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Biomedical subjects

K Willeke

Publications and source records attributed to K Willeke.

At least 55 records · Page 3Linked to original sources
PubMed1987

Respirable dust control in grinding gray iron castings.

High speed grinding of gray iron castings long has been associated with excessive exposure to crystalline silica. Not all workers engaged in these operations are protected by conventional ventilation techniques. Dust in the air that has been entrained by the spinning grinding wheel and not captured in the grinder hood has been postulated to be a major exposure source. A pilot grinding operation was constructed, and the size distribution and concentration of airborne particles were measured with the aerodynamic particle sizer (APS). Various control measures proved effective in reducing the respirable dust concentration: increased exhaust ventilation, and installation of baffles and/or the use of an air jet to deflect the entrained air stream. The concentration of respirable dust is the breathing zone was reduced approximately 20-fold through the combined use of increased ventilation, interior baffles, and an air jet. The air jet and baffle utilized at the base ventilation rate reduced the respirable dust concentration by a factor of three to four, whereas the baffle alone halved the concentration.

Air Pollutants, Occupational↗
PubMed1987

Particle size-dependent leakage and losses of aerosols in respirators.

Measuring particle size-dependent leakage into and losses inside a respirator reveals the deposition mechanisms occurring at the leak site and the flow dynamics inside the respirator. This study investigated particle size-dependent leakage and deposition within the mask by examining the leakage into the mask for different hole locations, probe locations, hole shapes, hole lengths and hole sizes. The shape of the leak has an effect on particle size-dependent leakage. Probe and leak location tests indicated that not only does the total measured leakage change but also the size-dependence of the leakage changes depending on the leak and probe locations. When the leak site is in the chin area, the clean air entering through the filters at the chin helps to carry the inward leakage into the breathing zone. Particle size-dependent leakage does occur and is due to both inertial entry losses at the leak site and within the mask, and diffusional losses within the mask and leak site. Particle size-dependent curves change shape as the hole size changes with relatively more larger particles entering through the small hole size.

Aerosols↗
PubMed1987

The effect of aerosol size distribution and measurement method on respirator fit.

The particle size-dependent leakage into a respirator was examined by measuring the leakage of particle sizes between 0.07 to 4.4 microns through three hole sizes in a negative-pressure half-mask respirator worn by a human subject. This investigation showed that the size distribution of an aerosol test agent and the measurement method have an effect on the leakage measured in a quantitative fit test. For instance, the ratio of percent leakage measured by light scattering between test aerosols with count median diameters of 2.2 and 0.28 microns can be as large at 5:1. Likewise, the ratio of the percent leakage measured by a particle count method vs. a mass method of detection of the same polydisperse aerosol with a count median diameter equal to 2.2 microns can be as high as 4:1. The mass leakage into a mask with a leak is also greater for an exposure aerosol with a count median diameter between 0.15 to 0.30 micron compared to exposure aerosols with larger count median diameters for aerosols with the same mass concentration.

Aerosols↗
PubMed1986

Respirable droplets from whirlpools: measurements of size distribution and estimation of disease potential.

Droplets generated from water surfaces have been implicated in a number of diseases such as Legionnaires' disease and Pontiac fever. These droplets can be inhaled by people and can deposit in the respiratory system. The physical size of the droplets is critical in determining whether the droplets can contain the bacteria, reach the breathing zone of the subject, and deposit in the respiratory tract. The present study establishes the presence of water droplets above the surface of health club whirlpools. These droplets are of the appropriate size for causing respiratory disease. Several factors including pool temperature, bubbling action during operation, and height above the water surface have been investigated. The results are related to the deposition of the droplets, and hence bacteria, in the various regions of the respiratory tract.

Aerosols↗
PubMed1986

Size and concentration measurement of an industrial aerosol.

Several real-time particle sizing instruments were evaluated for measuring the size distribution and concentration of the aerosol produced during the high speed grinding of gray iron castings. Aerosol was sampled in the airstream entrained by the motion of a spinning grinding wheel in a pilot grinding operation. Measurement methods based on differing physical principles were selected for evaluation and compared: particle inertia (aerodynamic particle sizer and quartz crystal microbalance cascade impactor); light scattering (laser aerosol spectrometer); and projected-area microscopy (scanning electron microscope). Inferences of aerodynamic diameter based on measurements by the laser aerosol spectrometer consistently undersized that determined by the aerodynamic particle sizer by a factor of 1.5. Estimates of aerodynamic diameters from projected area diameters determined by scanning electron microscopy differed from those obtained by the aerodynamic particle sizer by a factor of 2. Differences appeared to be a non-linear function of particle diameter. Estimates of respirable mass determined from mass-weighted particle size spectra varied by a factor of 6 between the largest estimate (scanning electron microscope) and the smallest estimate (laser aerosol spectrometer).

Aerosols↗
PubMed1984

Size classification of fibers and isometric particles keeping each fraction airborne.

The hazardous properties of airborne fibers are generally thought to be related to size. The purpose of this study was to develop a technique for physically classifying airborne fibers on the basis of diameter, keeping the separated fractions in the suspended state. This would permit either fraction to be further classified, monitored by real-time instrumentation and/or used in size-related inhalation studies. Other fiber classification methods have involved deposition of fibers onto a substrate, which precludes these advantages. Diameter classification was achieved by the use of an opposing-jet aerosol classifier. With isometric aerosols, sharp diameter classification was achieved: D50/D16 = 1.1 for liquid particles, and D50/D16 = 1.3 for solid particles. Diameter classification of fibers was also achieved, but the sharpness of cut was much less; D50/D16 greater than 3. The decreased sharpness of cut for fibers is attributed to the more or less random bounce of fibers from the edge of the separation plate to either outlet flow of the classifier. The sharpness of cut is expected to be better in a classifier in which the thickness of the separation plate is smaller relative to the flow dimensions.

Aerosols↗
PubMed1984

Total deposition of ultrafine sodium chloride particles in human lungs.

The total deposition of monodisperse, 0.026-0.19 micron (dry volume equivalent diameter) sodium chloride particles in the lungs of five healthy subjects, who breathed orally, was measured. For a tidal volume of 1,000 ml and flow rate of 500 ml/s, the percentages deposited were: 37.2 +/- 8.4% (mean +/- SD) for 0.026 micron, 23.8 +/- 3.3% for 0.051 micron, 22.8 +/- 3.1% for 0.096 micron, and 31.8 +/- 6.2% for 0.19 micron particles. The deposition minimum corresponded to a particle size of approximately 0.08 micron. Deposition did not correlate with measures of lung volume or body size but did correlate with forced expired flow rate after 75% of forced vital capacity (FVC) exhaled (FEF 75%/FVC) and with percent-predicted values for FEF 25-75% and FEF 75%. Lengthening the breathing period from 4 to 8 s/breath while maintaining flow rate at 500 ml/s caused an additional 11.3 +/- 3.1% of the inhaled particles to deposit. Sedimentation and diffusion were found to be the principal deposition mechanisms. These hygroscopic particles deposited according to sizes they would attain in air with a relative humidity between 96 and 100%.

Adult↗
PubMed1978

Variable-cut particle-size classification by opposing jets.

A new technique of aerodynamic particle-size classification has been developed utilizing axisymmetrically-opposed air jets. For a fixed geometry the cut size can be varied from 0.8 to 3.6 micrometer by changing the jet flow rates. Future designs are expected to extend the useful particle-size range. Particles remain airborne after size separation, permitting the use of continuous, automated methods for analyzing the particle concentration and chemical compositon.

Air Pollutants↗
PubMed1975

Performance of the slotted impactor.

Slotted impactors perform with a sharpness of cut close to the theoretically predicted value, if used under the conditions of the numerical model. Sideways flow entrance and impaction onto a fibrous surface may change the collection efficiency considerably.

Aerosols↗
PubMedDate not supplied

Performance characteristics of the button personal inhalable aerosol sampler.

The button inhalable aerosol sampler with a curved porous inlet recently was developed and evaluated as a stationary sampler in the laboratory and in the field. The present study focused on investigating its suitability for personal inhalable aerosol sampling. The button sampler was tested at two wind velocities (0.5 and 2.0 m/sec), three particle sizes (7, 29, and 70 microm) and three orientations to the wind (0, 90, and 180 degrees). The performance characteristics of the button sampler were compared with those of three other personal samplers--the IOM (Institute of Occupational Medicine), GSP, and 37-mm closed-face filter cassette. The experiments were conducted in a wind tunnel with the samplers mounted on a full-size manikin. The direction-specific sampling efficiency of the button sampler was found to be essentially independent of the wind direction and dependent on the wind velocity to a much smaller degree than that of the three other samplers. When direction-averaged, the fit of its sampling efficiency curve to the inhalability curve was found to be better than that of the 37-mm closed-face cassette, comparable with that of the GSP sampler, and less than that of the IOM sampler. The precision of the button sampler was found to be generally equal to or better than the precision of the comparison samplers. It was concluded that the button sampler can be successfully used as a personal inhalable aerosol sampler.

Aerosols↗
PubMedDate not supplied

Release of lead-containing particles from a wall enclosure.

The 1995 Department of Housing and Urban Development (HUD) Guidelines for the Evaluation and Control of Lead-Based Paint Hazards in Housing discusses using interior and exterior wall enclosures for lead hazard control. Leaded dust may be aerosolized inside enclosures and released through gaps and cracks into a room. The effects of airflow and mechanical disturbances on dust release were studied using a laboratory wall enclosure model with dust collected from homes with lead-based paint hazards. Airflows relevant to residences were blown down the enclosure and out a 4-, 6-, or 8-mm horizontal gap at its bottom, simulating potential enclosure failure. Then, low-frequency mechanical vibrations also were applied to the enclosure. No significant dust release was found when blowing air down the enclosure even at 37 cm/sec (representing extremely high flow); release occurred only with this high flow and 3 Hz mechanical disturbances. Dust was released primarily from the floor area immediately adjacent to the enclosure gap; the release rate fluctuated over time. Most dust initially settled near the enclosure. Dust release for 1 hour at extreme conditions (high airflow with vibration) yields lead loading above the 1995 HUD clearance level of 100 microg/ft2 only within 3-4 cm of the wall; for the HUD standard (1 ft2) sampling area, the lead loading does not exceed 30 microg/ ft2. Redistributing dust over the room's 16 m2 floor space yields average extreme-condition loading rate of 2 microg/ft2/hour. At less-than-extreme conditions, dust would have to be released for years without cleaning to yield a hazard.

Dust↗
PubMedDate not supplied

Particle settling after lead-based paint abatement work and clearance waiting period.

This study investigated the evolution of airborne particle concentration and size distribution following abatement work in a controlled environment utilizing direct real-time particle monitoring and used it to project potential lead loadings as those particles settle. An 860 ft3 environmental test chamber with sophisticated ventilation and air purifying systems was built. Wooden doors with lead-based paint were dry sanded or scraped to generate the highest feasible airborne lead concentrations. Size-fractional airborne particle concentrations decreased exponentially with time in all tests, even with no air exchange, consistent with the stirred model of constantly mixed air, which predicts longer settling than for tranquil settling. Very low levels of air mixing generated by temperature gradients and initial room air turbulence affected particle settling. About 90% of airborne lead mass settled within 1 hour after active abatement, before final cleaning began. During the second waiting period of 1 hour, which followed cleaning of the floor, additional dust settled so that the additional potential lead loading from remaining airborne lead was less than 20 microg/ft2. For this worst case scenario, the underestimate of the lead loading done by the clearance sampling did not exceed about 30%. For more realistic conditions, the underestimates are projected to be much lower than the new 40 microg/ft2 Housing and Urban Development (HUD) clearance standards for floor dust lead. These results were obtained for the first waiting period (between the end of active abatement and the beginning of cleaning) of 1 hour, as recommended by HUD guidelines. Thus, this study demonstrates no need to increase either the first or second waiting period.

Air Pollutants, Occupational↗
PubMedDate not supplied

Performance of Air-O-Cell, Burkard, and Button Samplers for total enumeration of airborne spores.

Performance of three devices used for the total enumeration of airborne spores-the Air-O-Cell sampling cassette, the Burkard personal volumetric air sampler, and the Button Aerosol Sampler--was evaluated under controlled laboratory conditions. The first two are glass-slide impactors; the third collects spores on a filter. The samplers were challenged with 0.44-5.10 microm polystyrene latex particles and five microorganisms of 0.84-3.07 microm mean aerodynamic diameter: Streptomyces albus, Bacillus subtilis, Cladosporium cladosporioides, Penicillium brevicompactum, and Penicillium melinii. An optical particle counter measured the particle concentrations upstream and downstream of each sampler, and thus determined the physical collection efficiency of the three samplers. Collection efficiency of the Button Aerosol Sampler was close to 100% for the entire particle size range studied. The cut-off size of each impactor was 2.3-2.4 microm. Acridine orange (with epifluorescent microscopy) and lactophenol cotton blue (with bright light microscopy) staining techniques were used for the microscopic enumeration of spores. No significant difference in microscopic counts was found (at the 95% significance level) when using these two techniques with the Button Aerosol Sampler filters. When the lactophenol cotton blue staining was used to compare total microbial counts yielded by all three samplers, the Button Sampler showed significantly higher counts for the smaller size microorganisms (B. subtilis and C. cladosporioides). For the larger microorganisms (P. brevicompactum and P. melinii) all three samplers yielded similar results. Uniformity of particle deposition on the collection surface was highest for the Button Aerosol Sampler due to the design of its inlet. Thus, the filter collection method used with the Button Aerosol Sampler is suitable and can be advantageous for the enumeration of total airborne spores.

Aerosols↗
PubMedDate not supplied

Test methods for evaluating the filtration and particulate emission characteristics of vacuum cleaners.

The overall filtration efficiency of a vacuum cleaner traditionally has been tested by placing the vacuum cleaner in a test chamber and measuring aerosol concentrations at the chamber inlet and outlet. The chamber test method was refined and validated in this study. However, this chamber test method shows an overall filtration efficiency of close to 100% for most of the industrial vacuum cleaners and for most of the newly developed household vacuum cleaners of midprice range or higher because all these vacuum cleaners have a high-efficiency particulate air (HEPA) or other highly efficient filter installed at the exhaust. A new test method was therefore developed through which the vacuum cleaner was probed in various internal locations so that the collection efficiency of the individual components could be determined. For example, the aerosol concentration upstream of the final HEPA filter can thus be measured, which permits one to estimate the life expectancy of this expensive component. The probed testing method is particularly suitable for field evaluations of vacuum cleaners because it uses compact, battery-operated optical particle size spectrometers with internal data storage. Both chamber and probed tests gave the same results for the aerosol filtration efficiency. The probed testing method, however, also gives information on the performance of the individual components in a vacuum cleaner. It also can be used to determine the dust pickup efficiency and the degree of reaerosolization of particles collected in the vacuum cleaner.

Air Pollution, Indoor↗