Advances in Aerosol Technology

PO1​20

Wednesday, May 25, 2016, 1:30 PM - 4:30 PM

SR​-120-01

Aerosol and Volatile Organic Compounds Emissions from a Low-Cost 3-D Printer

J. Wang, E. Floyd, and J. Regens, Occupational & Environmental Health, University of Oklahoma Health Sciences Center, Oklahoma City, OK

Objective: 3-D printing is an additive manufacturing process involving injection of melted thermoplastic polymers which are then laid down in layers to achieve a predesigned shape. The heated deposition process raises concern of potential aerosol and volatile organic compounds (VOCs) emission and exposure. The lowered cost of desktop 3-D printers brought more applications to places where sufficient ventilation is often lacking. Meanwhile, little is known about characteristics of 3-D printing fume. The objective of this study was to characterize the aerosol and VOCs generated from a low cost 3-D printer with various filaments in an environmental testing chamber.

Methods: A predesigned object was printed in 1.25 hours using eight types of filaments. A scanning mobility particle sizer and aerodynamic particle sizer were employed to measure the particle size distribution in the fine (<0.5 µm) and coarse ranges (0.5~20 µm). Real-time VOCs concentration was monitored by a photoionization sensor and sampled on a thermal desorption tube and analyzed by thermal desorption gas chromatography mass spectrometry.

Results: The results showed a high number (7.4×109 to 3.2×1010 #/min) of ultrafine particles (41.4~83.0 nm) were found in the fume. VOC emission rates were between 20.4 to 30.6 µg/min, with predominant VOC species from breakdown and reaction products of the filaments, such as styrene for ABS-based filament and acrylic acid dimer for PLA-based filament.

Conclusions: The findings suggest that although the VOC concentrations were much lower than occupational exposure limits, ultrafine particles could still lead to health risks for low cost 3-D printer users.

 

SR-120-​02

Estimation of Airborne Diesel Particulate Matter Concentrations Using Real-Time Aerosol Monitoring Instruments

L. Pahler and R. Larson, University of Utah, Salt Lake City, UT

Objective: Currently, there are limited real-time monitoring methods for estimating airborne diesel particulate matter (DPM) concentrations in the mining industry. This study investigated whether a Grimm 1.109 Aerosol Spectrometer, a Hazdust EPAM 5000, and a DustTrak 8520 could be used to estimate airborne DPM concentrations in hard rock mines when compared to SKC DPM cassette sampler results.

Methods: The objective of this study was accomplished by determining the correlation of DPM concentrations provided by GS-1 Cyclone - SKC DPM cassette samplers to simultaneously collected Grimm, HazDust, and DustTrak aerosol spectrometer particulate concentrations. Seven DPM sampling events resulted in the collection of 42 SKC DPM cassette samples following NIOSH Method 5040 sampling procedures and 7 blank SKC DPM cassette samples. The SKC DPM cassette sampler DPM concentrations were determined following NIOSH method 5040 analytical procedures. Linear regression equations were generated by comparing DPM concentrations collected by SKC DPM cassette samplers and particulate concentrations measured by the Grimm, Hazdust, and DustTrak aerosol instruments.

Results: Statistical results of the linear regression analysis of the Grimm, Hazdust, and DustTrak aerosol instrument concentration data and SKC DPM sampler concentration data obtained during seven sampling events (N=42) show a strong relationship between the aerosol instrument data and SKC DPM cassette data: R2=0.86, p=0.002 (Grimm); R2=0.96, p=0.01 (Hazdust); and R2=0.97, p<0.001 (DustTrak).

Conclusions: Results of this study demonstrate that a strong correlation exists between Grimm, Hazdust, and DustTrak aerosol instrument data and SKC DPM cassette sample data for airborne DPM concentrations when sampling was carried out in hard rock mines.

 

SR-12​0-03

Performance Testing of a Handheld Nebulizer

T. Yang, N. Yu, S. Huang, and C. Chen, Department of Public Health, National Taiwan University, Taipei, Taiwan; Y. Kuo, Chung Hwa University of Medical Technology, Tainan, Taiwan

Objective: Vibrating mesh aerosol generators have been reported to have increased output efficiency, minimal residual volume, and high percentage of particles in the emitted respirable and fine particle fraction. This work aimed to thoroughly characterize a miniaturized vibrating mesh nebulizer, uniquely applying capillary force for solution delivery.

Methods: The miniaturized vibrating mesh aerosol nebulizer tested in this work consisted of a nebulization unit, a liquid reservoir and transport device. One AAA battery was used to power the nebulizer, in order to miniaturize the device and operate for long hours. The vibrating mesh plate was placed on top of the solution transport device which was composed of two circular tubes, designed to deliver solution by capillary force. The aperture size of vibrating mesh plate was 15 μm. There were 2375 tapered holes on the mesh and the aperture distance was 160 μm. The effect of the orientation, including vertical, horizontal, and up-side-down, of the nebulizer was also investigated. An aerosol size spectrometer (Welas 3000, Palas) was employed to measure the aerosol number concentration and size distribution. This nebulizer was mainly evaluated with 0.9% sodium chloride.

Results: The power consumption of this device was only 0.925 watt. It could continuously operate for over 6 hours. The feeding rate was around 0.15 mL/min and only negligibly affected by the device orientation. However, the residual was slightly influenced by the orientation, 7.0%, 5.6%, 2.6% for vertical, horizontal and upside down, respectively. The count median diameter of the aerosol output was around 0.55 μm, with geometric standard deviation about 2. The aerosol number concentrations were 6,878, 11,724, and 16,101 #/cm3 for vertical, horizontal, and upside down, respectively.

Conclusions: The most significant feature of this handheld nebulizer was almost orientation independence. This made it ideal for medical use, especially for patients lying on bed. However, there are many applications in the field of occupational hygiene, such as qualitative fit testing, and smoke stream generation. It could also become an exceptionally energy saving humidifier. The aperture size and number on the vibrating mesh plate could be change to improve the aerosol size and concentration. The residual volume could be further reduced by adjusting the design of the solution transport devise.

 

CS-12​0-04

Nearly Real-Time Particulate Counting During Remediation Projects

A. Havics, PH2, LLC, Avon, IN

Situation/Problem: Dust control is a common issue in remediation projects, both indoor and outdoor. Historically, sampling on sites has consisted of daily total, respirable dust, Total Suspended particulate (TSP), or PM10 using filters followed by gravimetric or lab-based analytical techniques. These techniques generally result in a delay of hours to days to receive data upon which to assess particulate exposure.

Resolution: Optical Particle Counters (OPCs) can be used during these projects to directly assess particle aerosolization, fate & transport on a real-time or nearly real-time basis. This use provides relatively rapid turnaround to evaluate controls, processes, as well as determining more quickly whether an airborne limit has been exceeded.

Results: Sites for illustrative purposes include a hospital mold remediation project and a few excavation/building demo locations near residential or commercial properties involving metals and general dust.

Lessons learned: A few cases where OPCs have been used, including side-by-side filter sampling, will be used to illustrate the benefits and to show the assumptions and subsequent limitations.

 

SR-12​0-05

Real-Time Particle Size Distribution Measurements of Coarse Coal Dust

T. Barone, C. Seaman, and S. Mischler, Dust, Ventilation and Toxic Substance Branch, CDC/NIOSH, Pittsburgh, PA; E. Hesse, University of Hertfordshire, Hertfordshire, United Kingdom

Objective: Aerosols with strong light scattering properties and spheroidal morphology have previously been characterized by the cloud and aerosol spectrometer (CAS). However, the CAS response for strong light absorbing and irregularly shaped coal dust has not been studied. Real-time particle size distribution (PSD) measurements would facilitate assessments of control technologies for prevention of dust explosions in underground coal mines. The primary objective of this study was to estimate coarse coal dust PSDs using CAS real-time light scattering measurements.

Methods: Ray tracing diffraction on facets (RTDF) theory was used to compute PSDs from CAS single particle forward light scattering measurements. Coal dust morphology was approximated as fractal polyhedral crystals and refractive index was based on previous measurements for a given coal rank. PSDs were estimated for test coal dust (10 - 20 µm, 20 - 32 µm, 32 - 45 µm) generated by air jet sieving and characterized using computer controlled scanning electron microscopy (CCSEM). Test dust sedimentation was prevented by: (1) aerosolization and deagglomeration using a dust disperser with a linear flow path to avoid particle impaction on tubing walls, (2) vertically aligning the disperser outlet and CAS inlet; and (3) adding high velocity HEPA filtered sheath air to prevent particle settling.

Results: PSD estimates were consistent with size ranges of coal dust generated by air-jet sieving. Sieve size separation was not ideal, in that a small particle mode remained in the large particle test dust. This is probably because electrostatic properties of the test dust prevented deagglomeration during air-jet sieving. However, the dust could be fully deagglomerated by the dust disperser, and the absence of agglomerates was confirmed by CCSEM. Although the PSDs were bimodal, the modes were distinct and overlap did not interfere with size range comparisons. The 10 - 20 µm and 20 - 32 µm modal diameters were 7 µm and 21 µm, respectively. The 32 - 45 µm test dust had a broad distribution that was confirmed by CCSEM.

Conclusions: Because estimated particle diameters agreed well with sieve based sizing, the results suggest that CAS real-time measurements can be used to determine coarse coal dust PSDs. This was enabled through the RTDF model, which includes coal dust morphology and composition effects in estimating particle diameter from CAS forward light-scattering intensities.

 

SR-1​20-06

New Methodology for Achieving Inside the Hood Sampling for Welding Operations

R. Aivazian, TCF Risk Management, Casper, WY

Objective: To determine if a comprehensive study of a new methodology of inside the hood sampling for welding operations is warranted. Current methods for sampling within the welding hood create problems of discomfort for the user. This study was a preliminary test on a new method of sampling that would create less discomfort to see if the method is feasible and would warrant further testing.

Methods: Since this study was a preliminary feasibility study, it was limited in the size and scope. Two separate sampling events were included in the study at separate facilities. In each sampling event, 6 samples were taken on 6 individual welders using traditional sampling methodologies as control samples. Additionally, each welder had a sample collected using the new methodology. The samples were submitted to an AIHA accredited laboratory, along with blanks for quality control, to be analyzed for total particulates, Antimony, Beryllium, Cadmium, Chromium, Cobalt, Copper, Iron Oxide, Lead, Manganese, Molybdenum, Nickel, Vanadium Pentoxide, and Zinc Oxide. For each sampling event, the experimental samples were compared for statistical difference from the control samples using the Mann-Whitney U-Test calculated with 2-tails and a p value of 0.05.

Results: Based on the results of the samples from the two sampling events, there is no significant differences between the concentrations found in control samples and in experimental samples in either sampling event. The first sampling event provided U values of 1.15 to 2.7 times the critical U value. The second sampling event provided U values of 1.5 to 3.3 times the critical U value. While the sample sizes were small, significant statistical differences were not observed.

Conclusions: This experimental sampling was successful. Data was obtained to determine whether or not a larger analysis of the new sampling methodology would be warranted. Based on the sampling, it is feasible that the new methodology could provide data as accurate as current sampling method provide. Based on these results, more in depth analysis of this sampling method should be conducted.

 

SR-120​-07

Effects of Pulse Parameters on Welding Fume Aerosol Size Distribution and Respiratory Deposition

J. Wang, M. Bezerra, and J. Regens, Occupational & Environmental Health, University of Oklahoma Health Sciences Center, Oklahoma City, OK

Objective: Welding fume contains various inhalation toxins such as hexavalent chromium and manganese. Occupational exposure to welding fume can cause various carcinogenic and neurological effects. The high temperature welding process creates high concentrations of nano- to submicron-sized metallic aerosols composed of toxic metals. Pulse welding targets reducing the heat input to the welding arc zone by high-frequency voltage fluctuation, as opposed to the steady voltage in nonpulse welding. Pulse welding was hypothesized to improve the weld quality, while decreasing the metal vaporization. The objective of this study is to investigate the pulse parameters (voltage, frequency, and percentage) on formation and characteristics of welding fume aerosols.

Methods: A pulse metal inert gas weld​​​er was placed in a metal fume chamber. Welding with different combinations of pulse parameters as well as baseline (non-pulse) were conducted through beading on 308L stainless steel plates. Particle size distribution was measured by a scanning mobility particle sizer and an aerodynamic particle sizer for fine and coarse particles, respectively. Respiratory deposition fractions for head airways (HA), tracheobronchial (TB), and alveolar (AL) regions were estimated based on a simplified International Commission on Radiological Protection (ICRP) model.

Results: The results indicated the dominant parameter of particle emission characteristics was pulse voltage. Pulse welding did not drastically change the geometric distribution of the particle sizes comparing to the non-pulse welding. However, pulse welding reduced the particle emissions in both fine and coarse regimes, without compromising the weld quality. Use low pulse voltage can produce the least particle number concentrations (3.0E7 #/cm3 fine particles and 0.7E4 #/cm3) and in favor of more upper respiratory tract deposition.

Conclusions: In sum, we suggest the welder should operate at a low pulse voltage to minimize the potential particle exposures.

 

SR​-120-08

Study of the Effective Vortex Length of Cyclone

H. Hung, S. Huang, C. Lin, and C. Chen, Department of Public Health, National Taiwan University, Taipei, Taiwan

Objective: In a conventional cyclone, the outer vortex flow weakens and changes its direction at a certain axial distance from the vortex finder. This axial magnitude has been called the “natural vortex length” of the cyclone. Since the space below the vortex would not be used for particle collection, cyclone designs with a natural vortex length equal to or greater than the physical length of a cyclone were recommended. However, previous studies have shown contradictory results. Therefore, the main purpose of the present study was to experimentally investigate the effect of the ‘effective vortex length’ on the performance of cyclones with different configurations.

Methods: To characterize the performance of sampling cyclones, an ultrasonic atomizing nozzle was used to generate micrometer sized potassium sodium tartrate particles. An Am-241 radioactive source was employed to neutralize the particles to the Boltzmann charge equilibrium. Aerosol size distributions and number concentrations upstream and downstream of the cyclones were measured using an Aerodynamic Particle Sizer (APS). Each aerosol penetration measurement was repeated five times to assure data quality. The pressure drop across the cyclone was measured using an inclined manometer. All types of sampling cyclones developed in this work were variations from the base design of the Very Sharp Cut Cyclone. The effective vortex length of a cyclone was analyzed by using the aerosol penetration and the pressure drop across the cyclone, and compared to the modeled data reported in previous studies.

Results: The results showed that both the 50% cut-off size and pressure drop were sensitive enough to illustrate the effect of cyclone configurations or the operation flow rate on the effective vortex length. The effective vortex length significantly increased with increasing sampling flow rate and decreasing cyclone body diameter. However, the inlet diameter, the outlet diameter, the length of vortex finder and the cyclone with or without cone had only minor influence on the effective vortex length.

Conclusions: The effective vortex length was normally in the range from 4 to 6 H/D, depending on the cyclone conformations and the power input entering the cyclone. As an indicator estimating the effective vortex length, the 50% cutoff size was more sensitive than the pressure drop. However, the pressure drop measurement was apparently easier to execute.​