Experimental and numerical studies on the impact of work practices used to control exposures occurring in booth-type hoods

Micro-environmental factors impact breathing zone exposures: A simulated petrochemical manufacturing facility task

This study investigates the impact of micro-environmental factors on worker breathing zone exposure levels in petrochemical facilities. A laboratory simulation study evaluated near-field exposure to methane for a typical maintenance task. Individual and combinations of micro-environmental factors significantly affected methane exposure. Airflow direction and speed were significant determinants of exposure concentration reduction. A side airflow direction at medium to high speed produced the lowest gas concentration in the breathing zone. Worker body orientation relative to the methane emission point was also a critical factor affecting gas concentration in the worker's breathing zone. The study provides insights into how variations in airflow and small changes in position impact near-field exposures for petrochemical tasks, guiding industrial hygiene professionals' training on qualitative exposure estimation and providing input for near-field exposure modeling to guide quantitative exposure and risk assessment.

An empirical study on the wake around a squatting worker in a confined space

OBJECTIVES

When an air current flows from behind a worker, the contaminant level in the breathing zone may increase due to the wake around the worker. Researchers have been investigating about this wake, and much knowledge has been provided about the wake that appears around a standing worker. However, the wake around a squatting worker has not been addressed. This study aimed to describe the wake in front of a worker squatting in a confined space by using a model worker and a chamber and investigate the conditions in which this wake develops easily.

METHODS

A mannequin was employed as a model worker and was placed in the chamber to simulate a squatting worker in a confined space. Then, air was sent from behind under various conditions with a fan, and the wake was observed.

RESULTS

A wake appeared when smoke was emitted at 0-0.1 m from the point just below the breathing zone, and most of the wake region was in the range between the point just below the model worker's breathing zone and body. A wake did not appear when a fan of 0.15 m in diameter was used. The flow rate and velocity of the airflow were almost irrelevant with respect to wake development.

CONCLUSIONS

The following are recommended based on the results of the present study. i) The distance between a source of contaminants and the point just below the breathing zone should be more than 0.2 m. ii) An air duct with a cross-section of less than 0.02 m(2) is desirable to avoid producing a wake.

Probabilistic model evaluation of continuous air monitor response for meeting radiation protection goals

Effective continuous air monitor (CAM) programs can eliminate or significantly reduce the amount of inhaled radioactive material following an accidental release. Numerous factors impact the levels of protection CAM programs provide to the workers during these releases. These factors range from those related to the capability of the CAM instrument (e.g., CAM alarm set point and length of counting intervals) to those related to CAM placement in the room relative to dispersion rates and patterns of the released material in a room. While the impact of many of these factors on alarm sensitivity has been investigated in isolation, there are no methods for holistic evaluations of CAM programs relative to radiation protection goals (RPGs) or the contribution of the factors, either individually or combined, toward limiting worker dose. In this study, worker exposure was predicted using CAM response models developed to evaluate protection levels for continuous and acute releases. Monte Carlo simulations of 10,000 releases were performed using various combinations of model parameter values, with associated uncertainty distributions, to assess the expected ability of a CAM program to meet RPGs, and, further, to assess the relative influence of each factor toward lowering worker exposure. Results showed that improvements to CAM instrument capability combined with better ventilation and CAM placement improve worker protection nonlinearly and that these improvements are critical to meet RPGs. The sensitivity analysis showed that ventilation-driven dilution had the greatest impact on exposure reduction with the selected counting interval for alarm decisions and the alarm set point as secondarily important.

Development and characterization of a wake-controlled exterior hood

A wake-controlled exterior hood was developed to overcome the negative influence of cross draft on an exterior hood and avoid the operation inconvenience caused by the enclosure of an airflow capture booth. This new type of local exterior hood used the hood suction flow to stabilize the dynamic vortex shedding that was induced when a crossflow passed over a blockage plate, and therefore formed a hydrodynamics-stabilized local isolation area for efficient removing of the contaminant. The development process was performed in a test section of an open-circuit wind tunnel. The blockage plate and the exterior hood model were placed in a wind-tunnel test section so that the crossflow could be freely supplied by the airstream of the wind tunnel. The laser light sheet flow visualization method and the laser Doppler velocimeter were employed to reveal the characteristics of the flow field. Primary influential parameters were factored out of the measured velocity results so that a design procedure was proposed. Experiments using hot-wire type alcohol sensors to measure the toluene vapor concentration distributions showed that the capture efficiency of this type of actively controlled hood was remarkably higher than that of an uncontrolled hood.

Estimating personal exposures based on mass balance material usage rates: validation of a ventilation model in a spray paint booth

The goal of this research was to evaluate an estimating model (box model) with direct measurements of contaminants in an industrial spray painting operation. The research involved a dilution ventilation efficiency experiment that was devised to estimate the effective ventilation rate, sampling for organic compounds (xylene, ethyl benzene, methyl ethyl ketone, and methyl isobutyl ketone) in a paint booth, and simultaneously measuring the mass usage of these compounds during painting operations in order to compare measured with predicted concentrations. The results of the dilution ventilation experiment indicated that channeling of air was occurring due to a high ventilation rate in the painting area. The results of the mass balance usage and air sampling comparisons indicated that predicted concentrations were within the 95% upper/lower confidence interval about the geometric mean in 14 out of 16 area samples taken within the paint booth (87.5%). Correlation analysis between predicted concentrations and area, personal, and exhaust stack concentrations were strongest with exhaust (r = 0.923). Correlations with personal concentrations were not as strong (r = 0.828), and the area concentrations were even less strong (0.757). In conclusion, the box model does appear to be a useful additional tool for estimating worker exposures. However, the characteristics of any particular ventilation system must be understood before modeling is conducted.

A quantitative method for optimized placement of continuous air monitors

Alarming continuous air monitors (CAMs) are a critical component for worker protection in facilities that handle large amounts of hazardous materials. In nuclear facilities, continuous air monitors alarm when levels of airborne radioactive materials exceed alarm thresholds, thus prompting workers to exit the room to reduce inhalation exposures. To maintain a high level of worker protection, continuous air monitors are required to detect radioactive aerosol clouds quickly and with good sensitivity. This requires that there are sufficient numbers of continuous air monitors in a room and that they are well positioned. Yet there are no published methodologies to quantitatively determine the optimal number and placement of continuous air monitors in a room. The goal of this study was to develop and test an approach to quantitatively determine optimal number and placement of continuous air monitors in a room. The method we have developed uses tracer aerosol releases (to simulate accidental releases) and the measurement of the temporal and spatial aspects of the dispersion of the tracer aerosol through the room. The aerosol dispersion data is then analyzed to optimize continuous air monitor utilization based on simulated worker exposure. This method was tested in a room within a Department of Energy operated plutonium facility at the Savannah River Site in South Carolina, U.S. Results from this study show that the value of quantitative airflow and aerosol dispersion studies is significant and that worker protection can be significantly improved while balancing the costs associated with CAM programs.

Influence of room geometry and ventilation rate on airflow and aerosol dispersion: implications for worker protection

Knowledge of dispersion rates and patterns of radioactive aerosols and gases through workrooms is critical for understanding human exposure and for developing strategies for worker protection. The dispersion within rooms can be influenced by complex interactions between numerous variables, but especially ventilation design and room furnishings. For this study, dependence of airflow and aerosol dispersion on workroom geometry (furnishings) and ventilation rate were studied in an experimental room that was designed to approximate a plutonium laboratory. Three different configurations of simulated gloveboxes and two ventilation rates (approximately 6 and 12 air exchanges per hour) were studied. A sonic anemometer was used to measure airflow parameters including all three components of air velocity vectors and turbulence intensity distributions at multiple locations and heights. Aerosol dispersion rates and patterns were measured by releasing aerosols multiple times from six different locations. Aerosol particle concentrations resolved in time and space were measured using 16 multiplexed laser particle counters. Comparisons were made of air velocities, turbulence, and aerosol transport across different ventilation rates and room configurations. A strong influence of ventilation rate on aerosol dispersion rates and air velocity was found, and changes in room geometry had significant effects on aerosol dispersion rates and patterns. These results are important with regards to constant evaluation of placement of air sampling equipment, benchmarking numerical models of room airflow, and design of ventilation and room layouts with consideration of worker safety.

Quantitative measurements of airflow inside a nuclear laboratory

Dispersion dynamics of accidentally released radioactive aerosols or gases through laboratory workrooms are determined primarily by airflow, which impacts the level of human exposure and the response of air monitoring instrumentation. Therefore, applying conclusions derived from measurements of the fundamental aspects of airflow (velocity, direction, and turbulence) can lead to better protection of workers by suggesting appropriate locations for air monitoring and sampling. Historically, it has been very difficult to quantitatively measure these fundamental aspects of indoor airflow because of the low flow rates (often <10 cm s(-1)) and difficulties in quantitative measurement of three-dimensional airflow. Recent advances in sonic anemometry have enabled such measurements. For this study, a sonic anemometer was used that was capable of measuring airflow velocities with a sensitivity of about 0.5 cm s(-1) for each of the three-directional components. A sampling frequency of 1 Hz was selected to measure the fluctuations in the air velocity associated with turbulence and expressed in terms of "turbulence intensity." Point measurements of airflow velocities, directions, and turbulence intensities were made at 69 locations in a mechanically ventilated plutonium laboratory located at Los Alamos National Laboratory. Although the measurements were not made with workers present, all measurements were made at a height of 1.5 m, approximately the height of a worker's breathing zone (BZ). Velocities ranged from 8 cm s(-1) to 41 cm s(-1), with a median velocity of 18 cm s(-1). Percent turbulence intensities ranged from 13% to 57% with a median of 34%. The measured velocities and turbulence intensities in the laboratory showed that forced convective flows and turbulent eddy diffusion drive dispersion of released aerosols or gases. Results show that after an airborne release, mixing within the room can take minutes and may not always be complete. This is contrary to simplifying assumptions made by some risk modeling of accidentally released materials in a room. Our results also suggest that the mixing pattern would not be omnidirectional at most release locations, especially in the early stages of the release. Finally, airflow directions were upwards in breathing zones at most workstations. Because most releases in the plutonium laboratory occur at a height immediately below the BZ, the concentrated aerosol could be lifted into the BZ, followed by dispersal to the air monitor with the initiation of alarm.