoided as far as possible. To avoid eye and skin irritations, protective clothing and spectacles should be used. Employers should develop a training programme for all employees who are exposed to airborne concentrations of asbestos at or above the action level. The training programme must inform employees about the methods of recognizing asbestos and the health hazards of asbestos exposure; the relationship between asbestos and smoking in producing lung cancer; operations which could result in asbestos exposure; the importance of necessary protective controls to minimize exposure including, as applicable: engineering controls, work practices, respirators, housekeeping procedures, hygiene facilities, protective clothing, decontamination procedures, emergency procedures and waste disposal procedures; the purpose, proper use, and limitations of respirators; and the medical surveillance programme (6). Furthermore for construction workers who may be exposed to asbestos dust, hazards will be mitigated further by following advice issued to workers in the asbestos industry:


• be aware of the materials likely to contain asbestos, and potential risks;

• follow recommended working procedures, for example using hand tools for cutting and drilling asbestos products rather than mechanical tools;

• keep the working area clean; damp down dust before removal by vacuuming with specially-designed equipment; do not blow away debris with an airline;

• ensure waste material is properly collected in marked dustproof containers for safe disposal;

• wear protective clothing and a respirator where appropriate;

• wash or shower at the end of the working day;

• do not take working clothes home; and

• avoid smoking.

Employers have a duty to protect the workforce by taking all possible steps to minimize health risks. They should ensure that workers follow the guidelines above; they should provide suitable equipment and facilities (e.g. for showering), monitor exposure and when necessary arrange medical checks. Measures of this type have been adopted by the Indian government through the publication of 16 Indian Standards on Safety in the Use of Asbestos. In addition, the Indian government has established a Development Panel and the Asbestos Products Industry and an Expert Group to examine the feasibility of substituting alternative products (12).

Substitute materials

The substitution of asbestos should be considered where safe control cannot be achieved. Many materials have been developed as substitutes for asbestos based products, a large proportion of which use Man-made-mineral fibres (MMMFs). MMMFs, known as mineral wools or other types of fibres, (a term used is the United States of America to refer to mixtures of rock and slag wools) are amorphous glassy fibres made from molten slags, natural rocks such as basalt and borosilicate or calcium silicate glasses; chemically they are all amorphous silicates. Their use has increased greatly since the 1960s, partly due to a growing awareness of risks associated with asbestos. Applications of MMMFs are: reinforcement to glass reinforced cement; glass reinforced plastic and rubber; textiles and electrical insulation; insulating quilts, bats and boards; tiles, pipes and ductwork; acoustic insulation; high temperature thermal insulation e.g. lining refractory kilns; joints and gaskets; and as high efficiency air filters.

Studies however indicate that all respirable size MMMFs are not biologically inert and health hazards posed by them require thorough investigation. The International Agency for Research on Cancer (IARC) has indicated that (19):


• There is sufficient evidence for the carcinogenicity of glasswool and of ceramic fibres in experimental animals;

• There is limited evidence for the carcinogenicity of rockwool in experimental animals;

• There is inadequate evidence for the carcinogenicity of glass filaments and of slagwool in experimental animals;

• There is inadequate evidence for the carcinogenicity of glasswool and of glass filaments in humans;

• There is limited evidence for the carcinogenicity of rock-/slagwool in humans;

• No data were available on the carcinogenicity of ceramic fibres to humans.

Thus IARC (20), in accordance with its carcinogenic evaluation criteria (table 3), has concluded in an overall evaluation of the effects of glasswool, rockwool, slagwool and ceramic fibres that they are possibly carcinogenic to humans. On the other hand glass filaments are not classifiable as to their carcinogenicity. It should be noted that for carcinogens, in WHO guidelines, the values are based on an accepted risk of one additional cancer per year per hundred thousand exposed people. In countries where most deaths occurred from infections diseases, WHO considers it appropriate to compute safety standards on the basis of an accepted risk of one additional cancer per year per ten thousand exposed persons.

Table 3. IARC Carcinogenic evaluation criteria.



1 The agent (mixture) is carcinogenic to humans. The exposure circumstance entails exposures that are carcinogenic to humans

Used only when there is sufficient evidence of carcinogenicity in humans. Exceptionally, an agent (mixture) may be placed in this category when evidence in humans is less than sufficient but there is sufficient evidence of carcinogenicity in experimental animals and strong evidence in exposed humans that the agent (mixture) acts through a relevant mechanism of carcinogenicity.

2A The agent (mixture) is probably carcinogenic to human. The exposure circumstance entails exposures that are probably carcinogenic to humans

Used when there is limited evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in experimental animals. In some cases, an agent (mixture) may be classified in this category when there is inadequate evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in experimental animals and strong evidence that the carcinogenesis is mediated by a mechanism that also operates in humans. Exceptionally, an agent, mixture or exposure circumstance may be classified in this category solely on the basis of limited evidence of carcinogenicity in humans.

2B The agent (mixture) is possibly carcinogenic to humans. The exposure circumstance entails exposures that are possibly carcinogenic to humans

This category is used for agents, mixtures and exposure circumstances for which there is limited evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals. It may also be used when there is inadequate evidence of carcinogenicity in humans but there is sufficient evidence of carcinogenicity in experimental animals. In some instances, an agent, mixture or exposure circumstance for which there is inadequate evidence of carcinogenicity in humans but limited evidence of carcinogenicity in experimental animals together with supporting evidence from other relevant data may be placed in this group.

3 The agent (mixture or exposure circumstance) is not classifiable as to its carcinogenicity to humans.

This category is used most commonly for agents, mixtures and exposure circumstances for which the evidence of carcinogenicity is inadequate in humans and inadequate or limited in experimental animals. Exceptionally, agents (mixtures) for which the evidence of carcinogenicity is inadequate in humans but sufficient in experimental animals may be placed in this category when there is strong evidence that the mechanism of carcinogenicity in experimental animals does not operate in humans.

Agents, mixtures and exposure circumstances that do not fall into any other group are also placed in this category.

4 The agent (mixture) is probably not carcinogenic to humans.

Used for agents for which there is evidence suggesting lack of carcinogenicity in humans together with evidence suggesting lack of carcinogenicity in experimental animals. In some circumstances, agents for which there is inadequate evidence of carcinogenicity in humans but evidence suggesting lack of carcinogenicity in experimental animals, consistently and strongly supported by a broad range of other relevant data, may be classified in this group.


Source: IARC (1994). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Preamble, International Agency for Research on Cancer (IARC), Lyon, France.

Other related health hazards include skin, eye and upper - respiratory-tract irritations such as bronchitis (21). Occupational health hazards are due to improper exposure to MMMFs. According to IFBWW (21), most countries in the world treat MMMFs as nuisance dust and in most cases follow a standard of 10 mg/m3 of total dust or 5 mg/m3 for respirable dust. Examples of introduced more stringent fibre and gravimetric standards for MMMFs are as follows (21, 22):


• In Denmark, stationary workplaces must meet a 2. Of/ml fibre standard, and in non-stationary workplaces a 5 mg/m3 total dust standard is in effect;

• In Sweden, all work involving synthetic or inorganic fibres must meet a 1.0f/ml standard;

• In the United Kingdom of Great Britain and Northern Ireland a fibre standard of If/ml applies, as well as a total inhalable dust limit of 5 mg/m3;

• In Australia all work with MMMFs must meet a 0.5f/ml standard as well as a 2 mg/m3 respirable dust standard;

• In Germany there is no more TLV because MMMFs with diameter less than 1 μm are justifiably suspected of having carcinogenic potential; and

• In Canada, Alberta has adopted a limit of 1.0f/ml for fibrous glass and mineral wool and 0.5f/ml limit for refractory ceramic fibres, and a total dust standard of 5 mg/m3 for work with these materials also applies.

Other alternatives which do not contain mineral fibre such as metallic or ceramic products are often less available or considerably more expensive. The possible hazards posed by fibrous materials may have to be considered in relation to these other disadvantages in selecting components. For new buildings, non-fibrous alternatives to asbestos should be considered first. Whenever MMMFs substitutes are considered, and as in the case of asbestos, appropriate work practices, engineering, and administrative control measures should aim at controlling the exposure of workers to airborne dust and fibres. Substitute materials and non-fibrous alternatives are suggested in table 4.

Table 4. Examples of asbestos-based materials, MMMF-based substitutes and alternatives

Asbestos-based material

MMMFs-based substitutes


asbestos based thermal insulation

glass fibre or rock-wool quilt, rock-wool bats

cellulose quilt, expanded or extruded polystyrene board polystyrene beads

asbestos pipe lagging

mineral-wool lagging or preformed sections

foamed rubber or polystyrene sections

asbestos cement or asbestos filled double walled metallic flues

mineral fibre filled double walled metallic flues

masonry chimney, preformed concrete block flue, double walled metallic air filled flue

asbestos based acoustic insulation

mineral fibre reinforced sprayed plaster

foamed rubber or polystyrene, textiles, textured plaster

fire-proof lining sheets

glass-reinforced cement board, calcium silicate based board

multi-layer plasterboard

sprayed asbestos fire proofing


intumescent coating

asbestos cement roofing sheets

fibre reinforced calcium silicate sheets, glass reinforced cement, glass reinforced plastic

vegetable-fibre cement sheets, profiled steel, sheet metal (zinc, aluminium etc.)

asbestos-based roofing felt

glass fibre based felt

polyester-based or pitch polymer felts

asbestos cement slates

glass reinforced cement

natural slate, clay or concrete tiles, PVA cement slates

asbestos cement water storage tanks

glass reinforced cement

polythene, polypropylene, galvanised mild steel

asbestos cement rainwater goods

glass reinforced plastic

cast iron, aluminium, uPVC

asbestos cement eaves, soft board

glass reinforced cement board, calcium silicate board

softwood, plywood, PVA cement board

asbestos fibre/vinyl floor tile or sheet

mineral fibre/vinyl tile or sheet

thermoplastic tiles, linoleum, clay tiles


Source: Spence, R. J. S., Cambridge Architectural Research Limited (UK), Building Materials and Health (Unpublished draft report prepared for the United Nations Centre for Human Settlements (Habitat), September 1994).
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