Darrah K. Sleeth

Performance Study of Personal Inhalable Aerosol Samplers at Ultra-Low Wind Speeds

The assessment of personal inhalable aerosol samplers in a controlled laboratory setting has not previously been carried out at the ultra-low wind speed conditions that represent most modern workplaces. There is currently some concern about whether the existing inhalable aerosol convention is appropriate at these low wind speeds and an alternative has been suggested. It was therefore important to assess the performance of the most common personal samplers used to collect the inhalable aerosol fraction, especially those that were designed to match the original curve. The experimental set-up involved use of a hybrid ultra-low speed wind tunnel/calm air chamber and a rotating, heating breathing mannequin to measure the inhalable fraction of aerosol exposure. The samplers that were tested included the Institute of Occupational Medicine (IOM), Button, and GSP inhalable samplers as well as the closed-face cassette sampler that has been (and still is) widely used by occupational hygienists in many countries. The results showed that, down to ∼0.2 m s(-1), the samplers matched the current inhalability criterion relatively well but were significantly greater than this at the lowest wind speed tested. Overall, there was a significant effect of wind speed on sampling efficiency, with lower wind speeds clearly associated with an increase in sampling efficiency.

Characterization of indoor air contaminants in a randomly selected set of commercial nail salons in Salt Lake County, Utah, USA

Air samples were collected in 12 randomly selected commercial nail salons in Salt Lake County, Utah. Measurements of salon physical/chemical parameters (room volume, CO2 levels) were obtained. Volatile organic compound (VOC) concentrations were collected using summa air canisters and sorbent media tubes for an 8-h period. Multivariate analyses were used to identify relationships between salon physical/chemical characteristics and the VOCs found in the air samples. The ACGIH® additive mixing formula was also applied to determine if there were potential overexposures to the combined airborne concentrations of chemicals monitored. Methyl methacrylate was detected in 58% of the establishments despite having been banned for use in nail products by the state of Utah. Formaldehyde was found above the NIOSH REL® (0.016 ppm) in 58% of the establishments. Given the assortment of VOCs to which nail salon workers are potentially exposed, a combination of engineering as well as personal protective equipment is recommended.

Inhalability for aerosols at ultra-low windspeeds

Most previous experimental studies of aerosol inhalability were conducted in wind tunnels for windspeeds greater than 0.5 ms-1. While that body of work was used to establish a convention for the inhalable fraction, results from studies in calm air chambers (for essentially zero windspeed) are being discussed as the basis of a modified criterion. However, information is lacking for windspeeds in the intermediate range, which - it so happens - pertain to most actual workplaces. With this in mind, we have developed a new experimental system to assess inhalability - and, ultimately, personal sampler performance - for aerosols with particle aerodynamic diameter within the range from about 9 to 90 μm for ultra-low windspeed environments from about 0.1 to 0.5 ms1. This new system contains an aerosol test facility, fully described elsewhere, that combines the physical attributes and performance characteristics of moving air wind tunnels and calm air chambers, both of which have featured individually in previous research. It also contains a specially-designed breathing, heated, life-sized mannequin that allows for accurate recovery of test particulate material that has been inhaled. Procedures have been developed that employ test aerosols of well-defined particle size distribution generated mechanically from narrowly-graded powders of fused alumina. Using this new system, we have conducted an extensive set of new experiments to measure the inhalability of a human subject (as represented by the mannequin), aimed at filling the current knowledge gap for conditions that are more realistic than those embodied in most previous research. These data reveal that inhalability throughout the range of interest is significantly different based on windspeed, indicating a rise in aspiration efficiency as windspeed decreases. Breathing flowrate and mode of breathing (i.e. nose versus mouth breathing) did not show significant differences for the inhalability of aerosols. On the whole however, the data obtained here are within the range of inhalability data that exist from the large body of the previous experimental work performed at the higher windspeeds. These latest findings are an important contribution to the ongoing discussion in international standards-setting bodies about the possible adjustment of the quantitative definition of what constitutes the inhalable fraction.

Proposed Modification to the Inhalable Aerosol Convention Applicable to Realistic Workplace Wind Speeds

The current convention for sampling inhalable aerosols was based on several mannequin studies performed in wind tunnels at wind speeds between 0.5 and 4 m s(-1). In reality, as we now know, the wind speed in most modern indoor working environments is generally at or below ∼0.2 m s(-1). Inhalability studies performed in calm air aerosol chambers have shown that human aspiration efficiency at essentially zero wind speed is not consistent with the existing inhalable aerosol convention, calling into question the universal applicability of the current standard. More recently, experiments were carried out in a new hybrid wind tunnel-calm air chamber at more representative workplace wind speeds, between ∼0.1 and 0.5 m s(-1), to fill in this knowledge gap. Comparing these new data to both the existing inhalable aerosol convention and a recently proposed alternative for low wind movement suggests that, while the existing inhalable aerosol convention remains appropriate for wind speeds above ∼0.2 m s(-1), the modified version is more appropriate for the range below ∼0.2 m s(-1).

A Simple and Disposable Sampler for Inhalable Aerosol

The state-of-the-art for personal sampling for inhalable aerosol hazards is constrained by issues of sampler cost and complexity; these issues have limited the adoption and use of some samplers by practicing hygienists. Thus, despite the known health effects of inhalable aerosol hazards, personal exposures are routinely assessed for only a small fraction of the at-risk workforce. To address the limitations of current technologies for inhalable aerosol sampling, a disposable inhalable aerosol sampler was developed and evaluated in the laboratory. The new sampler is designed to be less expensive and simpler to use than existing technologies. The sampler incorporates a lightweight internal capsule fused to the sampling filter. This capsule-filter assembly allows for the inclusion of particles deposited on the internal walls and inlet, thus minimizing the need to wash or wipe the interior sampling cassette when conducting gravimetric analyses. Sampling efficiency and wall losses were tested in a low-velocity wind tunnel with particles ranging from 9.5 to 89.5 μm. The results were compared to the proposed low-velocity inhalability criterion as well as published data on the IOM sampler. Filter weight stability and time-to-equilibrium were evaluated as these factors affect the practicality of a design. Preliminary testing of the new sampler showed good agreement with both the IOM and the proposed low-velocity inhalability curve. The capsule and filter assemblies reached equilibrium within 25h of manufacturing when conditioned at elevated temperatures. After reaching equilibrium, the capsule-filter assemblies were stable within 0.01mg.

Sampling efficiency of modified 37-mm sampling cassettes using computational fluid dynamics

ABSTRACT In the U.S., most industrial hygiene practitioners continue to rely on the closed-face cassette (CFC) to assess worker exposures to hazardous dusts, primarily because ease of use, cost, and familiarity. However, mass concentrations measured with this classic sampler underestimate exposures to larger particles throughout the inhalable particulate mass (IPM) size range (up to aerodynamic diameters of 100 μm). To investigate whether the current 37-mm inlet cap can be redesigned to better meet the IPM sampling criterion, computational fluid dynamics (CFD) models were developed, and particle sampling efficiencies associated with various modifications to the CFC inlet cap were determined. Simulations of fluid flow (standard k-epsilon turbulent model) and particle transport (laminar trajectories, 1–116 μm) were conducted using sampling flow rates of 10 L min−1 in slow moving air (0.2 m s−1) in the facing-the-wind orientation. Combinations of seven inlet shapes and three inlet diameters were evaluated as candidates to replace the current 37-mm inlet cap. For a given inlet geometry, differences in sampler efficiency between inlet diameters averaged less than 1% for particles through 100 μm, but the largest opening was found to increase the efficiency for the 116 μm particles by 14% for the flat inlet cap. A substantial reduction in sampler efficiency was identified for sampler inlets with side walls extending beyond the dimension of the external lip of the current 37-mm CFC. The inlet cap based on the 37-mm CFC dimensions with an expanded 15-mm entry provided the best agreement with facing-the-wind human aspiration efficiency. The sampler efficiency was increased with a flat entry or with a thin central lip adjacent to the new enlarged entry. This work provides a substantial body of sampling efficiency estimates as a function of particle size and inlet geometry for personal aerosol samplers.

Assessment of increased sampling pump flow rates in a disposable, inhalable aerosol sampler

ABSTRACT A newly designed, low-cost, disposable inhalable aerosol sampler was developed to assess workers personal exposure to inhalable particles. This sampler was originally designed to operate at 10 L/min to increase sample mass and, therefore, improve analytical detection limits for filter-based methods. Computational fluid dynamics modeling revealed that sampler performance (relative to aerosol inhalability criteria) would not differ substantially at sampler flows of 2 and 10 L/min. With this in mind, the newly designed inhalable aerosol sampler was tested in a wind tunnel, simultaneously, at flows of 2 and 10 L/min flow. A mannequin was equipped with 6 sampler/pump assemblies (three pumps operated at 2 L/min and three pumps at 10 L/min) inside a wind tunnel, operated at 0.2 m/s, which has been shown to be a typical indoor workplace wind speed. In separate tests, four different particle sizes were injected to determine if the samplers performance with the new 10 L/min flow rate significantly differed to that at 2 L/min. A comparison between inhalable mass concentrations using a Wilcoxon signed rank test found no significant difference in the concentration of particles sampled at 10 and 2 L/min for all particle sizes tested. Our results suggest that this new aerosol sampler is a versatile tool that can improve exposure assessment capabilities for the practicing industrial hygienist by improving the limit of detection and allowing for shorting sampling times.

Laboratory evaluation of a low-cost, real-time, aerosol multi-sensor

ABSTRACT Exposure to occupational aerosols are a known hazard in many industry sectors and can be a risk factor for several respiratory diseases. In this study, a laboratory evaluation of low-cost aerosol sensors, the Dylos DC1700 and a modified Dylos known as the Utah Modified Dylos Sensor (UMDS), was performed to assess the sensors’ efficiency in sampling respirable and inhalable dust at high concentrations, which are most common in occupational settings. Dust concentrations were measured in a low-speed wind tunnel with 3 UMDSs, collocated with an aerosol spectrometer (Grimm 1.109) and gravimetric respirable and inhalable samplers. A total of 10 tests consisting of 5 different concentrations and 2 test aerosols, Arizona road dust and aluminum oxide, were conducted. For the Arizona road dust, total particle count was strongly related between the spectrometer and the UMDS with a coefficient of determination (R2) between 0.86–0.92. Particle count concentrations measured with the UMDS were converted to mass and also were related with gravimetrically collected inhalable and respirable dust. The UMDS small bin (i.e., all particles) compared to the inhalable sampler yielded an R2 of 0.86–0.92, and the large bin subtracted from the small bin (i.e., only the smallest particles) compared to the respirable sampler yielded an R2 of 0.93–0.997. Tests with the aluminum oxide demonstrated a substantially lower relationship across all comparisons. Furthermore, assessment of intra-instrument variability was consistent for all instruments, but inter-instrument variability indicated that each instrument requires its own calibration equation to yield accurate exposure estimates. Overall, it appears that the UMDS can be used as a low-cost tool to estimate respirable and inhalable concentrations found in many workplaces. Future studies will focus on deployment of a UMDS network in an occupational setting.

Performance of prototype high-flow inhalable dust sampler in a livestock production facility

ABSTRACT A high-flow inhalable sampler, designed for operational flow rates up to 10 L/min using computer simulations and examined in wind tunnel experiments, was evaluated in the field. This prototype sampler was deployed in collocation with an IOM (the benchmark standard sampler) in a swine farrowing building to examine the sampling performance for assessing concentrations of inhalable particulate mass and endotoxin. Paired samplers were deployed for 24 hr on 19 days over a 3-month period. On each sampling day, the paired samplers were deployed at three fixed locations and data were analyzed to identify agreement and to examine systematic biases between concentrations measured by these samplers. Thirty-six paired gravimetric samples were analyzed; insignificant, unsubstantial differences between concentrations were identified between the two samplers (p = 0.16; mean difference 0.03 mg/m3). Forty-four paired samples were available for endotoxin analysis, and a significant (p = 0.001) difference in endotoxin concentration was identified: the prototype sampler, on average, had 120 EU/m3 more endotoxin than did the IOM samples. Since the same gravimetric samples were analyzed for endotoxin content, the endotoxin difference is likely attributable to differences in endotoxin extraction. The prototypes disposable thin-film polycarbonate capsule was included with the filter in the 1-hr extraction procedure while the internal plastic cassette of the IOM required a rinse procedure that is susceptible to dust losses. Endotoxin concentrations measured with standard plastic IOM inserts that follow this rinsing procedure may underestimate the true endotoxin exposure concentrations. The maximum concentrations in the study (1.55 mg/m3 gravimetric, 2328 EU/m3 endotoxin) were lower than other agricultural or industrial environments. Future work should explore the performance of the prototype sampler in dustier environments, where concentrations approach particulates not otherwise specified (PNOS) limits of 10 mg/m3, including using the prototype as a personal sampler.

A comparison of the closed-face cassette at different orientations while measuring total particles.

The current method for sampling aerosols using the 37-mm closed-face cassette (CFC) sampler is based on the orientation of the cassette at ∼45° from horizontal. There is some concern as to whether this method is appropriate and may be underestimating exposures. An alternative orientation at ∼0° (horizontal) has been discussed. This research compared the CFCs orientation at 45° from horizontal to the proposed orientation at horizontal, 0° in a controlled laboratory setting. The particles used in this study were fused alumina oxide in four sizes, approximately 9.5 μm, 12.8 μm, 18 μm, and 44.3 μm in aerodynamic diameter. For each test, one aerosol was dispersed in a wind tunnel operating at 0.2 m/s with samplers mounted in the breathing zone of a rotating mannequin. A sampling event consisted of four pairs of samplers, placed side by side (one pair at 45° and another at 0° cassette orientation), and exposed for a period of 45 minutes. A total of 12 sampling events, 3 sample events per particle size, were conducted with a total of 94 samples collected. Mass concentration measurements were compared to assess the relationship between the sampler orientations of the cassettes. In addition, the relationship between the mass collected on the cassette filter and on the interior walls of the cassette was also assessed. The results indicated that there was no significant difference between the measured concentrations based on the orientation of the CFCs. The amount of mass collected on the interior walls of the cassettes was relatively low (<5%) compared to expected (up to 100%) wall losses for both orientations.