Asbestos Abatement >> Asbestos Removal Techniques

In accordance with these concepts, it has been suggested that amphibole asbestos is more toxic than chrysotile asbestos, mainly because physical differences allow chrysotile to break down and clear from the lung, whereas amphibole is not removed and Asbestos Removal Techniques builds up to high levels in lung tissue (Churg 1993). 

Some researchers believe the resulting increased duration of exposure to amphibole asbestos significantly increases the risk of mesothelioma and, to a lesser extent, asbestosis and lung cancer (Churg 1993). OSHA continues, however, to regulate chrysotile and amphibole asbestos as one substance, Asbestos Removal Techniques as both types increase the risk of disease (OSHA 1994). 

EPA’s Integrated Risk Information System (IRIS) assessment of asbestos also treats mineralogy (and fiber length) as equipotent (EPA 2002a). Evidence suggesting that the different types of asbestos fibers vary in carcinogenic potency and Asbestos Removal Techniques site specificity is to some degree limited by the lack of epidemiological information on exposure to pure mineral types. 

Other data indicate that differences in fiber size distribution and Asbestos Removal Techniques other process differences can contribute at least as much as fiber type to the observed variation in risk (Berman and Crump 1999a, 1999b). Counting fibers using the regulatory definitions (see below) does not adequately describe risk of health effects. 

Fiber size, shape, and composition contribute collectively to risk in ways that are still being elucidated. For example, shorter fibers appear to deposit preferentially in the deep lung, Asbestos Removal Techniques but longer fibers may disproportionately increase the risk of mesothelioma (ATSDR 2001; Berman and Crump 1999a, 1999b). 

Some of the unregulated amphibole minerals, such as the winchite present in Libby asbestos, can exhibit asbestiform characteristics and contribute to risk. Fiber diameters greater than 2 µm–5 µm are considered above the upper limit of respirability (i.e., too large to inhale), and Asbestos Removal Techniques thus do not contribute significantly to risk. 

Methods to assess the risks posed by varying types of asbestos are being developed and are currently awaiting peer review (Berman and Crump 1999a,1999b). Current Standards, Regulations, and Asbestos Removal Techniques Recommendations for Asbestos In industrial applications, an asbestos-containing material (ACM) is defined as any material with >1% bulk concentration of asbestos (EPA 1989). 

It is important to note that 1% is not a healthbased level, Asbestos Removal Techniques but instead represents the practical detection limit in the 1970s when EPA regulations were created. Studies have shown that disturbing soil containing <1% amphibole asbestos can, however, suspend fibers at levels of health concern (Weis 2001). 

Friable asbestos (asbestos which is crumbly and Asbestos Removal Techniques can be broken down to suspendible fibers) is listed as a hazardous air pollutant on EPA’s Toxic Release Inventory (EPA 2002b). This classification requires companies that release friable asbestos at concentrations >0.1% to report the release under Section 313 of the Emergency Planning and Community Right-to-Know Act. 

OSHA’s permissible exposure limit (PEL) is 0.1 f/cc for asbestos fibers with lengths >5 µm and with an aspect ratio (length: width) >3:1, as determined by PCM (OSHA 1994). This Asbestos Removal Techniques value represents a time-weighted average (TWA) exposure level based on 8 hours per day for a 40­ hour work week. 

In addition, OSHA has defined an "excursion limit,” which stipulates that no worker should be exposed in excess of 1 f/cc as averaged over a sampling period of 30 minutes (OSHA 1994). Historically, Asbestos Removal Techniques the OSHA PEL has steadily decreased from an initial standard of 12 f/cc established in 1971. 

The PEL levels prior to 1983 were determined on the basis of empirical worker health observations, Asbestos Removal Techniques while the levels set from 1983 forward employed some form of quantitative risk assessment. ATSDR has used the current OSHA PEL of 0.1 f/cc as a reference point for evaluating asbestos inhalation exposure for past workers. 

ATSDR does not, however, support using the PEL for evaluating exposure for community members, Asbestos Removal Techniques because the PEL is based on an unacceptable health risk level for this population. 

In response to the World Trade Center disaster in 2001 and Asbestos Removal Techniques an immediate concern about asbestos levels in buildings in the area, the Department of Health and Human Services, EPA, and the Department of Labor formed the Environmental Assessment Working Group. 

This Asbestos Removal Techniques work group was made up of ATSDR, EPA, CDC’s National Center for Environmental Health, the National Institute of Occupational Safety and Health (NIOSH), the New York City Department of Health and Mental Hygiene, the New York State Department of Health, and OSHA. The work group set a short-term reoccupation level of 0.01 f/cc (ATSDR 2003). 

In 2002, a multiagency task force headed by EPA was formed specifically to evaluate indoor environments for the presence of contaminants that might pose long-term health risks to residents in Lower Manhattan. The task force, Asbestos Removal Techniques which included staff from ATSDR, developed a health-based benchmark of 0.0009 f/cc for indoor air. 

This benchmark was developed to be protective under long-term exposure scenarios, and is predicated on risk-based criteria that include conservative exposure assumptions and Asbestos Removal Techniques the current EPA cancer slope factor. The 0.0009 f/cc benchmark for indoor air was formulated on the basis of chrysotile fibers and is therefore most appropriately applied to airborne chrysotile fibers (EPA 2003). 

NIOSH set a recommended exposure limit of 0.1 f/cc for asbestos fibers longer than 5 µm. This Asbestos Removal Techniques limit is a TWA for up to a 10-hour workday in a 40-hour work week (NIOSH 2002). The American Conference of Government Industrial Hygienists has also adopted a TWA of 0.1 f/cc as its threshold limit value (ACGIH 2000). 

EPA has set a maximum contaminant level (MCL) for asbestos fibers in water of 7,000,000 fibers longer than 10 µm per liter, based on an increased risk of developing benign intestinal polyps (EPA 2002c). Many states use the same value as a human health water quality standard for surface water and Asbestos Removal Techniques groundwater. Asbestos is a known human carcinogen. 

Historically, EPA has calculated an inhalation unit risk for cancer (cancer slope factor) of 0.23 per f/cc of asbestos (EPA 2002a). This value estimates additive risk of lung cancer and mesothelioma using a relative risk model for lung cancer and Asbestos Removal Techniques an absolute risk model for mesothelioma. This quantitative risk model has significant limitations. 

First, Asbestos Removal Techniques the unit risks were based on measurements with phase contrast microscopy and therefore cannot be applied directly to measurements made with other analytical techniques. Second, the unit risk should not be used if the air concentration exceeds 0.04 f/cc—the slope factor above this concentration might differ from that stated (EPA 2002a). 

Perhaps the most significant limitation is that the model does not consider mineralogy, fiber-size distribution, or other physical aspects of asbestos toxicity. Given the limitations of the method currently used and the knowledge gained since it was implemented in 1986, Asbestos Removal Techniques EPA is in the process of updating its asbestos quantitative risk methodology.

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