Asbestos airborne, sampling

Indirect methods Indirect methods are used where there is an excessive amount of organic fiber along with the asbestos, or some other soluble mineral fiber in an airborne sample. In these cases, treatment of the sample in a low-temperature oxygen plasma incinerator, or dissolution of the sample in a suitable solvent, followed by redeposition of the cleaned sample on a second filter can make the analysis... 

Area (or ambient) air sampling is conducted to get an estimate of the numbers of airborne asbestos fibers present in a building. It is used as an assessment tool in evaluating the potential hazard posed by asbestos to aU building occupants. 

In still another case, airborne asbestos is frequently qualitatively identified and/or sampled by either a licenced engineer or a certified asbestos contractors, and quantitatively analyzed by a certified laboratory. The building material, such as the insulation for the plumbing system, however, can only be removed by a State-certified asbestos contractor. The readers are referred to Section 3.6.3 for air sampling and identification of asbestos-containing materials. 

In 1956 McCrone founded McCrone Associates, a private analytical laboratory in which the principal analytical technique employed was polarized light spectroscopy. Over the years he and his staff learned to visually identify over 30000 particles (McLafferty 1990). McCrone Associates speciahzed in the identification of polymorphs, asbestos samples, airborne impurities, among others. McCrone recently endowed a chair of chemical microscopy to Cornell University, his Alma Mater. 

Light Microscopic Method. Phase contrast microscopy (PCM) accurately assesses fiber exposure levels for fibers 5 pm in length and >0.25 pm in diameter. Furthermore, PCM cannot differentiate between asbestos and nonasbestos fibers. Currently, the standard method for the determination of airborne asbestos particles in the workplace is NIOSH Method 7400, Asbestos by Phase Contrast Microscopy (NIOSH 1994a). OSHA considers that sampling and analytical procedures contained in OSHA Method ID-160 and NIOSH Method 7400 are essential for obtaining adequate employee exposure monitoring. Therefore, all employers who are required to conduct monitoring are required to use these or equivalent methods to collect and analyze samples (OSHA 1994). In NIOSH Method 7400, asbestos is collected on a 25 mm cellulose ester filter (cassette-equipped with a 50 mm electrically-conductive cowl). The filter is treated to make it... 

Sheehan MJ, Reynolds JW. 1992. Airborne asbestos analysis of low fiber density samples A comparison of the A and B counting rules of the NIOSH method 7400. Applied Occupational Environmental Hygiene 7(1) 38-41. 

Verma DK, Clark NE. 1995. Relationships between phase contrast microscopy and transmission electron microscopy results of samples from occupational exposure to airborne chrysotile asbestos. Am Ind Hyg Assoc J 56 866-873. 

X-ray methods in analyzing air and/or bulk material samples offers the most accurate approach to estimating airborne asbestos concentrations. 

Increased incidences of pleural tumors resembling human mesotheliomas have been observed in rats (Stanton et al. 1981 Wagner et al. 1982) and hamsters (Smith et al. 1979) exposed to tremolite asbestos by intrapleural implantation, in rats exposed to tremolite asbestos or actinolite asbestos samples by intraperitoneal injection (Davis et al. 1991 Pott et al. 1989 Roller et al. 1996, 1997), and in rats exposed to airborne tremolite asbestos (Davis et al. 1985a). Increases in most of these studies were statistically significant. 

As found in 29 CFR 1910.1001, the OSHA PEL for asbestos fibers (i.e., actinolite asbestos, amosite, anthophyllite asbestos, chrysotile, crocidolite, and tremolite asbestos) is an 8-hour TWA airborne concentration of 0.1 fiber (longer than 5 micrometers and having a length to diameter ratio of at least 3 to 1) per cubic centimeter of air (0.1 fiber/cm ), as determined by the membrane filter method at approximately 400X magnification with phase contrast illumination. No worker should be exposed in excess of 1 fiber/cm (excursion limit) as averaged over a sampling period of 30 minutes. 

According to 29 CFR 1926.1101, employers must ensure that no employee is exposed to an airborne concentration of asbestos in excess of the PEL (0.1 fiber per cubic centimeter of air as an 8-hour time-weighted average (TWA)). Employers must also ensure that no employee is exposed to an airborne concentration of asbestos in excess of the STEL (1.0 f/cc as averaged over a sampling period of 30 minutes). 

Cover the general requirements for monitoring to determine asbestos exposure levels. Each employer who has a work operation where exposure monitoring is reqiiired must perform monitoring to determine the airborne concentrations of asbestos to which employees could be exposed. Determinations of employee exposure have to be made from breathing zone air samples that are representative of the 8-hour TWA and 30-minute short-term exposures of each employee. 

The Code of Practice lays down the tests to be carried out which include, for both Parts I and II, checks of pressures, velocities at various points and pressure differences across fans and filters. Part I tests should also include for sampling and dust lamp tests to check that the airborne asbestos is being controlled. Part II tests should, additionally, include a qualitative check using the dust lamp (Figure 29.2). 

EH10 Asbestos - Exposure limits and measurements of airborne dust concentrations (1988) EH 25 Cotton dust sampling (1980)... 

All individuals performing asbestos analysis must have taken the NIOSH course for sampling and evaluating airborne asbestos dust or an equivalent course. 

Calculate the estimated airborne asbestos fiber concentration on the filter sample using the following formula ... 

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