David Dhanraj’s research while affiliated with Washington University in St. Louis and other places

Objective: The COVID-19 pandemic has precipitated widespread shortages of filtering facepiece respirators (FFRs) and the creation and sharing of proposed substitutes (novel designs, repurposed materials) with limited testing against regulatory standards. We aimed to categorically test the efficacy and fit of potential N95 respirator substitutes using protocols that can be replicated in university laboratories. Setting: Academic medical centre with occupational health-supervised fit testing along with laboratory studies. Participants: Seven adult volunteers who passed quantitative fit testing for small-sized (n=2) and regular-sized (n=5) commercial N95 respirators. Methods: Five open-source potential N95 respirator substitutes were evaluated and compared with commercial National Institute for Occupational Safety and Health (NIOSH)-approved N95 respirators as controls. Fit testing using the 7-minute standardised Occupational Safety and Health Administration fit test was performed. In addition, protocols that can be performed in university laboratories for materials testing (filtration efficiency, air resistance and fluid resistance) were developed to evaluate alternate filtration materials. Results: Among five open-source, improvised substitutes evaluated in this study, only one (which included a commercial elastomeric mask and commercial HEPA filter) passed a standard quantitative fit test. The four alternative materials evaluated for filtration efficiency (67%-89%) failed to meet the 95% threshold at a face velocity (7.6 cm/s) equivalent to that of a NIOSH particle filtration test for the control N95 FFR. In addition, for all but one material, the small surface area of two 3D-printed substitutes resulted in air resistance that was above the maximum in the NIOSH standard. Conclusions: Testing protocols such as those described here are essential to evaluate proposed improvised respiratory protection substitutes, and our testing platform could be replicated by teams with similar cross-disciplinary research capacity. Healthcare professionals should be cautious of claims associated with improvised respirators when suggested as FFR substitutes.

The use of facemasks is proven to mitigate the spread of the coronavirus and other biological agents that cause disease. Various forms of facemasks, made using different materials, are being used extensively, and it is important to determine their performance characteristics. The size-dependent filtration efficiency and breathing resistance of household sterilization wrap fabrics, and isolation media (American Society for Testing and Materials (ASTM)- and non-ASTM-rated), were measured in filter-holder- and mannequin-in-chamber-based systems, focusing on particles sizes between 20 nm and 2 μm. Double-layer MERV-14 (Minimum Efficiency Reporting Values with rating 14) showed the highest filtration efficiency (94.9–73.3%) amongst household filter media, whereas ASTM-rated isolation masks showed the highest filtration efficiencies (95.6–88.7) amongst all the masks considered. Filtration efficiency of 3D-printed masks with replaceable filter media was found to depend on the degree of sealing around the media holder, which depended on the material’s compressibility. Filtration efficiencies of triple-layer combinations (95.8–85.3%) follow a profile similar to single layers but with improved filtration efficiencies.

Novel designs and materials for filtering face-piece respirators (FFRs) have been disseminated in response to shortages during the COVID-19 pandemic. Since filtration efficiency depends on particle diameter and air face velocity, the relevance of material filtration or prototype fit data depends on test conditions. We investigate whether characterizing a material in a filter holder at a range of face velocities enabled precise prediction of the filtration performance of a novel sewn mask design. While larger particles (> 500 nm) are more relevant for inhalation exposure to respiratory emissions, we compare this mask and a N95 FFR (as a control) with smaller particles more similar to those in the N95 test method. Sewn from sterilization wrap, our mask (sealed to a mannequin head with silicone) filters 85 ± 1% of 136 nm particles (NaCl, 85 L min–1) and passes quantitative fit tests for 4 of 6 volunteers, representing intermediate protection between a surgical mask and N95 FFR. Filter holder material measurements overpredict the sewn mask’s filtration efficiency by 8.2% (95% CI 7.4–9.1%) (136 or 200 nm). While testing flat material in a filter holder enables comparison between materials, filtration performance does not precisely scale-up from filter holder to mannequin tests. Testing full prototypes at relevant conditions is crucial if an improvised design is intended as a substitute for a commercial surgical mask or FFR.

Aerosol-driven solvent losses have been identified as one of the major challenges of amine-based post-combustion CO2 capture. In this work, a multi-component aerosol dynamics model based on the discrete-sectional approach, accounting for condensation and coagulation was coupled with a process simulation model developed using ASPEN PLUS v10® to account for the multi-component mass and heat transfer, hydrodynamics, thermodynamics, and electrolytic-solution chemistry. Particle losses inside the absorber were incorporated into the model based on a cut-off size determined from experiments reported in the literature. Based on the results, it was shown that neglecting particle losses inside the absorber resulted in a significant over-prediction of amine-based solvent losses, while coagulation of particles resulted in reduced (∼10%) amine emissions. Furthermore, amine emissions increased when the number concentration and the geometric standard deviation of inlet particles in the flue gas were increased. Moreover, it was shown that amine emissions were lower at lower solvent concentrations and temperatures. CO2 capture efficiency dropped for decreasing solvent concentration, but remained unchanged for lower temperatures, suggesting that decreasing the solvent temperature is an efficient strategy to reduce amine emissions.

The COVID-19 pandemic has caused a severe demand for facemasks, and this has resulted in the use of those made from alternate media. As SARS-CoV-2 spreads primarily due to airborne droplets, it is critical to verify the filtration efficiency of these alternate media based facemasks. While several media are being tested and used, commercially available dust cleaners have shown reasonable filtration efficiency. This may also be due to the potential electrostatic charge on the surface which enhances capture of the fine particles. In this manuscript, we report the size dependent filtration efficiency studied systematically in a filter holder-based system as 47 mm punches; and test results on a mannequin that was 3D printed wearing a bandana mask that was placed in a chamber.

An open source software (Aerosol and Air Quality Research Lab-Aerosol Dynamics Model, AAQRL-ADM) used for aerosol dynamics simulations is developed by including four models: discrete, discrete-sectional, method of moments and modal. First, the mathematical description of these models as well as the effects of aerosol dynamics available in the software are reviewed, and a modal model is developed to use multiple modes to represent particle size spectrum. Second, the design of a working principle and user graphical interface (GUI) of AAQRL-ADM is described. Third, the models in AAQRL-ADM are validated by investigating the evolution of particle size distribution (PSD) in considering the effects of coagulation, condensation and nucleation. Next, the trade-off between simulation accuracy and numerical efficiency is discussed for all of the four models, and a guide to choosing the appropriate aerosol dynamic model in practical simulation is presented. Finally, discrete-sectional, moment and modal models are used to investigate the particle size distribution in a furnace aerosol reactor along a streamline, coupled with the velocity and temperature profiles. AAQRL-ADM is provided free of charge for the use of public researchers. Copyright © 2020 American Association for Aerosol Research