P.A. Baron

Performance Characteristics of the Button Personal Inhalable Aerosol Sampler

The button inhalable aerosol sampler with a curved porous inlet recently was developed and evaluated as a stationary sampler in the laboratory and in the field. The present study focused on investigating its suitability for personal inhalable aerosol sampling. The button sampler was tested at two wind velocities (0.5 and 2.0 m/sec), three particle sizes (7, 29, and 70 microm) and three orientations to the wind (0, 90, and 180 degrees). The performance characteristics of the button sampler were compared with those of three other personal samplers--the IOM (Institute of Occupational Medicine), GSP, and 37-mm closed-face filter cassette. The experiments were conducted in a wind tunnel with the samplers mounted on a full-size manikin. The direction-specific sampling efficiency of the button sampler was found to be essentially independent of the wind direction and dependent on the wind velocity to a much smaller degree than that of the three other samplers. When direction-averaged, the fit of its sampling efficiency curve to the inhalability curve was found to be better than that of the 37-mm closed-face cassette, comparable with that of the GSP sampler, and less than that of the IOM sampler. The precision of the button sampler was found to be generally equal to or better than the precision of the comparison samplers. It was concluded that the button sampler can be successfully used as a personal inhalable aerosol sampler.

New aerosol sampler with low wind sensitivity and good filter collection uniformity

Abstract The overall sampling efficiency of many aerosol samplers is sensitive to wind velocity and direction. In addition, most samplers have internal losses due to gravitational settling, electrostatic interactions, and internal turbulence. A new sampling inlet has been designed to reduce these problems. The flow patterns over the new prototype sampler were visualized in a horizontal wind tunnel. Visualization of the streamlines over the new sampler and limiting-streamline quantitative analysis showed negligible turbulence effects due to the inlets geometry. The overall sampling efficiency of the prototype sampler was compared to that of a 25 mm closed-face cassette. Uranine was used as the challenge aerosol with particle physical diameters of 13.5, 20 and 30 μm. The wind velocity ranged from 100 to 300 cm s −1 . Evaluation of the data showed the new sampler to be less significantly affected by wind direction and magnitude. The particle distribution observed on the samplers filter was found to be reasonably uniform, an advantage for several types of analyses.

Evaluation of personal aerosol samplers challenged with large particles

Abstract The Simplified Test Protocol, developed in our earlier studies for testing personal inhalable aerosol samplers, was evaluated in a specially designed small open-section, close-loop wind tunnel. The sampling efficiencies of three personal inhalable aerosol samplers (IOM, GSP, and Button Aerosol Sampler) were measured with 65 μm particles, using the Simplified Test Protocol at four inlet orientations to the wind ( 0, 90, 180 , and 270°). The results were compared with the data collected from other evaluation approaches. Analysis of variance (ANOVA) has shown that there is no statistically significant difference in the samplers’ performance when they are tested in the small and large wind tunnels following the Simplified Test Protocol and in the large wind tunnel following the conventional approach (samplers on a full-size human manikin). Thus, the Simplified Test Protocol has been shown to be suitable for the performance evaluation of personal inhalable aerosol samplers. The new wind tunnel facility was also found useful for handling very large particles, which is a considerable advantage over traditional wind tunnels. Our new wind tunnel was successfully used to measure the sampling efficiencies of the IOM, GSP, and Button Aerosol Sampler when challenged with particles of up to approximately 250 μm aerodynamic diameter at wind velocities of 50 and 100 cm s −1 . The data show that the sampling efficiency of the IOM sampler depends significantly on the wind velocity and is above 100% for particles of 165 and 241 μm mass median aerodynamic diameter. This dependence is not statistically significant for the GSP and Button Aerosol Sampler, whose sampling efficiencies are similar to each other and do not change with increasing test particle size at the indicated wind velocities. Also, the sampling efficiencies of the GSP and Button Aerosol Sampler closely follow the independent data obtained by using a breathing and rotating manikin at a wind velocity of 100 cm s −1 . The new wind tunnel design is expected to enhance the ability to extend the inhalable convention beyond 100 μm .

Simplified method for testing personal inhalable aerosol samplers

Abstract The presently available protocol for evaluating the performance of personal aerosol samplers according to the inhalable convention is difficult to satisfy as it requires a large cross-section wind tunnel. The present study was initiated to simplify and reduce the cost of the test method by mounting the test samplers on a small, stationary torso instead of a full-size rotating manikin. The simplified torso consisted of a rectangular three-dimensional body (33xa0cm wide, 21xa0cm deep, 21xa0cm high). Replicates of the personal inhalable aerosol sampler under consideration were attached in the center of each vertical face of the simplified torso representing the three principal sampling orientations (facing the wind, turned 90°, and turned 180° to the wind). When the samplers were mounted on a full-size manikin, the air flow in the vicinity of the manikin was found to depend on the sampler location, symmetry of the manikin, and position of the manikin’s arms. On the simplified torso, the magnitude and direction of the air flow near the samplers were found to be comparable to that of the manikin. When subjected to nearly monodisperse aerosol flows (particle size of 70xa0 μ m, wind velocity of 50 and 200xa0cmxa0s -1 ), both methods yielded aerosol sampling efficiencies that were statistically not different at three major sampling orientations. The advantages of the simplified torso are that fewer measurements need to be made; a smaller, less expensive wind tunnel can be used for the testing; and interlaboratory variability of personal inhalable samplers’ performance may be decreased.

Length Separation of Fibers

A classifier for separating conductive fibers according to length using dielectrophoresis has been developed and tested. The classifier consisted of two concentric steel cylinders with an annular space having a width of 3.18 mm. A high-voltage alternating field applied between the cylinders caused fibers to drift to the central cylinder. In these experiments, chrysotile fibers were generated from a fluidized bed generator and collected on the central cylinder in the classifier. Fibers collected on the central cylinder were washed off from ten equal length segments and sized by transmission electron microscopy. The median lengths of classified groups of fibers ranged from 8 to 31 μm. The length distributions of these fibers had coefficients of variation ranging from 0.17 to 0.33. The quantity of classified fibers was limited by the aerosol flow rate, which in the current system was 2.13 L/min (total flow rate through the classifier was 5.35 L/min). Limitations in the classification process prevent increasi...

MEASUREMENT OF THE SAMPLING EFFICIENCY OF PERSONAL INHALABLE AEROSOL SAMPLERS USING A SIMPLIFIED PROTOCOL

Abstract Traditional protocols for the performance evaluation of personal inhalable aerosol samplers utilize full-size manikins and large cross-section wind tunnels. Thus, these sampler evaluation procedures are complex, very costly, and time consuming. In addition, it is difficult to provide an adequately uniform wind velocity and aerosol concentration over large cross-section wind tunnels. A simplified test protocol, developed in our recent studies, is evaluated in this paper. The protocol is based on a three-dimensional rectangular simplified torso that simulates the dimensions of the human chest. This arrangement allows simultaneous measurement in four discrete orientations to the wind, thus providing useful orientation-dependent sampler information and possibly reducing the number of measurements needed. Sampling efficiencies of four personal inhalable aerosol samplers (the IOM, GSP, 37-mm closed-face cassette, and the button sampler) were measured using the simplified test protocol and the traditional approach for three particle sizes (7, 29, and 70xa0 μ m) in four inlet orientations to the wind (0, 90, 180, and 270°) and two wind velocities (0.5 and 2.0xa0mxa0s -1 ). It was found that when these samplers were mounted on the simplified torso versus the full-size manikin, the sampling efficiencies responded to changes in the sampling conditions in the same way regardless of whether the samplers were mounted on the simplified torso or the full-size manikin. Also, the sampling efficiencies were found not to be statistically different when the samplers were mounted on the simplified torso versus the full-size manikin. Thus, the simplified test protocol was shown to be suitable for the performance evaluation of personal inhalable aerosol samplers.

Application of the Thoracic Sampling Definition to Fiber Measurement

As part of a consideration of the sampling method for refractory ceramic fibers, calculations were carried out at the National Institute for Occupational Safety and Health to evaluate different approaches to fiber measurement. The most common technique for estimating fibers that can reach the lungs is to use an upper diameter limit of 3 µm in the phase contrast optical microscope counting rules. Calculations were carried out to estimate the aerodynamic diameter of fibers in several lognormal size distributions likely to occur in workplaces. Using these size distributions, the use of a 3 µm fiber diameter upper limit in the counting rules was compared with results expected from a sampler designed to collect fibers according to the thoracic definition, which is based on the aerodynamic diameter of compact particles. The other limits in the optical 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 ...

AN APPROACH TO EVALUATING AND CORRECTING AERODYNAMIC PARTICLE SIZER MEASUREMENTS FOR PHANTOM PARTICLE COUNT CREATION

An aerodynamic particle sizer (APS) can be used to make real-time measurements of the aerodynamic particle size distribution over the range of 0.5 to 32 microns. This instrument is very useful in conducting health-related aerosol measurements involving aerosol generation, respirator efficiency, and particulate sampling efficiency. One of the two signal processors within the APS can create spurious or phantom particle counts that can significantly affect relative measurements and calculated mass distributions. In the APS, particle size measurement is based upon a particles transit time between two laser beams that are perpendicular to an accelerating airflow. The signal processors measure each particles transit from the time between the two pulses of scattered light that are generated as the particle passes through the two laser beams. When only a single pulse from a particle is detected, another pulse can cause the recording of a randomly sized phantom particle. The small particle processor (SPP), which measures particle transit from the times in digital increments of 4 nanoseconds, can create phantom particles; the large particle processor (LPP), which measures particle transit times in digital increments of 66.67 nanoseconds, is designed to prevent the creation of phantom particles. These two processors overlap in the range of 5.2 to 15.4 microns.(ABSTRACT TRUNCATED AT 250 WORDS)

AN INVESTIGATION OF DUST GENERATION BY FREE FALLING POWDERS

To identify the dust generation processes, aluminum oxide powder was dropped as a free falling slug in a test chamber. The effect of the slugs mass, diameter, and drop height upon the aerosol concentration and size distribution was measured with an aerodynamic particle sizer. To differentiate between aerosol generated during the free fall and at the end of the fall, the slug was dropped either onto a flat surface or into a container of water that suppressed dust generation associated with the impact at the end of the fall. Aerosol generation occurred during the slugs free fall as well as at the end of the fall. The falling solid induced an airflow that followed the falling solid to the end of the fall. This induced airflow contained the aerosol generated during the free fall. At the end of the free fall, the induced airflow, combined with air jets created on impact, dispersed the aerosol throughout the test chamber. Additional measurements were made by using neutral buoyancy helium-filled bubbles to visualize the airflow in the test chamber. The airflow and ensuing turbulence were sufficient to keep large, inspirable particles suspended throughout the test chamber for periods greater than 10 min. During experimental work, the effect of drop height, mass, and slug diameter upon aerosol generation by a single slug of powder was studied. The results indicated that the manner in which a powder is handled may be as important as material dustiness as measured by a dustiness tester. Aerosol generation can be reduced by minimizing the contact between the falling powder and the air.

Performance Evaluation of a Fiber Length Classifier

A performance evaluation was conducted on a differential mobility classifier that separates fibers according to length using dielectrophoresis. The classifier had been constructed and used for several applications in previous studies. The performance of the classifier was predicted using a two-dimensional axisymmetric model of the flow field and then calculating particle trajectories for a variety of conditions. Based on the flow calculations, several regions of the classifier were improved to reduce likelihood of turbulent losses. For a given total flow through the classifier and a maximum voltage across the electrodes, the performance of the classifier was found to depend on the ratios of the aerosol flow to the inner and the outer sheath flows. It was found that the minimum classifiable length, the minimum length distribution width, and the throughput of classified fibers can each be optimized, but not independently. Several approaches to testing the resolution of the classifier were tried. The first w...