The objective of this pilot study was to determine the minimum operational flow for loose-fitting powered air-purifying respirators (PAPR) used in healthcare cleaning services. An innovative respiratory flow recording device was worn by nine healthcare workers to obtain the minute volume (MV, L/min), mean inhalation flow (MIF, L/min), and peak inhalation flow (PIF, L/min) while performing “isolation unit work” (cleaning and disinfecting) of a patient room within 30 min. The MV and PIF were compared with the theoretical values obtained from an empirical formula. The correlations of MV, MIF, and PIF with subjects’ age, weight, height, body surface area (ADu), and body mass index (BMI) were analyzed. The average MV, MIF, and PIF were 33, 74, and 107 L/min, with maximal airflow rates of 41, 97, and 145 L/min, respectively, which are all below the current 170 L/min minimum operational flow for NIOSH certified loose-fitting PAPRs.

OBJECTIVESNational Institute for Occupational Safety and Health-approved P100 filtering facepiece respirators (FFRs) have a higher filter efficiency compared to the N95 filters. However, the former typically produce higher flow resistance (Rf). Consequently, when faceseal leakage is present, the proportion of leakage airflow for P100 FFRs may exceed that of N95s, resulting in a higher total inward leakage (TIL) of the P100.METHODSIn this manikin-based study, the performance of two pairs of N95 and P100 FFRs (N95-A versus P100-A; N95-B versus P100-B) were compared under five sealing conditions (fully sealed and partially sealed with one, two, or three leaks of 0.8-mm, and one 2-mm leak). Sodium chloride particles (CMD ~45 nm) were used as the challenge aerosol. Respirators were tested under three constant flows (15, 50, and 85 L/min) and three cyclic flows (mean inspiratory flow = 15, 50, and 85 L/min). Both filter penetration (Pfilter) and TIL were determined. The Rf under constant flows was recorded. Based on Pfilter, TIL, and Rf, the quality factor (qf) was calculated to compare the overall performance of N95 and P100 FFRs.RESULTSFor a fully sealed condition, the Pfilter was much lower for the P100 FFRs than for the N95 FFRs. When small leaks were inserted (0.8-mm and 2 × 0.8-mm), the TIL was higher for the P100 FFRs than for the N95 FFRs under the lowest tested flow (15 L/min), while for greater leaks (3 × 0.8-mm and 2-mm), the TIL of the P100 FFRs was always higher regardless of the flow. The Rf of P100 FFRs was measured twice as high as the N95. The qf values were also found higher for the N95 FFRs than for the P100 FFRs regardless of leak size and breathing flow.CONCLUSIONSWith the presence of artificial leakage, a P100 FFR with high-flow-resistance may not be as protective as a low-flow-resistance N95 FFR. This finding suggests that future efforts should be directed to reducing the breathing resistance when designing P100 FFRs.

Capture hoods are an important component of a local ventilation system designed to reduce exposures to airborne contaminants. The velocity at any point along the centerline of the hood (V-x) is currently estimated using one of many predictive equations developed since the 1930s. It is unproven that those predictive equations for V-x are accurate, despite the prodigious number of studies concerning them. Among other issues, almost all experimental verifications were conducted for conditions that were either unrealistically ideal without competing air currents (e.g., zero cross draft) or were not described.This study measured values of V-x along the midline using Particle Image Velocimetry (PIV) at distances of 1-14 inches in front of a rectangular capture hood. The experiments were conducted in a large wind tunnel (9 x 12 x 40, H x W x L) using a heated, breathing, anthropomorphically sized manikin. Three 0 degree draft velocities (V-draft = 4, 14, and 50ft/min) were tested, all directed toward the hood face and the back of the manikin (if present). For each value of V-draft, the velocity fields were measured in a factorial design with and without the manikin, and with and without a worktable underneath the hood. An ideal condition was represented by a freestanding hood at the 4 fpm draft. Nonideal conditions included the presence of a worktable or manikin, and the combination of table and manikin. Each condition was tested at the three levels of V-draft.The experimental results found significant effects (p < 0.001) for V-draft, the presence of the manikin, the presence of the worktable, and all combinations of those factors. The effects of the independent variables were most pronounced at distances greater than 10 in (25.4cm) from the hood face. It is concluded that none of the previously published models accurately predicted V-x under the realistic conditions tested in this study. A satisfactory model will have to include terms for V-draft and the presence of a worktable and a worker.

Background In the field of respiratory protection for healthcare workers (HCWs), few data are available on respiratory airflow rate when HCWs are performing their work activities. The objective of this study was to assess the performance of two wearable breathing recording devices in a simulated healthcare environment. Methods Breathing recording devices from two different manufactures "A" and "B" were assessed using 15 subjects while performing a series of simulated healthcare work activities (patient assessment; vitals; IV treatment; changing linen; carrying weight while walking; normal breathing while standing). The minute volume (MV, L/min), mean inhalation flow (MIF, L/min), peak inhalation flow (PIF, L/min), breathing frequency (f, breaths/min), and tidal volume (TV, L/min) measured by each device were analyzed. Bland-Altman method was applied to explore the variability of devices A and B. Duncan's multiple range test was used to investigate the differences among activity-specific inspiratory flow rates. Results The average MV, MIF and PIF reported by device A were 23, 54, and 82 L/min with 95% upper confidence intervals (CIs) of 25, 60 and 92 L/min; the mean differences of MV, MIF and PIF presented by the two units of device A were 0.9, 1.3, and 2.8 L/min, respectively. The average values and mean differences of MV, MIF and PIF found with device B were significantly higher than device A (P<0.05), showing a high variability. During non-speech activities, the PIF/MV and MIF/MV ratios were >3.14 and >2, while with speech, the ratios increased to >6 and >3. The f during speech (15 breaths/min) was significantly lower than non-speech activities (20-25 breaths/min). Among different simulated work activities, the PIF of "patient assessment" was the highest. Conclusions This study demonstrated a novel approach to characterize respiratory flow for healthcare workers using an innovative wearable flow recording device. Data from this investigation could be useful in the development of future respirator test standards.

This study was to determine occupational exposures to formaldehyde and to compare concentrations of formaldehyde obtained by active and passive sampling methods. In one pathology and one histology laboratories, exposure measurements were collected with sets of active air samplers (Supelco LpDNPH tubes) and passive badges (ChemDisk Aldehyde Monitor 571). Sixty-six sample pairs (49 personal and 17 area) were collected and analyzed by NIOSH NMAM 2016 for active samples and OSHA Method 1007 (using the manufacturer's updated uptake rate) for passive samples. All active and passive 8-hr time-weighted average (TWA) measurements showed compliance with the OSHA permissible exposure limit (PEL-0.75 ppm) except for one passive measurement, whereas 78% for the active and 88% for the passive samples exceeded the NIOSH recommended exposure limit (REL-0.016 ppm). Overall, 73% of the passive samples showed higher concentrations than the active samples and a statistical test indicated disagreement between two methods for all data and for data without outliers. The OSHA Method cautions that passive samplers should not be used for sampling situations involving formalin solutions because of low concentration estimates in the presence of reaction products of formaldehyde and methanol (a formalin additive). However, this situation was not observed, perhaps because the formalin solutions used in these laboratories included much less methanol (3%) than those tested in the OSHA Method (up to 15%). The passive samplers in general overestimated concentrations compared to the active method, which is prudent for demonstrating compliance with an occupational exposure limit, but occasional large differences may be a result of collecting aerosolized droplets or splashes on the face of the samplers. In the situations examined in this study the passive sampler generally produces higher results than the active sampler so that a body of results from passive samplers demonstrating compliance with the OSHA PEL would be a valid conclusion. However, individual passive samples can show lower results than a paired active sampler so that a single result should be treated with caution.

BACKGROUND:The coal mining industry relies heavily on a hearing protector (HP) for noise protection. Researchers suggested that individual HP fit tests be conducted to estimate the noise attenuation.OBJECTIVE:This study examined whether individual fit tests accurately predicted workers' ear plug noise protection while working and whether the real-time noise reduction (NR) remained constant in mining work while an ear plug was worn.METHODS:A total of 11 subjects from 3 coal mines each was fit tested using the microphone-in-real-ear (MIRE) technique on their E-A-Rtrademark earplugs in a typical mine office. The same fit tested miners each wore the same type of earplugs in his usual manner doing his normal work. The minute-by-minute real-time NRwork values were determined continuously during full shifts of work.RESULTS AND CONCLUSIONS:Results showed there was a modest prediction relationship (R2 = 0.53) between NRfit and NRwork. NRwork values of each miner's earplug fluctuated over 20 dBA while the earplug was worn. However, each was still able to achieve an average NRwork of more than 10 dBA, indicating the earplug was somewhat effective in reducing noise, if worn. Refitting was an important cause of the low NRwork values. Low-frequency noise sources might be also important causes.

At present exposure limits, one in four workers will develop a permanent hearing loss as a result of mining coal (Prince 1997). Mine Safety and Health Administration (MSHA) inspectors found in the period of 1986-1992 that approximately 25% of coal miners' daily noise doses exceeded MSHA's PEL. Virtually all mines have hearing conservation programs and virtually all miners are issued and told to wear either ear muffs or ear plugs. Nevertheless, miners still have a high rate of noise induced hearing loss (NIHL). An important question is to what degree the ineffectiveness of hearing conservation programs is due to failure of miners to wear muffs and plugs properly when they are needed and how much is due to inadequacies of hearing protectors. If the former is important, can technological innovations provide means to improve use of muffs and plugs. If the latter is important, can individual fit-testing improve noise reduction (NR) values achieved by miners. A related issue is whether fit-testing in an office environment adequately predicts NR values achieved during work if non-wearing times are excluded. To address those issues, WVU is conducting studies in a lab and in coal mines that primarily involve measuring sound levels in the ear (SPLear) concurrently with sound levels at the shoulder (SPLsh), allowing computation of NR values for protectors.

Researchers suggested that the individual fit test be conducted to estimate the protection effectiveness of workers’ hearing protection device (HPD) while working. Practically, it is convenient to conduct single, instead of multiple, fit test measurement. This study examined if a single trial of earplug fit test can represent multiple performances. Additionally, it investigated how much noise exposure was due to the miners’ failure to wear earplugs at work. A total of 11 subjects from 3 coal mines in West Virginia in 2009 were each repeatedly fit tested using the microphone-in-real-ear technique on their earplugs. For each miner values of noise reduction (NR) were determined. The same fit tested miners each wore the earplugs doing his normal full-shift work. The real-time noise doses were determined continuously using the two dosimeters, one at the shoulder and the other under the earplug for determining potential exposure dose and the dose the ear actually received. Most subjects’ noise reduction values varied over a range of more than 10 dBA, suggesting that subjects should be fit tested with multiple donnings. Failure to wear the earplug was an important factor in determining the miners’ noise exposure, accounting for 64.6% of their doses at ear on average and ranging from 33.3 to 93.4% across these subjects. Nearly half (45.5%) of the coal miners might not receive adequate protection with their earplugs. 35.2% of miners never wore any hearing protectors in the high noise environment and were in very high risk of hearing loss. Thus, an important portion of miners were exposed to excessive noise although the earplugs were provided.

The present study concerns the flow dynamics and associated contaminant transport in the near wake of a worker using an industrial-type benchtop enclosing hood. The primary focus is on evaluating the effects on the dynamics of the wake flow and the exposure level of various extraneous factors, such as the strength and direction of cross-drafts and the worker's body heat and shape. Three-dimensional Unsteady Reynolds-Averaged Navier-Stokes simulations were carried out for a model of a simple mannequin and a model of an anthropometric mannequin. Estimated flow patterns and concentrations near the simple mannequin were compared with the observations from concurrent smoke visualization experiments and with the experimental concentration measurements, respectively. Results for both visualizations indicated that the flow in front of the worker is dominated by dynamic vortical structures and that body heat may have negative effects on the exposure level, especially at low flow rates. Using simple rounded shapes to simulate the human form was a fair approximation from the viewpoint of flow structures and exposure trends, which agreed well with the experimental measurements and observations. However, the quantitative values of the predicted concentrations in the breathing zone were sensitive to the mesh resolution. [Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplementary resource: Figures S1–S11.]

Plain benchtop enclosing hoods are assumed to be highly effective in protecting workers from airborne contaminants, but there is little research published to support or rebut that assumption. The purpose of this research was to investigate the performance of a 36 in. wide, 30 in. high, and 40 in. deep benchtop enclosing hood. The study consisted of two parts: (1) investigating the effects of hood face velocity (five levels: 111, 140, 170, 200, and 229 ft/min) and wind tunnel cross-draft velocity (five levels: 14, 26, 36, 46, and 57 ft/min) on a plain benchtop enclosing hood, and (2) studying the effects of specific interventions (no-intervention, collar flange, bottom flange, cowling, and sash) added onto the same enclosing hood. A tracer gas method was used to study the hood's performance inside a 9 ft high, 12 ft wide, and 40 ft long wind tunnel. Freon-134a concentrations were measured at the mouth and nose of an anthropometrically scaled, heated, breathing manikin holding a source between its hands while standing at the enclosing hood's face. Roughly 3 L/min of pure Freon-134a mixed with 9 L/min of helium was released from the source during all tests. Results showed that hood face velocity, wind tunnel cross-draft velocity, and interventions had statistically significant effects (p < 0.05) on the concentrations measured at the manikin's breathing zone. Lower exposures were associated with higher face velocities and higher cross-draft velocities. The highest exposures occurred when the face velocity was at the lowest test value (111 ft/min), and the cross-draft velocity was at its lowest test value (14 ft/min). For the effects of interventions to the hood face, the results showed that flanges and the cowling failed to consistently reduce exposures and often exacerbated them. However, the customized sash reduced exposures to less than the detection limit of 0.1 ppm, so a similar sash should be considered when feasible. The hood face velocity should be at least 150 ft/min if a sash is not used.

OCCUPATIONAL APPLICATIONS OCCUPATIONAL APPLICATIONS Computers with dual monitor screens are being increasingly used at many workplaces. Altered screen layout and increased viewing space associated with dual monitor screens may affect head–neck working postures and the activity of neck muscles. However, this problem has not been investigated in the past, and standard guidelines based on empirical data are not available for setting up a computer workstation with dual monitor screens. The present study compared the effects of single versus dual monitor screens on 3D head–neck postures and the activity of neck muscles in computer users. The results of this study have demonstrated that working on a video display unit workstation with dual monitor screens involved more rotated, asymmetric head–neck postures and higher activation of the anterior neck muscles than a video display unit workstation with a single monitor screen. TECHNICAL ABSTRACT Background: Among workstation design factors, placement of the computer monitor screen is the most frequently identified risk factor for neck and shoulder pain among video display unit users. One of the recent changes in video display unit workstation design that may influence the position of computer monitor screens is the use of dual monitors. Some studies have shown that user performance and efficiency was positively affected by the use of dual monitor screens; however, the effect of use of dual monitor screens on the biomechanical behavior of the head-neck region is currently unknown. Purpose: This study was aimed at understanding the effect of single versus dual monitor screens on 3D head–neck postures and the activity of neck muscles. Method: Ten healthy participants performed three types of video display unit tasks: (1) reading for 10 minutes, (2) typing for 5 minutes, and (3) performing search and find tasks for 10 minutes using single and dual monitor screens. An inertial motion-capture system was used to measure 3D head–neck postures. Activity of sternocleidomastoid and cervical trapezius muscles was recorded bilaterally using surface electromyography. Results: Use of dual monitor screens significantly increased head–neck rotation by 9.0° compared to the single monitor screen. The range of motion of head–neck rotation increased significantly by 8.4° using dual monitor screens compared to the single monitor screen. Corresponding to the increase in the head–neck rotation, a contralateral increase in the activity of the right sternocleidomastoid muscle was observed with the dual monitor screen layout. Activity of cervical trapezius muscle was not affected by the type of monitor layout. Conclusions: Increased activation of anterior neck muscles caused by asymmetrical, more rotated head–neck postures while operating a video display unit workstation with dual monitor screens may increase the risk of neck musculoskeletal disorders, especially with prolonged computer use. KEYWORDS: Video display unit workstationdual monitor screensneck muscles electromyography3D head–neck postures ACKNOWLEDGMENTS Sincere thanks to the anonymous reviewers for their invaluable comments to improve this article.

The purpose of this study was to explore the influence of individual personality on the biomechanical response of neck and shoulder muscles to physical and psychosocial demands. Eighteen healthy male participants performed isometric pulling exertions in a semi-standing posture in the presence and absence of mentally demanding tasks. Surface electromyography (EMG) was used to quantify biomechanical response of neck and shoulder muscles, and the NASA Task Load Index (TLX) was used for subjective workload assessment. The effect of individual personality as a potential modifier was evaluated by classifying participants into thinking and feeling personality types. Mentally demanding tasks performed prior to the physical exertions significantly affected the muscle loading during the physical exertion. Activation of the shoulder as well as neck muscles increased with the addition of mental stress. Higher workload scores for mental and temporal demands, and frustration were reported by the participants during combined physical and mental tasks. In general, participants with feeling personality showed higher increase in the muscle activation level than participants with thinking personality corresponding to identical mental and physical demands, which indicate that response to mental stress during physically demanding tasks seems to be mediated by the individual personality.Relevance to industry: Work environments in modern work places, with strong emphasis on efficiency, competitiveness, and downsizing, are characterized by a combination of physical and psychosocial demands. Individual factors such as personality traits are known to interact with these work-related factors to reconcile or aggravate the body's biomechanical response, yet the interacting effect of these factors on muscular loading is not clearly understood. The results of this study indicate that certain personalities are more vulnerable than others to increased muscle loading in response to mental stress during physically demanding tasks. (C) 2012 Elsevier B.V. All rights reserved.

Effective hoods are critical for the protection of workers from airborne contaminants. The aim of this study is to determine the effects of cross-draft and presence of a worker on the effectiveness of the bench-top enclosing hoods, which, unlike laboratory fume hoods have no sash and have a constant cross-sectional area. The computational fluid dynamics (CFD) software, FLUENT, with shear-stress transport (SST) k-ω turbulence model was used to investigate the effect of orientation of the manikin and hood with respect to cross-draft on the flow and contaminant concentration field. Experiments were conducted using a manikin and a fume hood in a wind tunnel and the flow around the manikin and inside the hood was investigated via particle image velocimetry (PIV) measurements. The correlation of contaminant leakage with the turbulent intensity and recirculating vortices at the hood face were observed. The hood and manikin orientation was found to change the exposure level significantly. Maximum contaminant leakage from the hood to the working environment has been found when the hood and manikin were placed 30 degrees to the cross draft. Maximum containment was observed when the manikin and hood were oriented in the same direction as the cross draft and perpendicular to the cross draft.

BACKGROUND:Inhalation of diesel particulate matter (DPM) is known to have a negative impact on human health. Consequently, there are regulations and standards that limit the maximum concentrations to which persons may be exposed and the maximum concentrations allowed in the ambient air. However, these standards consider steady exposure over large spatial and time scales. Due to the nature of many vehicle exhaust systems, pedestrians in close proximity to a vehicle's tailpipe may experience events where diesel particulate matter concentrations are high enough to cause acute health effects for brief periods of time.METHODS:In order to quantify these exposure events, instruments which measure specific exhaust constituent concentrations were placed near a roadway and connected to the mouth of a mannequin used as a pedestrian surrogate. By measuring concentrations at the mannequin's mouth during drive-by events with a late model diesel truck, a representative estimate of the exhaust constituent concentrations to which a pedestrian may be exposed was obtained. Typical breathing rates were then multiplied by the measured concentrations to determine the mass of pollutant inhaled.RESULTS:The average concentration of diesel particulate matter measured over the duration of a single drive-by test often exceeded the low concentrations used in human clinical studies which are known to cause acute health effects. It was also observed that higher concentrations of diesel particulate matter were measured at the height of a stroller than were measured at the mouth of a mannequin.CONCLUSION:Diesel particulate matter concentrations during drive-by incidents easily reach or exceed the low concentrations that can cause acute health effects for brief periods of time. For the case of a particularly well-tuned late-model year vehicle, the mass of particulate matter inhaled during a drive-by incident is small compared to the mass inhaled daily at ambient conditions. On a per breath basis, however, the mass of particulate matter inhaled is large compared to the mass inhaled at ambient conditions. Finally, it was determined that children, infants, or people breathing at heights similar to that of a passing vehicle's tailpipe may be exposed to higher concentrations of particulate matter than those breathing at higher locations, such as adults standing up.

Active noise control (ANC) works best to reduce low frequency noise. Because many industrial noise sources are broadband, ANC may be used more if it can be successfully applied to higher frequency ranges. This study explored one method to increase ANC effectiveness at higher frequencies. ANC is particularly useful in hard-walled ducts where plane waves propagate. Higher order mode waves are much more difficult to control. Basic acoustic principles dictate that the cut-on frequency at which higher order modes will first begin to eclipse simple plane waves in a duct will be determined by the cross-sectional geometry of the duct. The lowest frequency for higher order modes increases as duct diameter decreases; therefore the range of frequencies where plane waves dominate will be greater and effective control using ANC will be better as duct diameter decreases. The result is that somewhat higher frequencies can be controlled with ANC for smaller diameters. Below the first higher order mode cut-on frequency for the largest size studied, there should be little difference in ANC effectiveness between the duct sizes. To test those suppositions, a commercially available ANC system was used to reduce random noise in rectangular and round ducts having different diameters. Results showed that insertion loss (IL) ranged from 5 dB to 29 dB in frequencies ranging from 40–1000 Hz and varied inversely with cross-sectional size as expected. There was no difference in IL below 280 Hz (p = 0.7751) between the different diameter ducts. There was a significant difference between duct diameters above 280 Hz (p < 0.0001). The same tests were conducted on a rectangular duct with one cross-sectional dimension fixed and one varied at seven different sizes. Results showed similar IL from 5 dB to 29 dB that varied inversely with size.

This study tested the "Target Method" for adjusting ventilation systems. The Target Method is based on target hood static pressures (SPh(target)) computed in a manner designed to take into account the estimated effects of dampers on the fan, the order of damper adjustments, and the ratio of the prebalancing branch airflows to their goals. It is aimed at achieving a desired relative distribution of airflows even if the fan output is far from ideal. The method assumes the fan output will be adjusted after the dampers are adjusted. The method is expected to produce lower fan pressure requirements than some commonly used methods. The method was tested on a working seven-branch, full-sized exhaust ventilation system in the West Virginia University Exposure Assessment Laboratory. Two radically different target distributions were tested with two replications apiece. Both target distributions of airflows were substantially different from the initial distribution, providing a high degree of challenge to the methodology. For each distribution, SPh(target) values were computed for the first round of adjustments. Each damper was adjusted until the observed value of the hood static pressure was nearly equal to that damper's computed SPh(target) value for that distribution. Each of the other branch dampers was adjusted similarly in turn. After the first round of adjustments, the median ratio of SPh to SPh(target) provided the targets for the partial second round of adjustments. Twenty-point Pitot traverses were used to determine the airflow in each branch duct both before and after employing the adjustment method, providing the basis to determine the success in reaching each of the two desired distributions. The percentage of excess airflow (assuming ideal adjustment of the fan speed) was below 2.2% for all experimental trials. An unpublished study by Vivek Balasubramanian showed that excess airflow was 4.8% to 8.5% in the same experimental system after two full rounds of adjustment using the customary Target Method. Under poor measurement conditions, the greater uncertainty of pressure measurements would likely produce somewhat higher excess airflows.

Active noise control ( ANC) is particularly useful in hard-walled ducts where plane waves propagate. Higher order mode waves are much more difficult to control. Basic acoustic principles dictate that the cut-on frequency at which higher order modes will first begin to eclipse simple plane waves in a duct will be determined by the cross-sectional diameter of the duct. The lowest frequency for higher order modes will increase as duct diameter decreases. Therefore, the range of frequencies where plane waves dominate will be greater, and effective control using ANC will be better as duct diameter decreases. The result is that somewhat higher frequencies can be controlled with ANC for smaller diameters. If smaller diameters have broader frequency ranges that can be controlled with ANC, perhaps one could extend the frequency range for a large cross section by partitioning it into smaller cross sections using axial vane splitters. This hypothesis was tested by two methods of cross-sectional partitioning. Partitioning was achieved in one design by inserting a smaller duct inside a large duct. In a second design, a cross-shaped splitter was inserted inside the large duct. Summed ANC insertion loss ( IL) at low frequencies (<= 250 Hz) was at least 16 dB and at least 14 dB at middle frequencies (>= 315 Hz). ANC IL results were 1.7 to 2 dB better for the large duct partitioned by a smaller inner duct than the large duct alone ( p= 0.0146 for low frequency and p= 0.0333 for middle frequency). ANC insertion loss was 5.6 dB better for the large duct partitioned by a cross-shaped splitter at high frequencies than the large duct alone ( p = 0.0003). However, the cross-shaped partition system was 5.8 dB less effective at low frequencies than the large duct ANC IL alone ( p< 0.0001).

Three-dimensional computational fluid dynamics simulations are used to investigate the distribution and level of contaminant concentrations in the true breathing zone (at the nose and mouth) when toxic airborne contaminants are released within an arm's length in front of the worker who has his back to the airflow. The effects of different body shapes on fluid flow and concentration patterns around the body in a wind tunnel were evaluated and clarified that a sharp body or a block may not be a good surrogate for the human form in consideration of occupational and environmental health studies. The comparison of the concentration field calculated with the Eulerian and Lagrangian methods revealed that the Eulerian method has a more diffusive nature than the Lagrangian method. The concentrations at different locations were also compared to determine the optimum sampling location. It was found that the concentration at the breathing zone may be significantly different from the one at the chest area. The influence of the heat flux from the body was studied at two different Reynolds numbers. Predictions indicate that the heat flux may have a significant impact on exposure especially when the convection induced by buoyancy dominates the flow.

The present work is concerned with the effect of the ventilation intensity on the worker exposure in a tunnel when the worker is facing the downstream direction and a gaseous contaminant is released in an arm length of his reach. A three-dimensional model of a manikin which was used in the experiments was created in order to study the effect of the mean inlet velocity which can be characterized by the Reynolds number based on the equivalent diameter of the head of the manikin. For this study, turbulent flow was assumed to enter the ventilation tunnel and exit at the other end from an exhaust duct. The scalar transport method was employed to determine the ethanol vapor concentration field. The results with the low_Re RNG turbulence model are compared to the ones with the RNG turbulence model. The results with the RNG k-ε turbulence model seem to agree better with the experimental data at higher Reynolds numbers. At lower Reynolds numbers there are significant differences between experiments and predictions.