Реферат: Asbestos Essay Research Paper Asbestos is the
Asbestos Essay, Research Paper
Asbestos is the only natural inorganic fibrous material that has attained commercial importance, and particularly in the last twenty years. The current period after World War II has witnessed a vigorous development in all technological areas where asbestos plays a part (Oesper 1). The word asbestos is derived from a Greek adjective meaning inextinguishable. The “miracle mineral” as it was referred to by the Greeks, was admired for its soft and plain properties, as well as its ability to withstand heat. Asbestos was spun and woven into cloth as the same manner as cotton. It was also utilized for wicks in sacred lamps. In technology and industry the term asbestos is applied to the fibrous crystalline varieties of five distinct natural silicates. Only those asbestoses with fiber lengths that permit their textile processing were really desired. Asbestos is a naturally occurring mineral. It is distinguished from other materials by the fact that its crystals form long, thin fibers. The primary sites of commercial production of asbestos are: Canada, the Soviet Union, and South America. Asbestos is also mined commercially in the United States. An asbestos fiber is defined as a particle which has a length to width ratio equal to or greater than 3:1 and a length greater than 5 um. Asbestos was first used in the United States in the early 1900’s, to insulate steam engines. But until the early 1940’s, asbestos was not used extensively. However, after World War II, and for the next thirty years, people who constructed and renovated schools and other public buildings used asbestos and asbestos -containing materials (ACM) extensively. They used ACM primarily to fireproof, insulate, soundproof, and decorate. The Environmental Protection Agency (EPA) estimates that there are asbestos containing materials in most of the nation’s approximately 107,000 primary and secondary schools and 733,000 public and commercial buildings (Asbestos in Buildings 2-5). These minerals are hydrated silicates of magnesium with variable amounts of metals. Three varieties have commercial importance: chrysotile (white), amosite (brown) and crocidolite (blue). As a group, these minerals have good thermal and electrical insulating properties, good tensile strength, low chemical activity and do not burn. As a result, they were used in over 4000 products. Chrysotile asbestos is mined in Canada and has been the most commonly used. The use of crocidolite asbestos has been banned since 1978. We have learned to depend on these mineral fibers. Fire does not burn them. Alkalis do not eat them. Water does not destroy them. Vermin do not attack them. They do not decay, rot, or corrode. Surely asbestos is a magic mineral (Strack 54). Serpentine rock often contains chrysotile asbestos, especially near fault zones. Serpentine rock is abundant in the Sierra foothills, the Klamath Mountains, and Coast Ranges. Serpentine rock is typically grayish-green to bluish-black in color and may have a shiny appearance. Asbestos is not found in all serpentine rock or fault zones, but when it does occur, it is typically present in amounts ranging from less than 1% up to about 25%, and sometimes more. Asbestos is released from serpentine rock when it is broken or crushed. This can happen when cars drive over unpaved roads or driveways which are surfaced with serpentine rock, when land is graded for building purposes, or at quarrying operations. It is also released naturally through weathering and erosion. Once released from the rock, asbestos can become airborne and may stay in the air for long periods of time (Oespert 98). Asbestos has been used in hundreds of products. Collectively, these are frequently referred to as asbestos-containing material. Asbestos gained widespread use because it is plentiful, readily available, and low in cost. Because of its unique properties: fire resistant, high tensile strength, poor heat and electric conductivity, and generally impervious to chemical attacks, asbestos proved well-suited for many uses in the construction trades (Pierce). One of the most common uses for asbestos is as fireproofing material. It was sprayed on steel beams, columns, and decking that were used in construction of multistoried buildings. This application prevented these structural members from warping or collapsing in the event of a fire. Asbestos is also added to a variety of building materials to enhance strength. It is found in concrete and concrete-like products. Asbestos-containing cement products generally contain Portland cement, aggregate, and asbestos fibers. The asbestos content may vary up to 50 percent by weight depending on the use of the product. Asbestos cement products are used as siding and roofing shingles; as wallboard; as corrugated and flat sheets for roofing, cladding, and partitions; and as pipes. Asbestos has also been added to asphalt, vinyl, and other materials to make products like roofing felts, exterior siding, floor tiles, joint compounds, and adhesives (Med. University of SC.). Fibers in asbestos cement, asphalt, and vinyl are usually firmly bound in the cement and will be released only if the material is mechanically damaged, for example by drilling, cutting, or sanding. Roofing shingles and siding may also show slow deterioration due to weathering. As an insulator, asbestos received widespread use for thermal insulation and condensation control. It was usually spray applied, trowel applied, or factory installed on or within equipment. Asbestos is also a common component of brake linings and clutch faces. Asbestos proved valuable as a component of acoustical plaster. The material was applied by trowel or by spraying on ceilings and sometimes walls. It varies in color from white to gray – rarely was it painted as a noticeable loss of acoustical value occurs. Similarly as a decorative product, asbestos was mixed with other materials and sprayed on ceilings and walls to produce a soft, textured appearance (Medical University of South Carolina). Although asbestos textile products rand below asbestos cement, frictional materials, and flooring compositions in money value, they represent the main characteristic from this unique inorganic fibrous material, the only one of its kind occurring in nature in quantities sufficient for commercial purposes. The United States is the largest such supplier and produces around 40 million dollars annually (Oesper 101). Asbestos has been used in the United States since the early 1900’s, however, asbestos is no longer allowed as a constituent in most home products and materials. Many older buildings, schools, and homes still have asbestos containing products. Therefore, laws are in place to protect citizens when these buildings are renovated or demolished (Peters 45). All types of asbestos are hazardous and may cause lung disease and cancer. Health risks to people are dependent upon their exposure to asbestos. The longer a person is exposed to asbestos and the greater the intensity of the exposure, the greater the chances for a health problem. Asbestos-related disease, such as lung cancer, may not occur for decades after breathing asbestos fibers. Cigarette smoking increases the risk of lung cancer from asbestos exposure (Peters 126). Asbestos-containing material is dangerous if the asbestos fibers can be released. Once they are floating freely in the air, asbestos fibers can be inhaled and cause disease. Some ACM can easily be crumbled by hand pressure. This soft or loosely-bound material is called “friable” asbestos. Friable ACM is the greatest health concern because it can easily release fibers in place begin to deteriorate, the likelihood of fiber release is even greater. Examples of friable asbestos-containing materials are fireproofing on structural beams, sprayed-on asbestos ceiling insulation and trowelled-on acoustical insulation.
Hard asbestos-containing material, such as vinyl floor tile, in which asbestos fibers are firmly bound or encased, does not generally create exposure problems. However, even non-friable ACM can release fibers and present a hazard if it is sanded, cut, ground or disturbed in some other way. Therefore, any material that contains asbestos has the potential to release fibers and become hazardous (Peter 52). The Environmental Protection Agency (EPA) and others distinguish between friable and non-friable forms of ACM. Friable ACM contains more than 1% asbestos. Other things being equal, friable ACM is thought to release fibers into the air more readily; however, many types of non-friable ACM can also release fibers if disturbed. While it is often possible to suspect that a material or product contains asbestos by visual determination, actual determination can only be made by instrumental analysis. The EPA requires that the asbestos content of suspect materials be determined by collecting bulk samples and analyzing them by polarized light microscopy (PLM). The PLM technique determines both the percent and type of asbestos in the bulk material(Asbestos in Buildings 1-5). As reported in a survey recorded my the National Survey of Asbestos-Containing Friable Materials, rental residential buildings have the highest incidence of sprayed or troweeled-on asbestos containing friable material (2-6). After reviewing a report on asbestos in a local Procter and Gamble facility, the precautions taken are very evident. The most common way for asbestos to enter the body is though breathing. Once inhaled, the asbestos fibers do not ever escape and it is thought that even small amounts can eventually produce lung cancer or mesothelioma, a lung-lining cancer. Another asbestos disease, asbestosis, requires much larger amounts of asbestos in the lungs than could be produced in a residence or a workplace that is not involved in the asbestos business. Asbestos cancers have a long latency period, 20-30 years, so that young people have a greater chance to be affected in their lifetime than older people (Pierce). Larger fibers usually get trapped in the nose hairs or in the mucous along the breathing passageways. However, some asbestos fibers are so small that they can bypass these body defense mechanism and get deep into the lungs. Asbestos can also enter the digestive tract when you eat or smoke in a contaminated area. Asbestos does not pass through the skin. Asbestosis was the first clearly demonstrated adverse effect of asbestos in man. It is a nonmalignant fibrotic lung disease caused by inhalation of asbestos fibers. These fibers in the respiratory system reduce the ability of the lungs to extract sufficient oxygen from the air. It is associated with exposures to high concentrations of asbestos fibers (Pierce). Bronchogenic carcinoma is a malignant tumor which usually occurs in the lower lobes of the lungs. While asbestos exposure results in a small but significant risk of lung cancer, cigarette smoking in conjunction with asbestos exposure leads to a total cancer risk which is many times greater than that from either asbestos exposure or smoking alone. Mesothelioma is a rare cancer of the linings of the chest and abdominal cavities. Exposures of only a few weeks duration to asbestos fibers have resulted in this disease. A unique feature of the disease is the long period, generally 20-30 years, between first exposure to asbestos and the appearance of a tumor. Asbestos is increasingly suspected to have a role in the development of cancers of the larynx and pharynx (Pierce). Once asbestos is determined to be present in a material, several options of dealing with the material are possible. The first option would be to leave the material as is and untouched. This is often the option of choice for non-friable materials, materials which are in nonpublic areas and therefore only affect a few workers trained in asbestos hazards, and materials which are isolated from human contact. A second option is encapsulation, which means to enclose the material without removing it. The enclosure can consist of a constructed barrier, for instance, of finished drywall over a surface coating, or of painted canvas over pipe insulation. Alternatively, the encapsulation can be a sprayed polymer of two types: penetrating encapsulant, which soaks into the material it is sprayed on, and bridging encapsulant, which only seals the surface, like paint. Even though the release of fiber is minimized or eliminated with encapsulation, the asbestos is still present, and the potential for fiber release always exists. The third option is removal, in which the asbestos-containing material is scraped off, chopped off or otherwise gotten rid and taken out of the building. Preparation of the building so as to prevent contamination of the premises is extensive and disposal of the material is expensive, so removal is the least economical of the three options. It has the advantage that the asbestos is for the most part gone, except those parts of the building that are inaccessible (Asbestos in Buildings 3-1). The only way to know if a product contains asbestos is to send a piece of the suspect material to a qualified laboratory, called a bulk sample. Only certain kinds of microscopes can be used to analyze the sample: a polarizing light microscope or an electron microscope (Pierce). The U.S. Environmental Protection Agency (EPA) has established a very broad ban on the manufacture, processing, importation, and distribution of materials or products that contain asbestos. These regulations were initiated in 1990, and was put in full force in 1997. This ban will result in elimination of asbestos in insulation, brakes, floor and ceiling tiles, cement, paper, and nearly all other asbestos-containing materials. Second, EPA has established regulations that require school systems to investigate whether asbestos exposure is a problem inside their school buildings, and if so, to reduce or eliminate the exposure, either by removing the asbestos or by covering it up so it cannot get into air. In addition, EPA provides guidance and support for reducing asbestos exposure in other public buildings. Third, EPA regulates the release of asbestos from factories and during building demolition or renovation to prevent asbestos from getting into the environment. EPA also regulates the disposal of waste asbestos materials or products, requiring these to be placed only in approved locations. Fourth, EPA has proposed a limit of 7 million fibers per liter on the concentration of long fibers that may be present in drinking water (Asbestos in Buildings 5-4). BibliographyAsbestos in Buildings: A National Survey. Washington, D.C.: Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, US Environmental Protection Agency, 1984.Medical University of South Carolina. Asbestos Background Information. [http://www.musc.edu/DEHS/AsbestosInfo.htm]. Oesper, Ralph. Asbestos Fundamental. New York: Chemical Publishing Company, Inc., 1963Peter, George. Asbestos Review and Update. New York: Garland Law Publishing, 1987.Pierce, Larry. Information about Asbestos. [http://www.fiberq.com/Info/Asbestos.html]; 1989. Procter and Gamble Asbestos Control Program Manual. 1988.Strack, Lilian. Asbestos, A Magic Mineral. London: Harpers and Brothers, 1941.