Use of prototype side stream filtration system to control dust levels in a commercial swine farrowing building.

Swine meat provides an essential global food source. Due to economies of scale, modern U.S. swine production primarily occurs indoors to maintain an optimal environment across the stages of swine production. Indoor concentrations of dust and contaminant gases in swine production buildings increase in the winter months due to reduced ventilation to optimal building temperature. In this study, an engineering control technology designed to recirculate the air in a swine farrowing room through a mobile air handling unit containing high-efficiency particulate filters was presented. A mobile solution could be easily deployed as an intervention method if an infectious disease outbreak occurs at a swine operation. The performance of this control technology was evaluated following deployment in a production farrowing barn for a period of 6 weeks during the winter in the Midwestern United States. Contaminant concentrations of inhalable dust, respirable dust, and carbon dioxide were measured in the room treated by the prototype system and compared to contaminant concentrations measured in an untreated "control" room. Over 6 weeks, the mean inhalable and respirable dust concentrations observed during the study period for the "treatment" room were 2.61 and 0.14 mg/m3, respectively, compared to 3.51 and 0.25 mg/m3, respectively, for the control room. The mobile recirculating ventilation system, operating at a flow rate of 45 m3/min (5 room air exchanges per hour), reduced the inhalable dust by 25% and respirable dust by 48% as measured with a real-time aerosol monitor, when compared to the control room. In addition, no concentration differences in carbon dioxide and relative humidity between the treatment and the control rooms were observed. Inhalable and respirable concentrations of dust were significantly reduced (p = 0.001), which demonstrates an essential improvement of the air quality that may prove beneficial to reduce the burden of disease among both workers and animals.

Evaluation of hearing protection device effectiveness for musicians.

OBJECTIVE: To evaluate musicians' personal attenuation and perceptions of three types of hearing protection devices (HPDs): formable foam earplugs and both non-custom and custom versions of uniform attenuation earplugs (UAEs) marketed to musicians. DESIGN: A mixed-methods approach was used to evaluate the HPDs. Audiometric testing obtained hearing levels at baseline and with each HPD across frequencies (125-8000 Hz) to determine personal attenuation ratings and uniformity of attenuation. Participants completed surveys over six months regarding how often they used the HPDs and their perceptions about wearing them. STUDY SAMPLE: Twenty-four musicians were recruited to participate. RESULTS: Substantial variability was observed in the attenuation achieved among participants for each HPD type, but custom UAEs provided the most consistent attenuation across frequencies. Participants' HPD preferences were influenced by multiple factors including personal instrument and specific activity. Custom UAEs were most frequently used but usage rates continually decreased over the 6-month period. CONCLUSIONS: Fit-testing is important to determine fit and sizing. Combining information on the effectiveness of HPDs with musicians' opinions about wearing them can inform recommendations for which types may be the most effective and feasible options for reducing sound exposures.

Development of a Checklist to Identify Injury Hazards on Row Crop Farms in the Midwestern United States.

Agriculture is among the most dangerous industries in the U.S., yet routine surveillance of injury hazards is not currently being conducted on a national level. The objectives of this study were to describe a new tool, called the Hazard Assessment Checklist (HAC), to identify and characterize farm hazards that increase injury risk to farmers and farm workers, and (2) report the inter-rater reliability of the new tool when administered on row-crop farms in Iowa. Based on a literature review and a consensus of expert opinion, the HAC included hazards related to self-propelled vehicles, powered portable implements, fixed machinery and equipment, farm buildings and structures, fall risks, and portable equipment associated with fall risk. A scoring metric indicating the extent of compliance with recommended safety guidelines and standards was developed for each item of the HAC, which included compliant, minimal improvement needed, substantial improvement needed, and not compliant. Inter-rater reliability was assessed from data collected by research staff on 52 row crop farms in Iowa. Cohen's weighted Kappa values demonstrated high inter-rater reliability, ranging between 0.86 and 0.94, for all HAC sections. The HAC can be completed in 1.5-2 hours on each farm and requires about three hours of training, two hours of which are spent in field training. The ability to monitor injury-related hazards over time using an empirically driven tool will contribute significantly to injury prevention efforts in an industry with consistently high rates of fatal and nonfatal injury.

Assessment of respirable aerosol concentrations using local ventilation controls in an open multi-chair dental clinic.

Dental procedures require patients to be unmasked throughout most of a dental visit, with some procedures generating both inhalable and respirable aerosols. Understanding aerosol generation and transport were important to developing protocols to protect both the patient and workers in dental environments early in the COVID pandemic. This study investigated the need, suitability, and effectiveness of using local exhaust ventilation units during patient procedures and examined the impact of patient density in a large, multi-chair dental clinic at an academic institution. Phase One measured respirable aerosol concentrations at the dental assistant's breathing zone and in neighboring unoccupied patient operatories. Results were compared during four dental procedures with three local ventilation (LV) options, with a single faculty performing procedures on a simulated patient. Phase Two deployed LV in all active patient operatories during procedures on actual patients and examined the impact of clinic patient occupancy on respirable aerosol concentrations throughout the clinic. During Phase One, respirable aerosol concentrations in nearby operatories were significantly higher during ultrasonic scaling (mean = 3.8 and SD = 0.3 µg/m3) and lower during rubber cup polishing (mean = 0.8 and SD = 0.5 mg/m3) (p < 0.001). While the same trend was identified for the dental assistant, differences were not significant. There was no difference in respirable aerosol concentrations by LV type when measured at the dental assist (p = 0.51, task means 3 to 32. 5 µg/m3) or neighboring rooms (p = 0.93, task means 0.6 to 4.0 µg/m3), indicating no improved control for any device tested. For Phase Two, the clinic deployed the extraoral suction (EOS) system in each patient operatory. The background-adjusted aerosol concentrations were significantly reduced (F < 0.001) when the operatories were occupied at 50% compared to 25%, likely attributed to increased air filtration of the room with double the EOS systems in use. While this study provides only a single case investigation, findings confirming respirable aerosol concentrations by procedure and across days provided insights into patient scheduling, local exhaust ventilation selection, and operation, which could be useful to other open multi-chair dental clinics.

Assessment of university classroom ventilation during the COVID-19 pandemic.

Ventilation plays an important role in mitigating the risk of airborne virus transmission in university classrooms. During the early phase of the COVID-19 pandemic, methods to assess classrooms for ventilation adequacy were needed. The aim of this paper was to compare the adequacy of classroom ventilation determined through an easily accessible, simple, quantitative measure of air changes per hour (ACH) to that determined through qualitative "expert judgment" and recommendations from the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), and the American Conference of Governmental Industrial Hygienists (ACGIH)®. Two experts, ventilation engineers from facilities maintenance, qualitatively ranked buildings with classrooms on campus with regard to having "acceptable classroom ventilation." Twelve lecture classrooms were selected for further testing, including a mix of perceived adequate/inadequate ventilation. Total air change per hour (ACH) was measured to quantitatively assess ventilation through the decay of carbon dioxide in the front and rear of these classrooms. The outdoor ACH was calculated by multiplying the total ACH by the outdoor air fraction. The classrooms in a building designed to the highest ASHRAE standards (62.1 2004) did not meet ACGIH COVID-19 recommendations. Four of the classrooms met the ASHRAE criteria. However, a classroom that was anticipated to fail based on expert knowledge met the ASHRAE and ACGIH criteria. Only two classrooms passed stringent ACGIH recommendations (outdoor ACH > 6). None of the classrooms that passed ACGIH criteria were originally expected to pass. There was no significant difference in ACH measured in the front and back of classrooms, suggesting that all classrooms were well mixed with no dead zones. From these results, schools should assess classroom ventilation considering a combination of classroom design criteria, expert knowledge, and ACH measurements.

Assessment of occupational personal sound exposures for music instructors.

Daily activities performed by music instructors generate high sound levels that could potentially lead to overexposure. Adverse outcomes associated with high-exposure to sound, such as hearing loss and tinnitus, can be especially devastating to music instructors as hearing is essential to both job performance and career reward. The primary objective of this study was to compare sound exposures of music instructors to recommended exposure limits. Secondary objectives were to identify high-exposure activities and to evaluate potential similar exposure groups by examining between- and within-worker exposure variability. Personal sound exposure measurements from music instructors were collected using dosimeters during full workdays for up to 4 weeks over multiple semesters at a university's school of music. Study participants completed an activity log to record work-related activities throughout each day of sampling. Dosimeters logged 1-sec sound equivalent levels in A-weighted decibels. These data were used to calculate 8-hr time-weighted averages, daily dose, and activity-specific contributions to that dose to determine if daily exposures exceeded the recommended limit of 85 dBA and to identify high-exposure activities that could be targeted for future intervention. Seventeen participants were sampled for a total of 200 days. Approximately one-third of daily exposures exceeded recommended limits. The groups with the highest exposures were brass and conducting instructors. Conductors experienced the highest between-day variability in daily exposures. Activities that contributed the most to daily dose included group rehearsals, personal practice sessions, and performances, while classes and administrative work did not substantially contribute to daily dose. Daily exposures were highly variable, ranging from 60-95 dBA (mean = 81 dBA, sd = 8 dBA), and were influenced by instructional area and musical activity. Future exposure assessments for music instructors should include sampling for multiple days, and those above-recommended limits should be placed into hearing conservation programs.

Assessing Health and Safety Concerns and Psychological Stressors among Agricultural Workers in the U.S. Midwest.

There is limited research exploring agricultural workers' own perspectives on the relative importance of the hazards and stressors they experience. There is also a lack of evidence on whether this reporting differs by method of elicitation. Finally, very little research exists on how to improve mail survey response rates among agricultural workers. We examined health and safety concerns and psychological stressors among Midwestern farmers. We assessed whether these reports varied by survey mode (mail survey versus in-person survey). The efficacy of two different types of incentives to enhance mail survey response rates among agricultural workers was also investigated. In 2018, a needs assessment survey was developed and mailed to a random sample of farm owner-operators in Iowa, Ohio, and Missouri, with randomly assigned prepaid or promised monetary incentives. In-person surveys were conducted among farm owner-operators and hired workers at three regional farm shows in Iowa, Minnesota, and Nebraska. The mail survey response rates were compared by incentive type. Content analysis was used to generate themes associated with health and safety concerns and psychological stressors, which were then ranked by frequency counts. Chi-square tests were used to analyze variation in the distribution of these themes by survey mode. The response rate for the $1 prepaid incentive was double that of the $10 promised incentive. Content analysis identified 13 health and safety concerns and eight psychological stressors. Chemicals, equipment/tools, and health outcomes were the most frequently noted health and safety concerns. Finances, climate/weather, and farm workload and management were the most frequently noted psychological stressors. Although there was considerable overlap in survey responses across mail and in-person respondents, important differences by sample and survey mode characteristics were observed. The results can support a variety of stakeholders in prioritizing and developing interventions and educational resources to address health and safety concerns and psychological stressors among Midwestern farmers. Our findings also contribute to the evidence base on primary data collection methods for agricultural workers.

Particle Concentrations in Occupational Settings Measured with a Nanoparticle Respiratory Deposition (NRD) Sampler.

There is an increasing need to evaluate concentrations of nanoparticles in occupational settings due to their potential negative health effects. The Nanoparticle Respiratory Deposition (NRD) personal sampler was developed to collect nanoparticles separately from larger particles in the breathing zone of workers, while simultaneously providing a measure of respirable mass concentration. This study compared concentrations measured with the NRD sampler to those measured with a nano Micro Orifice Uniform-Deposit Impactor (nanoMOUDI) and respirable samplers in three workplaces. The NRD sampler performed well at two out of three locations, where over 90% of metal particles by mass were submicrometer particle size (a heavy vehicle machining and assembly facility and a shooting range). At the heavy vehicle facility, the mean metal mass concentration of particles collected on the diffusion stage of the NRD was 42.5 ± 10.0 µg/m3, within 5% of the nanoMOUDI concentration of 44.4 ± 7.4 µg/m3. At the shooting range, the mass concentration for the diffusion stage of the NRD was 5.9 µg/m3, 28% above the nanoMOUDI concentration of 4.6 µg/m3. In contrast, less favorable results were obtained at an iron foundry, where 95% of metal particles by mass were larger than 1 µm. The accuracy of nanoparticle collection by NRD diffusion stage may have been compromised by high concentrations of coarse particles at the iron foundry, where the NRD collected almost 5-fold more nanoparticle mass compared to the nanoMOUDI on one sampling day and was more than 40% different on other sampling days. The respirable concentrations measured by NRD samplers agreed well with concentrations measured by respirable samplers at all sampling locations. Overall, the NRD sampler accurately measured concentrations of nanoparticles in industrial environments when concentrations of large, coarse mode, particles were low.

Assessment of Interventions to Improve Air Quality in a Livestock Building.

This study examined the effectiveness of engineering controls to reduce contaminant concentrations in a swine farrowing room during winter in the U.S. Midwest. Over two winters, changes in air quality were evaluated following installation of a 1700 m3 h-1 (1000 cfm) recirculating ventilation system to provide 5.4 air exchanges per hour. This system incorporated one of two readily available dust control systems, one based on filtration and the other on cyclonic treatment. A second treatment evaluated reductions in carbon dioxide (CO2) associated with replacement of standard, unvented gas-fired heaters with new vented heaters, installed between the two winter test periods. The concentrations of carbon monoxide and hydrogen sulfide were negligible in the test room. Although concentrations of ammonia increased over each winter test period, the increase was unrelated to increased air movement from the new recirculating ventilation system. The dust concentrations were significantly reduced by the ventilation system for both inhalable dust (23% to 44% with filtration, 33% with cyclone) and respirable dust (32% with filtration, 20% with cyclone), significant (p 0.024) for all except respirable dust using the cyclone (p = 0.141). The filtration unit is recommended to improve livestock building air quality because it was more effective than the cyclone unit at reducing respirable dust. Carbon dioxide concentrations were significantly lower with vented heaters (mean = 1400 ppm, SD = 330 ppm) compared to unvented heaters (mean = 2480 ppm, SD = 160 ppm). A 940 ppm reduction in CO2 was attributed to the use of the vented heater, after accounting for differences in outdoor temperatures and animal housing over both test periods. The benefits of readily available technology to significantly reduce concentrations of dust and CO2 demonstrates useful control options to improve air quality in swine buildings.

Evaluation of Low-Cost Hydrogen Sulfide Monitors for Use in Livestock Production.

Direct-reading gas monitors warn workers of the risk of potentially fatal hydrogen sulfide (H2S) exposures that may arise during manure handling. Low-cost, low-maintenance H2S monitors are available from many manufacturers, but differences in their features and performance make selection challenging for farmers. Moreover, little information is available on the practical maintenance and performance of these devices in agricultural environments. The objective of this study was to provide information to agricultural workers to aid in the selection, maintenance, and use of low-cost H2S monitors. This laboratory study evaluated the performance of several low-cost monitors over a simulated period of use of one year in a swine barn. Four models were exposed to H2S concentrations of 1 to 10 ppm over 18 weeks to examine the drift in reported concentration and changes in the alarm reaction time. Over the simulated barn year, the performance of alarm-only monitors declined faster than that of monitors displaying the H2S concentration. Of concern was the high-level (20 ppm) alarm failures after an equivalent of 139 days (Altair) and 289 days (BW Clip) in a swine barn, well within the monitor's reported shelf-life. Models displaying concentration exhibited fewer failures but were inaccurate in the displayed concentration when challenged with 20 ppm of H2S. The T40 Rattler provided consistently higher readings (+2.3 ppm), and the Pac 3500 showed consistently lower readings (-3.4 ppm) when challenged with 20 ppm. This study confirms the need for routine bump tests for these low-cost monitors to ensure that the monitor reacts to the presence of H2S, even if the manufacturer does not recommend this procedure. Most importantly, agricultural workers should inspect and bump test these monitors prior to any potentially high-risk activity, such as manure agitation, pumping, or pressure washing, to ensure that the monitor appropriately detects and warns users.

Rapid Analysis of the Size Distribution of Metal-Containing Aerosol.

Conventional methods to measure the metallic content of particles by size are time consuming and expensive, requiring collection of particles with a cascade impactor and subsequent metals analysis by inductively coupled plasma mass spectrometry (ICP-MS). In this work, we describe a rapid way to measure the size distribution of metal-containing particles from 10 nm to 20 µm, using a nano micro-orifice uniform-deposit impactor (nano-MOUDI) to size-selective and collect particles that are then analyzed with a field portable X-ray fluorescence (FP-XRF) to determine metal composition and concentration. The nano-MOUDI was used to sample a stainless-steel aerosol produced by a spark discharge system. The particle-laden substrates were then analyzed directly with FP-XRF and then with ICP-MS. Results from FP-XRF were linearly correlated with results from ICP-MS (R2 = 0.91 for Fe and R2 = 0.84 for Cr). Although the FP-XRF was unable to detect Fe particles at mass per substrate loadings less than 2.5 µg effectively, it produced results similar to those using the ICP-MS at a mass per substrate loading greater than 2.5 µg.

Simulation of air quality and operational cost to ventilate swine farrowing facilities in Midwest U.S. during winter.

We have developed a time-dependent simulation model to estimate in-room concentrations of multiple contaminants [ammonia (NH3), carbon dioxide (CO2), carbon monoxide (CO) and dust] as a function of increased ventilation with filtered recirculation for swine farrowing facilities. Energy and mass balance equations were used to simulate the indoor air quality (IAQ) and operational cost for a variety of ventilation conditions over a 3-month winter period for a facility located in the Midwest U.S., using simplified and real-time production parameters, comparing results to field data. A revised model was improved by minimizing the sum of squared errors (SSE) between modeled and measured NH3 and CO2. After optimizing NH3 and CO2, other IAQ results from the simulation were compared to field measurements using linear regression. For NH3, the coefficient of determination (R2) for simulation results and field measurements improved from 0.02 with the original model to 0.37 with the new model. For CO2, the R2 for simulation results and field measurements was 0.49 with the new model. When the makeup air was matched to hallway air CO2 concentrations (1,500 ppm), simulation results showed the smallest SSE. With the new model, the R2 for other contaminants were 0.34 for inhalable dust, 0.36 for respirable dust, and 0.26 for CO. Operation of the air cleaner decreased inhalable dust by 35% and respirable dust concentrations by 33%, while having no effect on NH3, CO2, in agreement with field data, and increasing operational cost by $860 (58%) for the three-month period.

Nonwoven textile for use in a nanoparticle respiratory deposition sampler.

The nanoparticle respiratory deposition (NRD) sampler is a personal sampler that combines a cyclone, impactor, and a nylon mesh diffusion stage to measure a worker's exposure to nanoparticles. The concentration of titanium in the nylon mesh of the diffusion stage complicates the application of the NRD sampler for assessing exposures to titanium dioxide nanoparticles. This study evaluated commercially available nonwoven textiles for use as an alternative media in the diffusion stage of the NRD sampler. Three textiles were selected as containing little titanium from an initial screening of 11 textiles by field portable x-ray fluorescence (FPXRF). Further evaluation on these three textiles was conducted to determine the concentration of titanium and other metals by inductively coupled plasma-optical emission spectroscopy (ICP-OES), the number of layers required to achieve desired collection characteristics for use as the diffusion stage in the NRD sampler (i.e., the nanoparticulate matter, NPM, criterion), and the pressure drop associated with that number of layers. Only three (two composed of cotton fibers, C1 and C2; and one of viscose bamboo and cotton fibers, BC) of 11 textiles screened had titanium concentrations below the limit of detection the XRF device (0.15 µg/cm2). Multiple metals, including small amounts of titanium, were found in each of the three nonwoven textiles using ICP-OES. The number of 25-mm-diameter layers required to achieve the collection efficiency by size required for the NRD sampler was three for C1 (R2 = 0.95 with reference to the NPM criterion), two for C2 (R2 = 0.79), and three for BC (R2 = 0.87). All measured pressure drops were less than theoretical and even the greatest pressure drop of 65.4 Pa indicated that a typical personal sampling pump could accommodate any of the three nonwoven textiles in the NRD sampler. The titanium concentration, collection efficiency, and measured pressure drops show there is a potential for nonwoven textiles to be used as the diffusion stage of the NRD sampler.

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

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 sampler's 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.

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

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 prototype's 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.

Three-dimensional computational fluid dynamics modeling of particle uptake by an occupational air sampler using manually-scaled and adaptive grids.

This work presents fluid flow and particle trajectory simulation studies to determine the aspiration efficiency of a horizontally oriented occupational air sampler using computational fluid dynamics (CFD). Grid adaption and manual scaling of the grids were applied to two sampler prototypes based on a 37-mm cassette. The standard k-ε model was used to simulate the turbulent air flow and a second order streamline-upwind discretization scheme was used to stabilize convective terms of the Navier-Stokes equations. Successively scaled grids for each configuration were created manually and by means of grid adaption using the velocity gradient in the main flow direction. Solutions were verified to assess iterative convergence, grid independence and monotonic convergence. Particle aspiration efficiencies determined for both prototype samplers were undistinguishable, indicating that the porous filter does not play a noticeable role in particle aspiration. Results conclude that grid adaption is a powerful tool that allows to refine specific regions that require lots of detail and therefore better resolve flow detail. It was verified that adaptive grids provided a higher number of locations with monotonic convergence than the manual grids and required the least computational effort.

Evaluation of a Low-Cost Aerosol Sensor to Assess Dust Concentrations in a Swine Building.

Exposure to dust is a known occupational hazard in the swine industry, although efforts to measure exposures are labor intensive and costly. In this study, we evaluated a Dylos DC1100 as a low-cost (~$200) alternative to assess respirable dust concentrations in a swine building in winter. Dust concentrations were measured with collocated monitors (Dylos DC1100; an aerosol photometer, the pDR-1200; and a respirable sampler analyzed gravimetrically) placed in two locations within a swine farrowing building in winter for 18-24-h periods. The particle number concentrations measured with the DC1100 were converted to mass concentration using two methods: Physical Property Method and Regression Method. Raw number concentrations from the DC1100 were highly correlated to mass concentrations measured with the pDR-1200 with a coefficient of determination (R (2)) of 0.85, indicating that the two monitors respond similarly to respirable dust in this environment. Both methods of converting DC1100 number concentrations to mass concentrations yielded strong linear relationships relative to that measured with the pDR-1200 (Physical Property Method: slope = 1.03, R (2) = 0.72; Regression Method: slope = 0.72, R (2) = 0.73) and relative to that measured gravimetrically (Physical Property Method: slope = 1.08, R (2) = 0.64; Regression Method: slope = 0.75, R (2) = 0.62). The DC1100 can be used as a reasonable indicator of respirable mass concentrations within a CAFO and may have broader applicability to other agricultural and industrial settings.

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

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.