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Asbestos fiber


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This PPT discuss in detail about the Asbestos Fiber its Pro & Cons. It also explains the laws which were stated in banning the asbestos usage in friction industry

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Asbestos fiber

  1. 1. Presentation on Asbestos Fiber
  2. 2. ASBESTOS  Asbestos (pronounced /æsˈbɛstəs/ or /æzˈbɛstəs/) is a set of six naturally occurring silicate minerals which all have in common their eponymous asbestiform habit: long (roughly 1:20 aspect ratio), thin fibrous crystals.  Asbestos mining began more than 4,000 years ago, but did not start large- scale until the end of the 19th century when manufacturers and builders used asbestos because of its desirable physical properties: sound absorption, average tensile strength, its resistance to fire, heat, electrical and chemical damage, and affordability. It was used in such applications as electrical insulation for hotplate wiring and in building insulation . When asbestos is used for its resistance to fire or heat, the fibers are often mixed with cement or woven into fabric or mats.  The prolonged inhalation of asbestos fibers can cause serious illnesses including malignant lung cancer mesothelioma asbestosis (a type of pneumoconiosis. The trade and use of asbestos have been restricted or banned in many jurisdictions.
  3. 3. Fibrous tremolite asbestos on muscovite
  4. 4. INTRODUCTION  Asbestos is the term used for the fibrous form of a number of naturally occurring silicate minerals that have been exploited commercially for their useful properties of:  flexibility  high tensile strength  incombustibility  low thermal conductivity and  resistance to chemical attack  There are six minerals included in this definition; one, chrysotile, is in the serpentine group of minerals, while the others, including amosite, crocidolite, anthophyllite, actinolite and tremolite belong to the amphibole group of minerals.
  5. 5. TYPES OF ASBESTOS  The three types of asbestos that have found significant industrial uses are amosite (brown asbestos), chrysotile (white asbestos) and crocidolite (blue asbestos). None of these minerals is found in commercial quantities in the UK, the bulk of the material that were used by industry were imported from Canada or South Africa.  In total, over 5 million tones of asbestos were imported into the UK.  The maximum importation of asbestos into the UK occurred between 1970 and 1975; thereafter importation has declined and for the amphiboles it has ceased completely. The figure shows the amount of the three common types of asbestos imported into the UK during the last century.
  6. 6. PROPERTIES  The physical and chemical properties of asbestos determined its uses and commercial value. The very fine fibers of chrysotile and crocidolite were ideal for textile products. Their thermal stability made the asbestos minerals useful in friction products and, together with their low thermal conductivity, in insulation materials. Asbestos cements made with chrysotile asbestos were durable materials because of the chemical bonding of the lime with the surface of the fibers.  The use of asbestos was banned in Britain in 1999, but there are still a great deal of asbestos-containing materials in buildings and industrial plant
  7. 7. FORMULA  Category Mineral Formula (repeating unit)Mg3Si2O5(OH)4
  8. 8. CTD., Asbestos
  9. 9. BLUE ASBESTOS Blue Asbestos (Crocidoite) from Wittenoom Western Australia. The ruler is 1 cm.
  10. 10. CTD., Blue asbestos, teased to show the fibrous nature of the mineral (from mine at Wittenoom, Western Australia)
  13. 13. SEM OF ASBESTOS FIBRES Asbestos fibers (SEM micrograph)
  14. 14. CHEMISTRY  Individual asbestos fibers are invisible to the unaided human eye because their size is about 3– 20 µm wide and can be as slim as 0.01 µm. Human hair ranges in size from 17 to 181 µm in breadth.[68] Fibers ultimately form because when these minerals originally cooled and crystallized, they formed by the polymeric molecules lining up parallel with each other and forming oriented crystal lattices. These crystals thus have three cleavage planes, and in this case, there are two cleavage planes which are much weaker than the third. When sufficient force is applied, they tend to break along their weakest directions, resulting in a linear fragmentation pattern and hence a fibrous form. This fracture process can keep occurring and one larger asbestos fiber can ultimately become the source of hundreds of much thinner and smaller fibers.  When fibers or asbestos structures from asbestos containing materials (ACM) become airborne, the process is called primary release. Primary release mechanisms include abrasion, impaction, fallout, air erosion, vibration, and fire damage. Secondary release occurs when settled asbestos fibers and structures are resuspended as a result of human activities. In unoccupied buildings or during unoccupied periods, fiber release typically occurs by fallout or is induced by vibration or air erosion.[69]  Friability of a product containing asbestos means that it is so soft and weak in structure that it can be broken with simple finger crushing pressure. Friable materials are of the most initial concern because of their ease of damage. The forces or conditions of usage that come into intimate contact with most non-friable materials containing asbestos are substantially higher than finger pressure.
  15. 15. IDENTIFICATION AND ASSESSMENT  A fiber cannot be identified or ruled out as asbestos, either using the naked eye or by simply looking at a fiber under a regular microscope. The most common methods of identifying asbestos fibers are by using polarized light microscopy (PLM) or transmission electron microscopy (TEM). PLM is less expensive, but TEM is more precise and can be used at lower concentrations of asbestos.  If asbestos abatement is performed, completion of the abatement is verified using visual confirmation and may also involve air sampling. Air samples are typically analyzed usingphase contrast microscopy (PCM). PCM involves counting fibers on a filter using a microscope. Airborne occupational exposure limits for asbestos are based on using the PCM method.  The American Conference of Governmental Industrial Hygienists has a recommended Threshold Limit Value (TLV) for asbestos of 0.1 fibers/mL over an 8 hour shift. OSHA in the United States and occupational health and safety regulatory jurisdictions in Canada use 0.1 fibers/mL over an 8 hour shift as their exposure limits.[70]
  16. 16. ENVIRONMENTAL ASBESTOS  Asbestos can be found naturally in the air outdoors and in some drinkable water, including water from natural sources.[74] Studies have shown that members of the general (non-occupationally exposed) population have 10,000-999,999 asbestos fibers in each gram of dry lung tissue, which translates into millions of fibers and tens of thousands of asbestos bodies in every person's lungs.[75]  Asbestos from natural geologic deposits is known as "naturally occurring asbestos" (NOA). Health risks associated with exposure to NOA are not yet fully understood, and current US federal regulations do not address exposure from NOA. Many populated areas are in proximity to shallow, natural deposits which occur in 50 of 58 California counties and in 19 other US states. In one study, data was collected from 3,000 mesothelioma patients in California and 890 men with prostate cancer, a malignancy not known to be related to asbestos. The study found a correlation between the incidence of mesotheliomas and the distance a patient lived from known deposits of rock likely to include asbestos; the correlation was not present when the incidence of prostate cancer was compared with the same distances. According to the study, risk of mesothelioma declined by 6% for every 10 km (6.2 mi) that an individual had lived away from a likely asbestos source.[76]
  17. 17. CTD.,  Portions of El Dorado County, California are known to contain natural amphibole asbestos formations at the surface.[76][77] The USGS studied amphiboles in rock and soil in the area in response to an EPA sampling study and subsequent criticism of the EPA study. The EPA study was refuted by its own peer reviewers and never completed or published. The study found that many amphibole particles in the area meet the counting rule criteria used by the EPA for chemical and morphological limits, but do not meet morphological requirements for commercial-grade-asbestos. The executive summary pointed out that even particles that do not meet requirements for commercial-grade-asbestos may be a health threat and suggested a collaborative research effort to assess health risks associated with "Naturally Occurring Asbestos."  However, the main criticism pointed at EPA was that their testing was conducted in small isolated areas of El Dorado where there were no amphibole asbestos deposits, thus the language regarding amphibole, nonfibrous "particles". Actual surface amphibole deposits in residential areas were ignored for testing purposes. Because of this, no final findings were published by ATSDR.[78]
  18. 18. CTD.,  A great deal of Fairfax County, Virginia was also found to be underlaid with tremolite. The county monitored air quality at construction sites, controlled soil taken from affected areas, and required freshly developed sites to lay 6 inches (150 mm) of clean, stable material over the ground.[76]  Globally, collected samples from Antarctic ice indicate Chrystoile asbestos has been a ubiquitous contaminant of the environment for at least 10,000 years. Snow samples in Japan have shown ambient background levels are one to two orders of magnitude higher in urban than in rural areas. Higher concentrations of airborne asbestos fibers are reported in urban areas where there is more ACM (asbestos containing materials) and mechanisms of release (vehicles braking and weathering of asbestos cement materials); concentrations in the range of 1–20 ng/m^3 have been reported. Fibers longer than 5μm are rarely found in rural areas. Ambient concentrations using TEM analysis have been based on mass measurements.[69]
  19. 19. HISTORY OF HEALTH CONCERNS AND REGULATION Until 1900  The 1st century AD, Greeks and Romans are claimed to have observed that slaves involved in the weaving of asbestos cloth were afflicted with a sickness of the lungs,[79]although this is not confirmed by examination of primary sources.[16]  Early concern in the modern era on the health effects of asbestos exposure can be found in several sources. Among the earliest were reports in Britain. The annual reports of the Chief Inspector of Factories in 1898 included a report from Lucy Deane which stated that asbestos had "easily demonstrated" health risks.[80][81]  At about the same time, what was probably the first study of mortality among asbestos workers was reported in France.[82] While the study describes the cause of death aschalicosis, a generalized pneumoconiosis, the circumstances of the employment of the fifty workers whose death prompted the study suggest that the root cause was asbestos or mixed asbestos-cotton dust exposure.
  20. 20. CTD., 1900s–1910s  Further awareness of asbestos-related diseases can be found in the early 1900s, when London doctor H. Montague Murray conducted a post mortem exam on a young asbestos factory worker who died in 1899. Dr. Murray gave testimony on this death in connection with an industrial disease compensation hearing. The post-mortem confirmed the presence of asbestos in the lung tissue, prompting Dr. Murray to express as an expert opinion his belief that the inhalation of asbestos dust had at least contributed to, if not actually caused, the death of the worker.[83]  The record in the United States was similar. Early observations were largely anecdotal in nature and did not definitively link the occupation with the disease, followed by more compelling and larger studies that strengthened the association. One such study, published in 1918, noted:  All of these processes unquestionably involve a considerable dust hazard, but the hygienic aspects of the industry have not been reported upon. It may be said, in conclusion, that in the practice of American and Canadian life insurance companies, asbestos workers are generally declined on account of the assumed health-injurious conditions of the industry.[84]
  21. 21. CTD., 1920s–1930s  Widespread recognition of the occupational risks of asbestos in Britain was reported in 1924 by a Dr. Cooke, a pathologist, who introduced a case description of a 33-year-old female asbestos worker, Nellie Kershaw, with the following: "Medical men in areas where asbestos is manufactured have long suspected the dust to be the cause of chronic bronchitis and fibrosis ..."[85] Dr. Cooke then went on to report on a case in 1927 involving a 33-year-old male worker who was the only survivor out of ten workers in an asbestos carding room. In the report he named the disease "asbestosis".[86]  Dr. Cooke's second case report was followed, in the late 1920s, by a large public health investigation (now known as the Merewether report after one of its two authors) that examined some 360 asbestos-textile workers (reported to be about 15% of the total comparable employment in Britain at the time) and found that about a quarter of them suffered from pulmonary fibrosis.[87] This investigation resulted in improved regulation of the manufacturing of asbestos-containing products in the early 1930s. Regulations included industrial hygiene standards, medical examinations, and inclusion of the asbestos industry into the British Workers' Compensation Act.[88]  The first known U.S. workers' compensation claim for asbestos disease was in 1927.[89] In 1930, the first reported autopsy of an asbestosis sufferer was conducted in the United States and later presented by a doctor at the Mayo Clinic, although in this case the exposure involved mining activities somewhere in South America.[90]
  22. 22. CTD.,  In 1930, the major asbestos company Johns-Manville produced a report, for internal company use only, about medical reports of asbestos worker fatalities.[91] In 1932, a letter from U.S. Bureau of Mines to asbestos manufacturer Eagle-Picher stated, in relevant part, "It is now known that asbestos dust is one of the most dangerous dusts to which man is exposed."[92]  In 1933, Metropolitan Life Insurance Co. doctors found that 29% of workers in a Johns-Manville plant had asbestosis.[91] Likewise, in 1933, Johns-Manville officials settled lawsuits by 11 employees with asbestosis on the condition that the employees' lawyer agree to never again "directly or indirectly participate in the bringing of new actions against the Corporation."[92] In 1934, officials of two large asbestos companies, Johns-Manville and Raybestos-Manhattan, edited an article about the diseases of asbestos workers written by a Metropolitan Life Insurance Company doctor. The changes downplayed the danger of asbestos dust.[92] In 1935, officials of Johns-Manville and Raybestos-Manhattan instructed the editor of Asbestos magazine to publish nothing about asbestosis.[92] In 1936, a group of asbestos companies agreed to sponsor research on the health effects of asbestos dust, but required that the companies maintain complete control over the disclosure of the results.[91]
  23. 23. CTD., 1950s  In 1951, asbestos companies removed all references to cancer before allowing publication of research they sponsored.[94] In 1952, Dr. Kenneth Smith, Johns-Manville medical director, recommended (unsuccessfully) that warning labels be attached to products containing asbestos. Later, Smith testified: "It was a business decision as far as I could understand ... the corporation is in business to provide jobs for people and make money for stockholders and they had to take into consideration the effects of everything they did and if the application of a caution label identifying a product as hazardous would cut into sales, there would be serious financial implications."[95]  In 1953, National Gypsum's safety director wrote to the Indiana Division of Industrial Hygiene, recommending that acoustic plaster mixers wear respirators "because of the asbestos used in the product." Another company official noted that the letter was "full of dynamite" and urged that it be retrieved before reaching its destination. A memo in the files noted that the company "succeeded in stopping" the letter, which "will be modified."[96]
  24. 24. CTD., 1960s–1980s  Through the 1970s, asbestos was used to fireproof roofing and flooring, for heat insulation, and for a variety of other purposes. The material was used in fire-check partitioning and doors on North Sea Oil Production Platforms and Rigs.  During the mid-to late 1980s, public health concern focused on potential asbestos fiber exposures of building occupants and workers in buildings containing asbestos containing building materials (ACBM) and their risks of developing lung cancer or mesothelioma. As a consequence, the Health Effects Institute (Cambridge, MA) convened a panel to evaluate the lifetime cancer risk of general building occupants as well as service workers.[97]
  25. 25. MODERN REGULATIONS  United States  The United States remains one of the few developed countries that hasn't yet fully banned asbestos. Asbestos is still legal and widely used in such commonly used products like clothing, pipeline wraps, vinyl floor tiles, millboards, cement pipes, disk brake pads, gaskets and roof coatings.[98] In 1981, the United States Environmental Protection Agency (EPA) requested information from American companies regarding the asbestos content of their products.[99]  In 1989 the EPA issued the Asbestos Ban and Phase Out Rule which was subsequently overturned in the case of Corrosion Proof Fittings v. EPA, 947 F.2d 1201 (5th Cir. 1991). This ruling leaves many consumer products that can still legally contain trace amounts of asbestos. For a clarification of products which legally contain asbestos, read the EPA's clarification statement.[100]  In 2010, Washington State banned asbestos in automotive brakes starting in 2014.[101]  The EPA has proposed a concentration limit of seven million fibers per liter of drinking water for long fibers (lengths greater than or equal to 5 µm). The Occupational Safety and Health Administration (OSHA), has set limits of 100,000 fibers with lengths greater than or equal to 5 µm per cubic meter of workplace air for eight-hour shifts and 40-hour work weeks.[102]
  26. 26. CTD.,  OSHA regulations regarding asbestos are covered in 29 C.F.R. 1926.1101 (for construction) and 1910.1001 (for general industry). Such work is divided into four categories:  Class I asbestos work means activities involving the removal of thermal system insulation and surfacing asbestos containing materials (ACM) and presumed asbestos containing materials (PACM). Asbestos containing materials are defined by OSHA as being composed of 1% or more asbestos. Presumed asbestos containing materials are building materials that are known to have been commonly manufactured using asbestos, such as floor tiles or thermal system insulation, and were installed before 1980.  Class II asbestos work means activities involving the removal of ACM which is not thermal system insulation or surfacing material. This includes, but is not limited to, the removal of asbestos-containing wallboard, floor tile and sheeting, roofing and siding shingles, and construction mastics.  Class III asbestos work means repair and maintenance operations, where "ACM", including thermal system insulation, as well as surfacing ACM and PACM, is likely to be disturbed.  Class IV asbestos work means maintenance and custodial activities during which employees contact, but do not disturb ACM or PACM, as well as activities to clean up dust, waste and debris resulting from Class I, II, and III activities.[103]
  28. 28. HOW DO FIBRES ENTER THE LUNG?  The speed that fibers settle in air is mainly dependent on their diameter. Table 1 shows the falling speed of cylindrical fibers of different diameters.  Table 1 Falling speed of fibers in air diameter (μm) falling speed (mm/s) 100 3,000 30 250 10 30 3 2.5 1 0.3
  29. 29. CTD.,  Fibers with diameter less than 3 μm will remain suspended in the air for long enough to reach deep into the lung. Long thin fibers are just as likely to penetrate into the lungs as short thin ones.  When someone is working with asbestos some of the airborne fibers are inhaled into the lungs, which comprise a series of branching tubes. The first of these tubes is called the trachea, which is attached to the larynx. The trachea is about 2 cm in diameter and approximately 12 cm long. The trachea divides into the left and right bronchi. After a few centimeters these in turn divide into segmental bronchi and so on with about 25 further sets of branches.  Broader fibers continue to impact in the upper sections of the tracheobronchial tree falling out of the air stream onto the walls of the bronchial tubes. However, most fibers with diameter less than 3 μm regardless of length, penetrate to the alveolus. This is the part of the lung where gas exchange between the air and the blood occurs. There are over 200 million alveoli with a total surface area of more than 100 m2.  Once a fiber has deposited in the lung there is a possibility that it may cause damage to the lung tissue. This is a condition in which the lung becomes scarred as a result of prolonged inhalation of asbestos fibers. It only occurs in people exposed to relatively large amounts of asbestos, normally over many years, such as in milling, weaving, lagging or asbestos removal operations. The scarring is more properly known as fibrosis. The part of the lung that is damaged is at the far end of the smallest bronchial tubes, the place where the lung transfers oxygen to the blood stream.  As we have seen, only the finest fibers, less than 3 μm in diameter, are able to reach this part of the lung. This is why when we come to evaluate the fiber concentration in the air we count only fibers of this diameter or less.
  30. 30. CTD.,  Once a fiber has deposited in the lung there is a possibility that it may cause damage to the lung tissue. This is a condition in which the lung becomes scarred as a result of prolonged inhalation of asbestos fibers. It only occurs in people exposed to relatively large amounts of asbestos, normally over many years, such as in milling, weaving, lagging or asbestos removal operations. The scarring is more properly known as fibrosis. The part of the lung that is damaged is at the far end of the smallest bronchial tubes, the place where the lung transfers oxygen to the blood stream.  As we have seen, only the finest fibers, less than 3 μm in diameter, are able to reach this part of the lung. This is why when we come to evaluate the fiber concentration in the air we count only fibers of this diameter or less.
  31. 31. USES OF ASBESTOS  Chrysotile was by far the most abundant asbestos form in terms of production and usage (about 93 per cent). It can be found in a wide variety of products from yarn, rope and textiles to cement, insulation boards, friction materials, gaskets and thermoplastics.  Crocidoite had a similar widespread use although the tendency was to use it in mixtures with other asbestos varieties. Amosite, because of its coarser nature, tended to find greater use in asbestos board and other rigid products. All three varieties may be found in all proportions in old laggings of pipes and boilers. Crocidoite was little used after about 1970, Amosite after about 1980 and Chrystoile after about 2000  The uses of asbestos in building construction are divided into ten broad categories:
  32. 32. USES  Spray Coatings and Lagging  Insulating Board  Ropes, Yarns and Cloth  Millboard, Paper and Paper Products  Asbestos Cement Products  Bitumen Felts and Coated Metals  Flooring Materials  Textured Coatings and Paints  Mastic, Sealants, Putties and Adhesives  Reinforced Plastics
  33. 33. CTD., OTHER ITEMS  Bitumen sink pads  Water tanks  Toilet cisterns & seats  Stair nosing  Fire blankets  Brake Liners/clutch lining  Gaskets
  34. 34. IS ASBESTOS GONE YET?  Because of its association with diseases like mesothelioma and asbestosis, new uses of asbestos have been banned in the USA by the Environmental Protection Agency. In October 1991, a U.S. federal court overturned an EPA regulation that banned most uses of asbestos by 1997. Only products that were not being manufactured, imported or processed on July 1989 remain subject to the prohibition of asbestos. While exposure to asbestos has been lowered as a result of abatement programs, it has recently reared its ugly head in materials that were never thought to contain asbestos. Vermiculite mined from Zonolite Mountain in Libby, Montana was found to contain the asbestos types tremolite and actinolite as well as four other mineral types (winchite, ricterite, fero-edenite and magnesioarfvedsonite) that are not on the EPA list of asbestos minerals, but none the less have all of the properties of asbestos.
  35. 35. CTD.,  Evidence supports the belief that these "non-asbestos forms" have resulted in asbestoses and mesothelioma among mine workers in Libby Montana. In addition, friable asbestos present in asbestos mined at Libby, Montana under the name Zonolite may be a health hazards for nursery workers, installers of popped vermiculite insulation and individuals living or working in one of the millions of buildings that contain Zonolite insulation. Some industrial grade talc has also been found to contain asbestos. Cosmetic grade talc, on the other hand, appears to be asbestos free.
  36. 36. CTD.,  In answer to the question "Is asbestos gone?", no, it is not gone, nor will it ever be gone. Unlike PCBs, DDT and dioxin asbestos is part of the natural environment. The answer is not to be totally rid of it, but to maintain a working and living environment in which airborne asbestos is in a concentration low enough that it will not result in impaired health or death from diseases like asbestosis, mesothelioma, etc. When asbestos is found to be in a state in which it is non- friable and unlikely to become friable, the present trend is to leave it alone. Sometimes removal of non-friable asbestos from buildings can increase rather than decrease the chances for exposure to friable asbestos. If it is found to be friable (crumbling and powdery, or of a type that by its very nature is likely to become airborne), removal is frequently the only answer. This process must be left to asbestos abatement specialists.
  37. 37. CTD.,  Most importantly, asbestos management must also be controlled at the source. How is it entering industrial and consumer products? At one time the only pathway considered to be important in introducing asbestos to our homes and businesses was via products in which it was an intentional ingredient. Suddenly it has been found to be an incidental impurity (as in vermiculite and talc). In addition, mineral types previously thought to be unassociated with the asbestos minerals have been found to have asbestos-like properties. Testing for asbestos at the source is necessary to limit exposure to workers and the general public. It will require government, industry and the general public working together to face the new challenges of asbestos contamination.