Asbestos sampling methods

For determinations of asbestos fibers in the liquid samples methods that involve filtering the liquids through a polycarbonate or cellulosic filter of 0.2 pm pore size were used. 

NIOSH method 7400 for mounting sampling cassette filters on microscope slides used primarily for asbestos sampling work. National Institute for Occupational Safety and Heafth, 1986. Preview free Purchase 80... 

The Occupational Safety and Health Administration (OSHA) standard for exposure to asbestos defines a fiber as one at least 5 p,m long with a length/diameter ratio of at least 3.0. The TLV-TWA is 0.1 fibers/cc of air the excursion limit for a 30-min sampling period is 1.0. The standard, published in 29 CFR 1910.1001 specifies sampling methods and fiequencies as well as the analytical procedure (NIOSH Method 7400). Some countries allow higher concentrations of fiber. In Brazil, Canada, and Mexico, for example, the TLV is 2 fibers/ml. In the European Union, the TLV is 0.6 fibers/ml (0.25 in Germany), with an action level of 0.2. 

Standard deviations from two to five or more. This means that the upper seventeenth percentile may be as much as from two to five times the mean. This variabihty is compounded by the problem of estimating the exposure of a group of workers having differing exposures to find the most exposed workers. Compared to this environmental variabihty, the variabihty introduced by the sampling and analytical error is smah, even for those methods such as asbestos counting, which are relatively imprecise. 

The contrast for specimen detail in the field of view is gready enhanced by darkfield illumination (10). The degree of contrast and sensitivity of detection of smaH-object details depend on the relative indices of the specimen and the mounting Hquid and on the intensity of the illumination. Darkfield illumination is not, however, a satisfactory solution for biologists who need direct transmitted light in order to observe specimens, especially stained specimens. It is, however, very usefiil in detecting asbestos fibrils that often exist in door tiles or water and air samples as 20-nm fibers (10 times finer than the resolution of an asbestos analyst s usual microscope) (11). Darkfield illumination yields an uimatural appearance and difficulties in interpretation hence, a need for better contrast methods stiU exists. 

Instrumental Methods for Bulk Samples. With bulk fiber samples, or samples of materials containing significant amounts of asbestos fibers, a number of other instmmental analytical methods can be used for the identification of asbestos fibers. In principle, any instmmental method that enables the elemental characterization of minerals can be used to identify a particular type of asbestos fiber. Among such methods, x-ray fluorescence (xrf) and x-ray photo-electron spectroscopy (xps) offer convenient identification methods, usually from the ratio of the various metal cations to the siUcon content. The x-ray diffraction technique (xrd) also offers a powerfiil means of identifying the various types of asbestos fibers, as well as the nature of other minerals associated with the fibers (9). 

Figure 6.13. Experimental arrangement of the hot-explosive compaction method for the preparation of consolidated Ni-Al alloys (after Kecskes etal. 2004). (a) Precursor powder sample inside a steel-tube container placed in, (b) an asbestos thermal insulation sheet (c) a concentric card-box filled with the powdered explosive (80% NH4NO3 + 20% TNT) (d) threaded steel plugs serving as contacts for the preliminary heating and to be lifted off just before detonating the explosive (e) detonating cords.

The bomb method for sulfur determination (ASTM D129) uses sample combustion in oxygen and conversion of the sulfur to barium sulfate, which is determined by mass. This method is suitable for samples containing 0.1 to 5.0% w/w sulfur and can be used for most low-volatility petroleum products. Elements that produce residues insoluble in hydrochloric acid interfere with this method this includes aluminum, calcium, iron, lead, and silicon, plus minerals such as asbestos, mica, and silica, and an alternative method (ASTM D1552) is preferred. This method describes three procedures the sample is first pyrolyzed in either an induction furnace or a resistance furnace the sulfur is then converted to sulfur dioxide, and the sulfur dioxide is either titrated with potassium iodate-starch reagent or is analyzed by infrared spectroscopy. This method is generally suitable for samples containing from 0.06 to 8.0% w/w sulfur that distill at temperatures above 177°C (351°F). 

A method to measure soluble organic carbon in seawater includes oxidation of the organic materials to C02 with K2S2Og, followed by gravimetric determination of the C02 trapped by a column of NaOH-coated asbestos. A water sample weighing 6.234 g produced 2.378 mg of CO, (FM 44.010). Calculate the ppm carbon in the seawater. 

Air drawn through a 0.8 to 1.2 mm cellulose ester membrane filter, asbestos fibers counted by positive phase contrast microscopy technique sample prepared by acetone/triacetin method (NIOSH Method 7400, 1985). 

Alternatively, asbestos fibers collected on the filter counted by TEM, following the modified Jaffe wick technique for sample preparation (NIOSH Method 7402, 1987). 

Percent chrysotile asbestos in bulk samples may be measured by X-ray powder diffraction (NIOSH Method 9000, 1984) sample dust grinded under liquid N2 wet sieved through 10-mm sieve sieved material treated with 2-propanol agitated in an ultrasonic bath filtered on a silver filter measured by XRD, using a Cu target X-ray tube. 

The purpose of this chapter is to describe the analytical methods that are available for detecting, measuring, and/or monitoring asbestos, its metabolites, and other biomarkers of exposure and effect to asbestos. The intent is not to provide an exhaustive list of analytical methods. Rather, the intention is to identify well-established methods that are used as the standard methods of analysis. Many of the analytical methods used for environmental samples are the methods approved by federal agencies and organizations such as ERA and the National Institute for Occupational Safety and Health (NIOSH). Other methods presented in this chapter are those that are approved by groups such as the Association of Official Analytical Chemists (AOAC) and the American Public Health Association (APHA). Additionally, analytical methods are included that modify previously used methods to obtain lower detection limits and/or to improve accuracy and precision. 

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... 

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