Biomedical subjects

J J Whicker

Publications and source records attributed to J J Whicker.

4 recordsLinked to original sources

PubMed2000

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.

Air Pollution, Radioactive↗

PubMed1999

Assessment of need for transport tubes when continuously monitoring for radioactive aerosols.

Aerosol transport tubes are often used to draw aerosol from desirable sampling locations to nearby air sampling equipment that cannot be placed at that location. In many plutonium laboratories at Los Alamos National Laboratory, aerosol transport tubes are used to transport aerosol from the front of room ventilation exhaust registers to continuous air monitors (CAMs) that are mounted on nearby walls. Transport tubes are used because past guidance suggests that extraction of aerosol samples from exhaust locations provides the most sensitive and reliable detection under conditions where the rooms have unpredictable release locations and significant spatial variability in aerosol concentrations after releases, and where CAMs cannot be located in front of exhaust registers without blocking worker walkways. Despite designs to minimize particle loss in tubes, aerosol transport model predictions suggest losses occur lowering the sensitivity of CAMs to accidentally released plutonium aerosol. The goal of this study was to test the hypotheses that the reliability, speed, and sensitivity of aerosol detection would be equal whether the sample was extracted from the front of the exhaust register or from the wall location of CAMs. Polydisperse oil aerosols were released from multiple locations in two plutonium laboratories to simulate plutonium aerosol releases. Networked laser particle counters (LPCs) were positioned to simultaneously measure time-resolved aerosol concentrations at each exhaust register (representative of sampling with transport tubes) and at each wall-mounted CAM location (representative of sampling without transport tubes). Results showed no significant differences in detection reliability, speed, or sensitivity for LPCs positioned at exhaust locations when compared to LPCs positioned at the CAM wall location. Therefore, elimination of transport tubes would likely improve CAM performance.

Aerosols↗

PubMed1999

Room airflow studies using sonic anemometry.

To ensure prompt response by real-time air monitors to an accidental release of toxic aerosols in a workplace, safety professionals should understand airflow patterns. This understanding can be achieved with validated computational fluid dynamics (CFD) computer simulations, or with experimental techniques, such as measurements with smoke, neutrally buoyant markers, trace gases, or trace aerosol particles. As a supplementary technique to quantify airflows, the use of a state-of-the art, three-dimensional sonic anemometer was explored. This instrument allows for the precise measurements of the air-velocity vector components in the range of a few centimeters per second, which is common in many indoor work environments. Measurements of air velocities and directions at selected locations were made for the purpose of providing data for characterizing fundamental aspects of indoor air movement in two ventilated rooms and for comparison to CFD model predictions. One room was a mockup of a plutonium workroom, and the other was an actual functioning plutonium workroom. In the mockup room, air-velocity vector components were measured at 19 locations at three heights (60, 120 and 180 cm) with average velocities varying from 1.4 cm s-1 to 9.7 cm s-1. There were complex flow patterns observed with turbulence intensities from 39% up to 108%. In the plutonium workroom, measurements were made at the breathing-zone height, recording average velocities ranging from 9.9 cm s-1 to 35.5 cm s-1 with turbulence intensities from 33% to 108%.

Aerosols↗

PubMed1997

Evaluation of continuous air monitor placement in a plutonium facility.

Department of Energy appraisers found continuous air monitors at Department of Energy plutonium facilities alarmed less than 30% of the time when integrated room plutonium air concentrations exceeded 500 DAC-hours. Without other interventions, this alarm percentage suggests the possibility that workers could be exposed to high airborne concentrations without continuous air monitor alarms. Past research has shown that placement of continuous air monitors is a critical component in rapid and reliable detection of airborne releases. At Los Alamos National Laboratory and many other Department of Energy plutonium facilities, continuous air monitors have been primarily placed at ventilation exhaust points. The purpose of this study was to evaluate and compare the effectiveness of exhaust register placement of workplace continuous air monitors with other sampling locations. Polydisperse oil aerosols were released from multiple locations in two plutonium laboratories at Los Alamos National Laboratory. An array of laser particle counters positioned in the rooms measured time-resolved aerosol dispersion. Results showed alternative placement of air samplers generally resulted in aerosol detection that was faster, often more sensitive, and equally reliable compared with samplers at exhaust registers.

Aerosols↗