Asbestiform Fibers Nonoccupational Health Risks (1984) / Chapter Skim
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4 Measurement of Exposure to Asbestiform Fibers
4 Measurement of Exposure to Asbestiform Fibers
Pages 82-96
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From page 82... ...
In the gross mass methods, airborne dust wan collected by filtration, precipitation, or impaction, and the total dust was determined by simple weighing on conventional balances. X-ray diffraction techniques were used to identify mineral phases present in the dust; magnesium analysis was used as an index of chrysotile asbestos 82
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From page 83... ...
Mass, grose Filtcr Gravimetric Electrostat ic Gravime t ric prec ipitator ~ piezoe lec tric Mass, respirable Count Impingement Mineral ident if icae ion by x-ray; chrysot i le ident if icat ion by magnesium analysis Not appl icable Impac t ion Hi-vol/filter Beta-absorpt ion Mic roscop ic Horizontal e lu- Gravime t ric triator/f ilter Cycloneffilter Gravimetr~ Light micro~cope Not app 1 icab le Mineral ident i f icat ion by x-ray Mineral ident i f icat ion by x-ray; chrysot i le ident if icae ion by magne ~ ium ana ly ~ i s Mineral identification by x-ray; chry~ot i le itent if icat ion by magnesium analys is Identification by morphology Impac t ion Light mic rose ope Ident i f icat i on by morpho logy The rma 1 Light mic rose ope Ident i f icat ion prec ipitator by morphology Hembrane filter Light microscope Identification by phase contrast morphology; mineral 't ident i f ic at ion by · dispersion staining ~. Nuclepore filter TEM,b SEM,C .Hineral identification image recog- by SAED;d chemical nit ion composition by - EDXAe Nuc lepore f i 1 te r Light sca t t e ring Ident i f icat i on o f fibers by magnetic alignasnt aAdapted from Burdett et al., 1980.
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From page 84... ...
In occupational environments, the units commonly used are milligrams of dust per cubic meter of air, whereas the much lower dust masses found in nonoccupational ambient environments are more conveniently expressed as nanograms of dust per cubic meter of air. Counting methods are far more sensitive than mass determinations, since samples with too little mass to be weighed are usually adequate for counting.]
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From page 85... ...
A portion of the filter may be rendered transparent and then examined with a phase contrast light microscope. Fibers with an aspect ratio greater than 3 to 1 are counted on a prescribed, representative area of the filters (National Inst itute for Occupational Safety and Health, 1977~.
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From page 86... ...
. MEASURING ASBESTOS DUST IN THE AMBIENT ENVIRONMENT The number of fibers >5 Am in length counted on membrane filters by phase contrast light microscopy is used as an index for exposure in the industrial workplace.
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From page 87... ...
For example, with the phase contrast light microscope, fibers longer than 5 Am are counted as a single species, whereas shorter fibers are not counted at al 1. Therefore, a given fiber count obtained by this technique would undoubtedly represent very different numbers of fibers and mass concentrations than the same fiber count obtained by electron microscopy.
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From page 88... ...
aRatios developed by Cook and Ilarklund, 1982; Davis et al., 1978; Dement et al., 1982; Lynch et al., 1970; Rohl et al., 1976, and the British Occupational Hygiene Soc iety (Walton, 1982) were used to construct the table.
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From page 90... ...
For example, in studies reported by Thompson (1978) , 20 specimens obtained downwind from an emission source had average asbestos fiber mass concentrations ranging from 0.03 to 8,200 ng/m3.
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From page 91... ...
However, because remote ambient environments, by definition, are distant from known asbestos sources, the identity of fibers there can neither be assumed a priori nor easily determined with any certainty, especially by light microscopy (Langer, 1979~. The light microscope specified for analysis of membrane filter specimens (phase contrast microscopy)
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From page 92... ...
Current methods for determining ambient concentrations of f ibrous particles could benefit from substantial improvement. However, sufficient standardization is needed to allow comparisons of data from various laboratories 80 that a data bank of ambient concentrat ions can be established for use by epidemiologists and other researchers.
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From page 93... ...
Direct transfer techniques and TEM examinat ion of the preparer ions, or other techniques that allow examination of particles as they existed in the aerosol, should be used. Fiber monitoring techniques for use in nonoccupational environments should be standardized so that results from various studies are comparable.
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From page 94... ...
Inhaled Particles and Vapours, Pergamon Press, Oxford. British Occupational Hygiene Society Committee on Asbestos.
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From page 95... ...
1979. USPHS/NIOSH membrane filter method for evaluating airborne asbestos fibers.
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From page 96... ...
1982. me nature, hazards and asseasment of occupational exposure to airborne asbestos dust: A review.
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