Asbestos extent

The extent of substitution of magnesium and siUcon by other cations in the chrysotile stmcture is limited by the stmctural strain that would result from replacement with ions having inappropriate radii. In the octahedral layer (bmcite), magnesium can be substituted by several divalent ions, Fe ", Mn, or Ni ". In the tetrahedral layer, siUcon may be replaced by Fe " or Al ", leaving an anionic vacancy. Most of the other elements which are found in vein fiber samples, or in industrial asbestos fibers, are associated with interstitial mineral phases. Typical compositions of bulk chrysotile fibers from different locations are given in Table 3. 

The choice of a particular mining method depends on a number of parameters, typically the physical properties of the host matrix, the fiber content of the ore, the amount of sterile materials, the presence of contaminants, and the extent of potential fiber degradation during the various mining operations (33). However, most of the asbestos mining operations are of the open pit type, using bench drilling techniques. 

Asbestos fibers have also been widely used for the fabrication of papers and felts for flooring and roofing products, pipeline wrapping, electrical insulation, etc. Asbestos textiles, comprising yam, thread, cloth, tape, or tope, also found wide apphcation in thermal and electrical insulation, friction products in brake or clutch pads, etc. In recent years, some of these appHcations have decreased to various extents, although others remain fairly active, typically in friction materials. 

The search for asbestos replacement materials is obviously an ongoing process and further developments in this area are to be expected. The extent of substitution of asbestos fibers by other fibers or other materials has been limited by several factors, typically the availabiHty of adequate replacement materials, the cost performance ratio of such materials, and the uncertainty of long-term health risks of these replacement materials. From the data currendy available, it may be estimated that between 10—20% of the industrial consumption of asbestos fibers was diverted to other materials during the 1980s. 

In order to define the extent of emissions from automotive brakes and clutches, a study was carried out in which specially designed wear debris collectors were built for the dmm brake, the disk brake, and the clutch of a popular U.S. vehicle (1). The vehicle was driven through various test cycles to determine the extent and type of brake emissions generated under all driving conditions. Typical original equipment and aftermarket friction materials were evaluated. Brake relines were made to simulate consumer practices. The wear debris was analyzed by a combination of optical and electron microscopy to ascertain the asbestos content and its particle size distribution. It was found that more than 99.7% of the asbestos was converted to a nonfibrous form and... 

Total frequencies of environmental illness are difficult to measure. When causes can be identified, however, scientists observe that frequencies of occurrence of a particular illness vary directly with the severity and extent of exposure. Particularly frequent in the workplace are skin lesions from many different causes and pulmonary diseases related to the inhalation of various dusts, such as coal dust (black lung), cotton dust (brown lung), asbestos fibers (asbestosis), and silica dust (silicosis). Environmental agents can also cause biological effects without overt clinical illness (for example, chromosome damage from irradiation). 

Deactivation and D D actions can range from stabilization of multiple hazards at a single site or facilities containing chemical or radioactive contamination, or both, to routine asbestos and lead abatement in a nonindustrial structure. Strategies include programs that meet compliance objectives, protect workers, and make certain that productivity and cost-effectiveness are maintained. The content and extent of health and safety-related programs should be proportionate to the types and degrees of hazards and risks associated with specific operations. 

Considerable inertia in established practices can be observed everywhere, a tediousness and resistance to change, against which the substitution of hazardous substances has to struggle. Although in many cases the problems of hazardous substances are evident to a large extent, and although substitutes are available, indeed available for many areas of application, the substitution process is not progressing. The substitution of asbestos was a typically extremely tedious process (cf chapter 2.2). 

Another problem is the extent of regulative measures. On the one hand, the use of asbestos is now almost completely banned in the European Union and in many other industrialised and economically thriving countries. On the other hand, more than 2 milhon tons of asbestos are extracted and consumed globally every year. A uniform global hazardous substances pohcy evidently does not exist yet. 

Industrial processes, such as mUling and mining, construction work, and the burning of wood or fossil fuel, generate particulates that can be directly toxic or can serve as vectors for the transfer of bound material, such as sulfuric acid, metals, and hydrocarbons, into the lungs. Natural products such as pollen, anthrax spores, and animal dander can elicit toxic reactions on inhalation or skin contact. The inhalation of asbestos, silica, or coal dust can cause pneumoconiosis, which may develop into serious lung disease. The size of the particle, ventilatory rate, and depth of breathing will determine the extent of pulmonary deposition. 

Recognizing the applicability of XRD to occupational health chemistry, Lennox and Leroux (1) suggested a number of chemical species which would be suitable for XRD analysis arsenic trioxide, beryllium oxide, mica, vanadium oxides, calcium fluoride in ceramic materials, as well as a number of organics such as DDT, lindane and chlordane. Unfortunately, the general application of XRD to the quantitation of industrial hygiene samples has not been realized and the majority of these analyses are restricted to free silica and to a lesser extent asbestos and talc. 

The main reaction is the stoichiometric one, AgO + CO —> Ag + CO2, although some catalytic action is also evident. The silver peroxide is supported on asbestos in the form of small cubes or cylinders prepared by extrusion. The preparation does not react with carbon dioxide to an appreciable extent and is much more stable than hopcalite in the presence of water vapor. Because of its relative stability to water vapor, it may be used in a gas mask canister without the incorporation of drying agents, such as are necessary in hopcalite canisters. 

Since the formulation of his concepts in 1939 Kobozev has carried out many investigations in the attempt to verify their general validity. In the decomposition of H202 and the oxidation of Na2SCh, the specific effect (173) of small amounts of iron (0.0005 to 40%) added to copper on carbon and the converse in which small amounts of copper were added to iron on carbon were studied. The activity of these catalysts was very effectively promoted by these additives, the extent of promotion being proportional to the concentration of the additives. The catalytic synthesis of ammonia by iron supported on carbon or asbestos was also studied. The results of this study and similar studies of catalytic... 

In almost all the failures, including failure of the service saddle on an asbestos-cement 10-inch water pipe, corrosion from the soil side was to great extent responsible for the failures. 

Considerable energy must be involved in pulling apart the asbestos fibers during the impact energy used in overcoming frictional type forces, forces required to pull individual fibers away and past others. The extent of this mechanism is dependent on the asbestos fiber bundles not being thoroughly wet by the matrix since the better wet open fibers are fractured at the matrix fracture surface. 

As a result, to date epidemiological studies of pesticide exposures have only been indicative of the presence of elevated health risks. Quantitative studies contributing to evidence on exposure-response relationships which could be used for quantitative risk assessment purposes are not widely available. This implies that the epidemiological potential has not been explored to its limits, as has been done for certain other agents such as asbestos and lead, for which present legislation has been based, to a large extent, on quantitative evidence of health risks in humans obtained from epidemiological studies. 

Tremolite-actinolite is present in or around some deposits of chrysotile asbestos. However, levels of amphibole asbestos in commercial chrysotile were not reported. Tremolite is a contaminant in talc from New York and California, but the extent and fibrosity of the tremolite is unclear (DOT 1980 Wagner et al. 1982c American Thoracic Society 1990). The tremolite in some talc Ifom Califomia has been described as flake-like and that from New York as having fine fibers (Wagner et al. 1982a). Some tremolite in the chrysotile Ifom Quebec has been described as having coarse fibers. A British survey of talc powders used for various purposes identified 3 out of 24 samples as containing tremolite. Ten of 20 samples of cosmetic talc purchased in New York City between 1971 and 1975 contained 1-14% (w/w) of fibrous tremolite and... 

Pinkerton KE, Plopper CG, Mercer RR, et al. 1986. Airway branching patterns influence asbestos fiber location and the extent of tissue injury in the pulmonary parenchyma. Lab Invest 55 688-695. 

Tremolite asbestos has only rarely been found in commercially mined deposits. Some tremolite asbestos has been mined in South Africa, India, Maryland, and South Korea, but it has never been a nationally important commercial source of asbestos in the United States. (Ross 1981). The extent of tremolite asbestos mining was small in Powhatan and Pylesville, Maryland, where it occurs with anthophyllite asbestos in ultramafic rocks (Ross 1981). In South Africa, tremolite asbestos was mined in the early twentieth century, but most amphibole asbestos recently mined in South Africa is amosite or crocidolite... 

ASTM E 84 Steiner Tunnel Test. This test, which uses very large samples (20 ft x 20 1/4 in.) is referenced in all model building codes for evaluating flame spread and smoke emission of foam plastic insulation. The test apparatus consists of a chamber or tunnel 25 ft. long and 17 3/4 X 17 5/8 in. in cross section, one end of which contains two gas burners. The test specimen is exposed to the gas flame for ten minutes, while the maximum extent of the flame spread and the temperature down the tunnel are observed through windows. Smoke evolution can also be measured by use of a photoelectric cell. The flame spread and smoke evolution are reported in an arbitrary scale for which asbestos and red oak have values of 0 and 100, respectively. More highly fire-retardant materials have ratings of 0-25 by this method. 

The potential for unusual health effects of chemical mixtures due to the interaction of chemicals or their metabolites (e.g., metabolites of trichloroethylene and benzene) in or with the biosystem constitutes a real issue in the public health arena. However, toxicity testing to predict effects on humans has traditionally studied one chemical at a time for various reasons convenient to handle, physiochemical properties readily defined, dosage could easily be controlled, biologic fate could easily be measured, and relevant data were often available from human occupational exposures. Chemicals are known to cause disease for example, arsenic and skin cancer, asbestos and lung cancer, lead and decrements of IQ, and hepatitis B predisposes to aflatoxin-induced liver cancer but the link between the extent of human exposure to even well-defined chemical mixtures and disease formation remains relatively unexplored, but of paramount importance to public health. 

The major sources of air pollutants found in buildings are described below. However, the mere presence of a potential contaminant source does not necessarily mean that exposure will ensue. This is because the extent of exposure, if any, often depends on the physical nature of a source or the manner in which it is used an example of this is asbestos, as will be discussed later. Furthermore, the health significance of exposure to indoor pollutants may not always be clear. While many of these toxicants may have adverse effects under exposure conditions found in occupational and other environments, often much less is known about biological responses with prolonged exposures at concentrations common in indoor environments. 

Special consideration must be given to physical characteristics in the choice of catalyst support. Since asbestos fibers are not porous to any extent, catalysts supported on asbestos are held in the inter-fibrilar spaces. When asbestos is used, precautions must be taken to prevent the felt-like mass from compacting and increasing the resistance to gas flow. For this purpose, asbestos-supported catalysts are used in numerous thin layers, each layer on a separate perforated plate. Despite its resistance to temperature effects, asbestos is not favored as a support and the more rigid materials preferred. 

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