213
AEROSOLIZATION OF FINE PARTICLES AND ENDOTOXIN FROM METALWORKING FLUIDS
CONTAMINATED WITH MICROORGANISMS.
H. Wang, S. Grinshpun, T. Reponen, University of Cincinnati, Cincinnati, OH.
Metalworking fluid (MWF) exposures have been associated with adverse health effects, such as dermatitis, respiratory symptoms, asthma, and in some cases hypersensitivity pneumonitis. No sufficient information has yet been collected on the size distribution of particles aerosolized from MWFs contaminated with microorganisms and airborne endotoxin concentration. We have recently developed a laboratory-scale setup, which simulates grinding operations in the MWF industry. Our preliminary study with this simulator showed increased aerosolization of fine particles from semisynthetic MWF after the fluid was inoculated with Pseudomonas fluorescens under laboratory-controlled conditions. In the present study, we investigated the aerosolization of fine particles and endotoxin from two types of water-soluble MWFs—semisynthetic MWF and soluble oil—after the fluids were inoculated with P. fluorescens in the laboratory. The simulator was also utilized to test used fluids that were brought from the field sites. The concentration of fine particles was measured using a condensation nucleus counter (P-track, model 8525, TSI Inc.). Particle size distributions and collection of particles for endotoxin analysis were performed by an electrical low-pressure impactor (ELPI; 3935 series, Dekati Ltd., Tampere, Finland). The endotoxin analysis was performed with limulus amoebocyte lysate assay. It was found that after bacterial inoculation, semisynthetic MWF had a greater increase of fine particle aerosolization than soluble oil. The peak of the fine particles aerosolized from used MWFs (aerodynamic diameter, da = 0.029 µm) and that from MWFs inoculated with bacteria (da = 0.037 µm) were smaller than that of pure bacterial water suspension. Particles at the size smaller than intact bacterial cells contained significant concentration of endotoxin. This indicates that some of the fine particles may come from the cell wall fragments of the bacteria in the MWFs.
214
MIST GENERATION FROM VEGETABLE OIL-BASED METALWORKING FLUIDS BY THREE
MECHANISMS.
S. Kim, P. Raynor, University of Minnesota, Minneapolis, MN.
Vegetable oil-based metalworking fluids (MWFs)
may pose fewer health concerns and reduce disposal costs relative to traditional
MWFs made using petroleum-based oils. Mist generation by the impaction,
centrifugal force, and evaporation/recondensation mechanisms for several
experimental vegetable oil-based MWF formulations was measured. The amount of
mist formation was compared to generation with a traditional petroleum-based
soluble oil. The mist generated by a lathe-mimicking apparatus traveled through
a wind tunnel and was sampled by a real-time particle counting and sizing
instrument. Five experimental emulsions were formulated and tested with one
commercial petroleum-based formulation and one commercial vegetable oil-based
formulation. The vegetable oil-based emulsions produced about the same quantity
of particles by impaction as the petroleum-based emulsion, except for the
air-oxidized experimental fluid. Most of the vegetable oil-based fluids
generated more droplets by centrifugal force than the soluble oil. However, the
numbers of droplets measured for the air-oxidized soybean oil were generally not
different statistically from the quantity of mist observed using the soluble
oil. Although the commercial vegetable oil-based emulsion demonstrated about the
same amount of mist generation as the soluble oil in the evaporation/recondensation
tests, the experimental fluids generally exhibited between 30 and 90% less mist
formation than the soluble oil. The experimental fluid that performed best in
these experiments was the air-oxidized modified soybean oil. Actual machining
tests with this fluid are necessary to verify reductions in mist
generation.
215
AIRBORNE RESPIRABLE CRYSTALLINE SILICA FROM FLY ASH AT COAL FIRED POWER PLANTS.
J. Hicks, Exponent Inc., Oakland, CA; J. Yager, EPRI, Palo Alto, CA.
Coal fly ash is the primary solid waste generated from coal combustion. Workers at coal fired power plants may encounter this fine powered ash material during day to day handling of the solid waste, and during maintenance activities, especially during routine outages when interior chambers of the boiler and ash removal equipment are entered by work crews. Much of the ash is in the respirable size range, and may easily become airborne. In interior chambers of the boiler and associated structures, ventilation is often limited, and airborne ash is readily noticeable. This ash contains detectable levels of crystalline silica, in the form of alpha quartz, representing a potential silicosis hazard. This study presents the results of breathing-zone respirable air sampling and analysis for quartz during both nonmaintenance and maintenance activities at six coal fired power plants that utilized different types of coal. This work was conducted as part of a large coal fly ash exposure assessment, in which the field work was completed approximately 10 years ago. The coal types studied included western sub-bituminous, interior and eastern bituminous, and lignite, all mined domestically in the United States. Workers engaged in a wide cross-section of normal activities were sampled over their full work-shifts to determine airborne concentrations of respirable crystalline silica. Air samples were collected using standard miniature cyclones as the pre-selection dust sampling device, and the collected dust samples were analyzed by gravimetric and X-ray diffraction methods. The air sampling and analytical results are compared to current and proposed occupational health exposure limits. The results revealed that a significant fraction of the maintenance-related work activities, and a smaller fraction of the nonmaintenance activities, had time-weighted average airborne concentrations above the current and proposed TLVs or PELs, indicating the need for appropriate exposure control procedures.
216
CHROMIUM PARTICLE SIZE DISTRIBUTION AND SPECIATION IN PAINT SPRAY AEROSOL: A
FIELD STUDY.
R. Sabty-Daily, California State University–Los Angeles, Los Angeles, CA; P. Harris, W. Hinds, J. Froines, University of California–Los Angeles, Los Angeles, CA.
Spray painting of chromate-containing paint represents a potential source of occupational exposure to Cr(VI) in the aerospace industry. Two field studies were conducted to determine the size distribution and speciation of Cr in chromate-based paint spray aerosol. Sampled paint consisted of strontium chromate in an epoxy resin matrix. Personal aerosol samples were collected using Sierra Marple cascade impactors and analyzed for Cr(VI) and total Cr. Size distributions of total Cr and Cr(VI) particles had a mass median aerodynamic diameter of 7.5 µm (GSD = 2.7 µm) and 8.5 µm (GSD = 2.2 µm), respectively. Particles larger than 2 µm were log normally distributed and constituted greater than or equal to 90% of the total Cr and the Cr(VI) mass in all sampled aerosols. The target respiratory deposition site of Cr was estimated based on Cr mass distribution according to particle size. On average, 62% of the Cr and Cr(VI) mass in the paint aerosol consisted of particles > 10 µm. Results showed 71.8% of Cr(VI) mass in paint spray aerosol potentially inhaled by a spray painter may deposit in the head airways region. Only less than or equal to 2.0% of Cr(VI) mass may potentially deposit in each of the alveolar and tracheobronchial regions. Cr(VI) mass to total Cr mass ratio was determined in bulk paint; the data indicate Cr was predominantly in the Cr(VI) state, before spraying. The same ratio was determined in paint aerosol samples. Results showed there was reduction of Cr(VI) regardless of Cr aerosol particle size. Cr(VI) reduction most likely occurred during the eight-hour sample collection time period. These findings are in agreement with findings of others that observed Cr(VI) reduction during collection of airborne Cr(VI) in samples of chromic acid mist. Use of Cr(VI) stabilizing sampling media and storage of samples at lower temperatures (4°C ) during and after sampling may avoid the underestimation of Cr(VI).
217
ON-SITE METHODS FOR ASSESSMENT OF AEROSOL AND METAL EXPOSURE.
O. Nygren, National Institute for Working Life, Umeĺ, Sweden.
Traditional assessment of occupational exposure to aerosols and metals involves a two-step procedure with filter sampling at the workplace followed by analysis of the samples in a laboratory. After a gravimetric determination of the aerosol content on the filter, determination of metals is carried out using atom spectrometric methods (e.g., AAS, ICP-AES, ICP-MS, XRF). This technique gives results with high accuracy and low detection limits. However, the technique has a significant drawback. Since the samples have to be analysed in a laboratory, the results will be obtained days or weeks after the sampling occasion.
Today a new generation of portable instruments is available. These instruments will make on-site measurements of aerosol and metal exposure possible, which opens for new strategies for assessment of occupational exposure, as complements to traditional monitoring. In combination with portable high-flow pumps, short-term sampling is possible, which allows monitoring the exposure variation during a work shift, as well as the exposure during individual work tasks with short duration. Screening measurements and emission measurements are other examples of monitoring that are facilitated using on-site determinations. Control of various measures can be performed on site and will be an effective tool for assessment of workplace improvements. On-site determinations can also be an effective and pedagogic tool to demonstrate to the workers how specific work tasks can be performed to minimize the exposure, as well as the effectiveness of different measures made to improve their work environment.
Methods for sampling aerosols on filters and collecting wipe samples of deposited aerosols will be presented. The aerosols on filter samples are determined by gravimetry followed by determination of metals using a portable XRF. The metals sampled on wipe samples are also determined using a portable XRF. Validation data and examples of strategies will be presented with real data from on-site measurements.
218
DEVELOPMENT OF A CFD MODEL FOR PARTICLE INHALABILITY STUDIES.
T. Anthony, M. Flynn, University of North Carolina, Chapel Hill, NC.
Currently, the inhalable particulate mass curve does not address aspiration efficiency at low velocity conditions typical of indoor work environments. Traditional methods for investigating large particle inhalability using breathing mannequins in wind tunnels require uniform freestream particle concentrations, which are difficult to maintain at indoor air velocities (0.3 m/s). Simulations using computational fluid dynamic (CFD) methods provide an alternative method to investigate inhalability. CFD simulations can minimize the uncertainty surrounding the freestream particle concentration, providing more confidence in the determination of aspiration efficiencies. In this work, a three-dimensional computational fluid flow model is developed and validated for an inhaling mannequin with realistic facial features in a low velocity environment. Turbulence was simulated using the standard k-e model. Evaluation of the fluid flow model was conducted to ensure the models’ convergence and to determine the simulation uncertainty. The model was then validated with data from laser Doppler anemometry measurements in a low velocity wind tunnel with a similarly dimensioned inhaling anatomical mannequin. The developed CFD model based on k-e equations at iterative tolerances of 1E-5 showed sufficient agreement with the velocity measurements and is suitable for subsequent aerosol inhalability simulations for the investigation of particle inhalability. This paper will present the model, discuss the uncertainty associated with the velocity and turbulence fields, and detail the computational cost of this three-dimensional model.
219
TECHNIQUE IMPROVEMENT FOR REDUCING PARTICLE BOUNCE AND LOADING EFFECT OF
MULTI-HOLE IMPACTOR.
C. Lai, C. Lin, C. Chiang, Chung Shan Medical University, Taichung, Taiwan Republic of China; C. Chen, National Taiwan University, Taipei, Taiwan Republic of China.
The goal of aerosol sampling is to evaluate the health hazard caused by the deposited particles in the human breathing system. Therefore, aerosol must enter the sampler and be deposited on the collection medium without loss. Impactors, widely used aerosol samplers, are found the reduction of impaction efficiency due to particle bounce. Moreover, long-term sampling may significantly affect particle collection. The sampler cannot provide accurate sampling under these circumstances. Particle bounce from an impaction surface depends on many parameters. The characteristics of the impaction surface also play an important role. To prevent particle bounce, the impaction plate is usually coated with oil or grease. However, these coating materials were found that cannot sustain long-term particle loading. In the study, the researchers tried to solve these problems by using an agar collection surface. An ultrasonic atomizing nozzle was used to generate challenge aerosols (potassium sodium tartrate tetrahydrate, PST). The mass concentration of challenge aerosol was about 20 mg/m3, in order to show the worst case. A 25-m Ci radioactive source, Am241, was used to neutralize the challenge particles to the Boltzmann charge equilibrium. An aerodynamic particle sizer was used to measure the number of concentrations and size distributions upstream and downstream of the size-selective devices. The oil, grease, and Tryptone Soy Agar coating was compared respectively for the preventing of solid particle bounce. A multi-hole impactor and personal environmental monitor (PEM) were used to evaluate the particle bounce and loading effect. The results showed the solid PST particles bounced less off the agar-coating plate than silicone oil and grease-coating plates. However, the coated agar shrunk after two hours of sampling. Finally, the study used oil-agar coating and successfully overcame not only the particle bounce but also the loading effect. The results also showed the oil-agar coating could be applied to PEM impactors.
220
A COMPARISON OF THE COLLECTION EFFICIENCY CURVES OF FOUR DIFFERENT PERSONAL
SAMPLERS.
V. Golla, P. O’Shaughnessy, The University of Iowa, Iowa City, IA.
The collection efficiencies of four personal aerosol samplers, the IOM, Button, 3-piece cassette, and aluminum cyclone, were assessed through trials conducted in an environmental chamber under low-flow conditions. The samplers were attached to sampler holding devices (SHDs) designed to allow particles penetrating the sampler inlet to flow directly into a particle counter. Two counters were used for each trial; one to compensate for the time-varying nature of the dust concentrations, and the other with the SHD alternately attached and detached at 15-minute intervals. The counters measured particles in 12 size channels between 0.4 and 15 microns. The particle counter flow rate was 1.2 L/min; therefore, additional air was also drawn via a vacuum pump connected to the SHDs to maintain the correct sampler flow rates which varied between 2.0 and 4.0 L/min. A form was used to mimic a human torso and hold the sampling devices in their proper orientation relative to that worn during personal sampling. Both an inorganic (Arizona Road Dust (ARD)) and organic dust (pulverized grain dust (GD)) were analyzed. After correcting for time variations, collection efficiency was computed from the counts in each channel when the SHD was attached relative to when it was detached. Results indicated that the IOM and Button efficiency curves were higher than the inhalable curve for all particle sizes and dust types whereas the cassette sampler was lower. For the cyclone, the collection efficiency curve resulted in a smaller cut-diameter than that indicated by the respirable curve (4 microns). Differences were seen in the curves when sampling ARD versus GD suggesting a particle shape factor influences sampler efficiency.
221
EVALUATION OF 3M FILTRETE ELECTROSTATIC FILTER FOR SAMPLING AND ANALYSIS OF
OCCUPATIONAL EXPOSURE TO AEROSOLS.
J. Dennis, M. Abdel-Salam, University of Bradford, Bradford, United Kingdom.
Occupational hygiene routinely requires the use of filters to collect aerosol for gravimetric and subsequent analysis. The technique of drawing pumped through the filter has changed little since its adoption with cellulose filters in the 1950s. We have evaluated a new electrostatic aerosol collection medium commonly used in disposable respirators, namely the 3M Filtrete product at 150 g/m3 density weight. We have evaluated its properties as a useful low resistance alternative to conventional GF/A and membrane filters. Results show no significant weight instability, and no discernable chemical interference or limitations to the use of Filtret in the collection and analysis of aerosol residue by solvent or acid desorbtion. The 100-fold lower resistance (0.1 vs 10 inches wg) of the Filtrete compared to traditional membrane or GF/A media offers potential to develop a fan-based aerosol sampler to replace traditional diaphragm pumps. Fan-based systems would offer considerable advantages in weight, size, and operational noise which, in turn, would facilitate more discrete sampling and allow collection of a sample more representative of true occupational exposure. We conclude that collection and analysis characteristics of the 3M Filtrete are appropriate as a sampling medium in occupational hygiene.
Posted May 30, 2005