Air Sampling Instrument Performance I (Particulate) Papers (13-18)
13. Application of the Thoracic Sampling Definition to Fiber Measurement.
P. Baron, NIOSH, Cincinnati, OH
Airborne fibers can cause several lung diseases; in principle, sampling methods should reflect this by collecting only fibers that can reach the target organ. Definitions now exist for sampling aerosols that can reach the lungs via mouth breathing, namely the thoracic fraction as developed by ACGIH. The thoracic definition is based on the aerodynamic diameter of compact particles. NIOSH is currently developing a criteria document for refractory ceramic fibers. As part of the consideration of the sampling method for these fibers, calculations were carried out to evaluate different approaches to fiber measurement. The most common current technique for estimating fibers that can reach the lungs is to use an upper diameter limit of 3 µm in the counting rules. Calculations were carried out to estimate the aerodynamic diameter of fibers from a range of likely lognormal size distributions. Using these size distributions, the use of a 3 µm diameter upper limit in the counting rules was compared to results expected from a sampler operating according to the thoracic definition. The other limits in the counting procedure, i.e., counting only fibers longer than 5 µm and thicker than 0.25 µm, were included in the calculations. The calculations indicate that the 3 µm counting rules agrees with the thoracic definition within about ±25 for a wide range of possible size distributions. The advantages of using a thoracic sampler would be to reduce analyst decision making (all fibers collected would be counted) and to reduce the non-thoracic dust on the sample, making the sample easier to count. Until the thoracic samplers are available for fibrous aerosols, incorporating the 3 µm upper diameter limit in the fiber counting rules may serve as a surrogate for thoracic sampling.
14. Development of the New Federal Reference Method for Fine Particles.
R. Wiener, U.S. Environmental Protection Agency, Research Triangle Park, NC
A key element in considering a revised standard will be sampling for fine particles in addition to current PM10 requirements. This will result in the need for a new federal reference method (FRM) for fine particles. Goals for the FRM for fine particles include: 24-hour measuring period; automated sequential sampling, without daily maintenance; easy to use; capability of providing sample for later chemical analysis; ability to operate under wide range of ambient conditions (temperature and pressure); comparability to existing manual measurements and historical epidemiological data base; a sharp cut; appropriate quality assurance requirements for reference and equivalent methods; and sample collection at ambient temperatures. This is to be accomplished by providing for three classifications of samplers. First, the Reference Method, a low volume, single-day, sampler based on filtration and gravimetric determination of mass and specified primarily by design. Second, (Class 1 Equivalent) equivalent methods very similar to the reference method, including sequential (multi-day) samplers based on minor modifications of the reference method sampler. Third, to permit technological flexibility, provisions will be made for an instrument (Class II Equivalent) significantly different from the reference sampler.
Designation of a particle sampler as a Federal Reference Method (FRM) will be based on a demonstration that a vendor's instrument meets the design specifications, performance requirements, and quality control standards to be specified in the regulation. Designation of a Class I Equivalent sampler will require the same tests as the FRM, with provisions to demonstrate that any alteration of component parts or inclusion of additional parts to those specified for the FRM does not alter the performance of the sampler. The Class II Equivalent samplers may use components and methods other than those specified in the FRM (e.g., continuous analyzers based on measurement principals different from the reference method, a different inlet, size separator, or filtration collection methodology). The samplers would require full equivalency testing and meet quality assurance and control requirements. Equivalency testing will include a combination of laboratory and field test to demonstrate the ability of the proposed method to provide results similar to the Reference Method in accuracy and precision.
15. Strategy and Timetable for the Adoption of the CEN/ISO Sampling Conventions in the U.K.
L. Kenny, Health and Safety Laboratory, Sheffield United Kingdom; S. Bristow, T. Ogden, Health and Safety Executives, London, England
The implementation of the CEN/ISO sampling conventions requires decisions on which sampling methods to recommend, estimation of the likely impact that changing sampling methods could have on apparent exposures, and adjustment where necessary of exposure limit values. Changes will be necessary both to the UK's official guidance and regulation. This paper outlines the strategy that HSE intends to pursue, and the time scale needed for practical adoption of the CEN/ISO conventions in the UK.
At present, the UK has no exposure limits for thoracic dust and we need only consider the conventions for respirable and inhalable dusts. The current UK method for respirable dust, the Higgins-Dowell cyclone, agrees best with the CEN/ISO respirable convention when operated at a flow rate of 2.2 lpm. The effect of changing from the current flow rate of 1.9 lpm will be to decrease apparent dust concentrations by about 20% on average. Thus, in order to retain the same standards of control in the workplace, the exposure limits should also be decreased by 20%. For the majority of substances, UK exposure limits have the status of guidance, and can be changed after public consultation with the agreement of the Health and Safety Commission. Two substances_crystalline and barium sulphate_have respirable dust limits incorporated into regulation, changes to which require approval of Parliament. The exposure limit for silica is under review at present.
Evaluation of the current UK method for "total inhalable" dust, the seven-hole sampler, shows that in low external wind speeds it follows the inhalable convention adequately (although other samplers perform better). We consider therefore that UK exposure limits for "total inhalable" dust can be converted into "inhalable" limits without any numerical change. This greatly simplifies the formal adoption of the CEN/ISO inhalable convention.
Publication of new guidance on dust sampling will enable HSE to recommend a wider range of samplers, to include all instruments having satisfactory performance with respect to the new conventions. Revised guidance will be issued in January 1997, and will coincide with the publication of the new respirable dust exposure limits, subject to all the necessary agreements and consultations.
16. Outcome of a Collaborative European Study of Personal Inhalable Aerosol Sampler Performance.
L. Kenny, Health and Safety Laboratory, Sheffield, United Kingdom; R. Aitken, Institute of Occupational Medicine, Edinburgh, United Kingdom
Following the worldwide agreement of sampling conventions for inhalable, thoracic, and respirable aerosol fractions, a working group of Committee European de Normalisation (CEN) developed a pre-standard for the performance of instruments used for workplace aerosol sampling. In order to test the general applicability of this sampler performance standard, this study was set up to examine the experimental, statistical, and mathematical procedures it recommended. This aim was achieved by working through the recommended test protocols with eight types of personal inhalable aerosol sampler used for workplace monitoring in Europe and elsewhere.
The samplers were evaluated in terms of bias and precision with respect to the inhalable convention. All the samplers were found to perform best in low external wind speeds, which of the range of conditions tested are thought to be closest to those normally found in indoor workplaces. At low wind speeds, five of the eight sampler types tested gave adequate agreement with the inhalable convention, and the remaining three gave adequate agreement after the application of correction factors. At moderate wind speeds, only two out of the eight samplers gave adequate agreement without correction. At high external wind speeds, none of the tested samplers performed well. In addition to bias, there were significant differences in the ease of use and handling of the different samplers, reflected in the precision of the results at all wind speeds.
The results of the project have led to recommendations for revising the CEN pre-standard, in order to simplify the test protocols and lower their cost, in particular by reducing the number of compulsory tests and concentrating on low wind speed conditions. However, some further work will be needed to develop suitable test facilities and methods. The sampler performance data obtained in this study were affected by large experimental errors, but will nevertheless contribute to decisions on how to implement the inhalable sampling convention in industrial hygiene practice.
17. Field Testing of New Multidirectional Sampling Inlet for Airborne Particulates: Simultaneous Measurement of Total Dust, Fungal Spores and Lead.
B. Hauck, G. Mainelis, T. Reponen, A. Reponen, University of Cincinnati, Cincinnati, OH
A new personal sampling inlet with low wind sensitivity and good filter collection uniformity has recently been developed and evaluated by the investigators. The inlet design includes a circular base fitted with a spherical screen with numerous evenly spaced pores, thus giving the sampler a multidirectional sampling capability. In this study the new sampler prototype (178 µm pore size, 9% porosity) has been evaluated in the field as an area sampler in houses where environmental cleanups have been conducted. Teams of cleanup workers, made up of 4-5 members, used HEPA vacuum cleaners to purge the dwellings of surface contamination. All floor areas, including under and behind all furniture, were vacuumed three times and all surfaces wiped with sanitizing solution also three times. The cleaning teams, while working in poorly maintained inner city houses, were at risk for exposure to high levels of total dust, fungal spores, and lead. To assess the exposures, five homes were evaluated involving a wide range of cleanliness levels. Samples of airborne total dust, fungal spores, and lead were collected on 0.8 µm pore size, 25 and 37 mm diameter PVC filters during cleanup. Two different sample inlets were utilized: the conventional 37-mm diameter three-piece cassette and the new multidirectional 25-mm diameter sampling inlet. Four co-located samplers of each type were tested. The samples were collected at air flow rates of 2 or 10 lpm using both stationary and battery-operated pumps. The sample filters were analyzed for total dust using gravimetric analysis and then for fungal spores and lead. The fungal spore concentration was determined using Acridine Orange Staining and Epifluorescence Microscopy, and lead level was measured by Atomic Absorption Spectroscopy. The results of this ongoing study indicate that workers are not exposed to hazardous levels of total dust, fungal spores, and lead during these 4-5 hour cleanup operations. Comparison of the new with the conventional aerosol sampling inlet demonstrates lower standard deviation of measured concentrations and better spatial distribution of particulates on the filter when using the new inlet.
18. Quantification Evaluation of Real Time Beryllium Air Monitoring Using Laser-Induced Breakdown Spectroscopy.
N. Vahdat, Tuskegee University, Tuskegee, AL; M. Hoover, Inhalation Toxicology Research Institute, Albuquerque, NM; J. Johnson, G. Coutts, Lawrence Livermore National Laboratory, Livermore, CA
Beryllium particles in air can represent a significant inhalation health hazard. The traditional methods of monitoring beryllium particles in air involve passing a known volume of air through a filter, chemically dissolving the collected material and determining the beryllium concentration of the solution using flame atomization atomic absorption spectrometry or inductively coupled plasma analysis. The process is time consuming requiring 6 to 8 hours. In this paper we discuss the use of laser-induced breakdown spectroscopy (LIBS) for real-time beryllium air monitoring. A small transportable Beryllium Air Monitor System based on the LIBS technique was developed at the optics for focusing the output of the laser, and systems for air sampling, emission detection, and instrument control. Beryllium particles in the air sample entering the ionization chamber of the instrument are vaporized and ionized. Light emitted from the plasma is used to identify and quantify the airborne beryllium concentrations. The instrument was tested in a series of calibration experiments and data were collected for several beryllium particle size ranges and concentrations in the air. If a particle is completely vaporized by the spark, one would expect the signal received from the LIBS instrument to be proportional to the mass of the particle. There is, however, evidence that large particles are not completely vaporized, preventing use of linear relationships between mass and signal. Based on the experimental data, a theoretical model involving surface and volume of particles was developed which can be used to quantify the airborne beryllium concentrations.
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