Browsing by Subject "Penetration"
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Item Evaluation and development of methods for measurement of penetration of filtering facepiece respirators(2015-07) Satish, SwathiElevated concentrations of diesel exhaust have been linked to adverse health effects. Filtering facepiece respirators (FFRs) are widely used as a form of respiratory protection against diesel particulate matter (DPM) in occupational settings. The objective of this study was to evaluate NIOSH-certified R95 and P95 electret respirators challenged with Diesel exhaust and get a better understanding of the factors that influence penetration. Two techniques were employed for the measurement of penetration: (a) particle counting technique using a Scanning Mobility Particle Sizer (SMPS, TSI Inc.) which measures particle size distribution, and (b) Gravimetric analysis using polyfluortetraethylene (PTFE) and polypropylene (PP) filters. Gravimetric measurements using PP filters were variable compared to SMPS measurements and biased high as a result of the adsorption of gas-phase semi-volatile material. Relatively inert PTFE filters adsorbed less semi-volatile material resulting in more accurate measurements. To attempt to correct for these artifacts associated with adsorption of semi-volatile material, primary and secondary filters were used in series upstream and downstream of the FFR. Correcting for adsorption by subtracting the secondary mass from the primary mass improved the result for both PTFE and PP filters but this correction is subject to “equilibrium” conditions that depend on sampling time and the concentration of particles and semi-volatile material. Overall, the results demonstrate that great care must be taken when using filters to determine filtration efficiency of FFRs challenged with diesel exhaust. Pure PTFE or other filters that minimize adsorption of semi-volatile artifacts and two filters should be used in tandem to allow correction for adsorbed artifacts. Analysis of SMPS measurements indicated that the respirators behave differently for Diesel exhaust generated at light and heavy load on engine. At light load, the penetration of the R-95 and P-95 respirators showed a steep increase with time, exceeding the maximum allowed penetration of 5% after about 40 minutes. Whereas at heavy load, the respirators were found to have a relatively unchanging penetration (less than 5%) throughout the 90-minute test duration. This difference was attributed to the presence of a high concentration of organic carbon (OC) in Diesel exhaust which has a tendency to degrade the electric charges on the respirators, thus reducing the filtration enhancement from electrostatic attraction forces. To account for the complex nature of DPM and its varying properties with changes in operating and sampling condition, an oxidation-dilution tunnel was designed to produce Diesel exhaust with a controlled set of properties: elemental carbon (EC) concentration, OC concentration, EC/OC ratio and volume flow rate. This device was used to evaluate R-95 and P-95 respirators for solid Diesel exhaust aerosol. The methodology proved to be effective in controlling the EC concentration and total volume flow rate. Results showed that the R-95 and P-95 respirators were more than 95% efficient for solid Diesel exhaust aerosol. This thesis is divided into two parts. The first focuses on the measurement of penetration of FFRs for Diesel exhaust, the second on the development of a standard DPM generator for testing filtration systems.Item Penetration of Ar and He RF-driven plasma jets into micrometer sized capillary tubes(2018-07) Brahme, AmitaThe penetration and propagation of cold atmospheric pressure plasmas into volumes having sub-millimeter to micrometer sizes with large aspect ratios is required for enabling an effective disinfection of the inside of catheter tubes, tooth cavities, skin pores and enhance plasma catalysis in porous catalysts. As filamentary plasmas have often a characteristic diameter on the same length scale as tubes or pores, the penetration of plasma in these tubes and pores is not a priori obvious and can have a huge effect on the plasma properties. Particularly for medical applications, especially on teeth and skin, it is important that the plasma operates at low voltages and near ambient gas temperatures. This study has a goal to complement existing research in this area that has mainly been focused on pulsed discharges with significant overvoltage. We report on a study using RF driven argon and helium plasma jets with the plasma generation outside the capillary followed by its penetration and propagation inside the capillary. We present the experimental determination of the limitations on the penetration diameter, and the underpinning mechanisms of the plasma propagation and penetration process. Experimental results include time resolved imaging of plasma propagation and penetration in capillaries with different internal diameter and report surface electric field measurements. We found that the time between the plasma jet in first contact with the capillary tube surface and the subsequent penetration into the capillary tube spans several RF cycles due to electric fields at the plasma-tube interface below 4 kV/cm. These low electric fields require Penning ionization and/or stepwise ionization and hence a build up of the metastable and electron density to achieve a locally sufficiently large ionization rate to enable penetration and propagation. Furthermore, it is found that the propagation of the argon jet into the capillary occurs during the positive half cycle of the RF waveform and is very similar to the propagation of the jet in surrounding air.