Jaime Lara

Impact of two particle measurement techniques on the determination of N95 class respirator filtration performance against ultrafine particles.

The purpose of this experimental study was to compare two different particle measurement devices; an Electrical Low Pressure Impactor (ELPI) and a Scanning Mobility Particle Sizer (SMPS), to measure the number concentration and the size distribution of NaCl salt aerosols to determine the collection efficiency of filtering respirators against poly disperse aerosols. Tests were performed on NIOSH approved N95 filtering face-piece respirators (FFR), sealed on a manikin head. Ultrafine particles found in the aerosols were also collected and observed by transmission electron microscopy (TEM). According to the results, there is a systematic difference for the particle size distribution measured by the SMPS and the ELPI. It is largely attributed to the difference in the measurement techniques. However, in spite of these discrepancies, reasonably similar trends were found for the number concentration with both measuring instruments. The particle penetration, calculated based on mobility and aerodynamic diameters, never exceeded 5% for any size range measured at constant flow rate of 85 L/min. Also, the most penetrating particle size (MPPS), with the lowest filtration efficiency, would occur at a similar ultrafine size range <100 nm. With the ELPI, the MPPS was at 70 nm aerodynamic diameter, whereas it occurred at 40 nm mobility diameter with the SMPS.

Mechanical and Biomechanical Approaches for Measuring Protective Glove Adherence

Workers wearing insufficiently adherent gloves must exert additional muscular effort to grip objects, leading to discomfort, pain and even musculoskeletal disorders of the upper limbs. The main goal of this preliminary study was to explore mechanical and biomechanical approaches for characterizing glove adherence in order to verify whether a purely mechanical method can provide results that are in agreement with a biomechanical method, which takes into account the human factor. A mechanical method was developed to measure the coefficient of friction (COF) between 23 glove models and a steel surface. A biomechanical method was also developed to measure the COF at the hand/glove and glove/steel interfaces. Six subjects performed tests with three glove models, and gave their perception of glove adherence. The comparison between the biomechanical and mechanical results revealed that both methods produced similar COF values for each glove/steel interface. Those values agreed with the subjects perception. However, the biomechanical method revealed a stick-slip phenomenon for one out of the three glove models, which makes evaluation of the COF difficult. On the other hand, the proposed mechanical method is capable of measuring the static and dynamic COFs of various glove models. It also has the advantages of being simple, reproducible, and inexpensive.

Prediction of Stress-Strain Behaviour and Energy Dissipation of Textile Protective Materials at Large Deformations

The aim of this study is to develop a model for the mechanical behavior of knitted fabrics, which are used in protection gloves, at large deformation and different strain rates in terms of extension/ recovery cycling. The non-linear viscoelastic model is based on the standard solid model. The choice of this model is based on its simplicity due to the limited number of elements. It contains three nonlinear spring and damper elements. The idea is to consider that, by analogy with elastomers, the mechanical behavior of the fabric in terms of hysteresis loop is due to the contribution of two parts: the first one represents the equilibrium state of the fabric and the second one is due to the deviation from this equilibrium. Then, the stress-strain behavior of the fabric at different strain rates can be computed using the same parameters determined at one value of strain rate. The dissipated energy is provided by the area under the hysteresis loop. A good agreement has been obtained between the experimental and theoretical results.

Systematic evaluation of the adsorption of organic vapors onto a miniaturized cartridge device using breakthrough tests in parallel experiment with a full size respirator cartridge

Breakthrough experiments are essential for the characterization of the adsorption capacity and micropore volume of activated carbon respiratory cartridges and for the validation and determination of cartridge service life models. In an effort to gain better control over environmental conditions in breakthrough tests and to obtain reliable data, a novel experimental approach using a miniaturized (Mini) cartridge was designed to replicate a small section of a respiratory cartridge. The Mini device and the organic vapor respiratory cartridge were tested in single and parallel experiments where in the former, one filter was tested one at a time and in the latter both devices were exposed simultaneously to the same conditions. The Mini device gave comparable results to the 10% breakthrough times and adsorption capacities of the organic vapor cartridges. The reproducibility of the packed carbon bed of the Mini provided strong support for using the Mini in breakthrough experiments for the characterization of the activated carbon adsorption capacity and estimation of cartridge service life.