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BMJ Open ; 11(9): e045557, 2021 09 02.
Article in English | MEDLINE | ID: mdl-34475144


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.

COVID-19 , Occupational Exposure , Respiratory Protective Devices , Adult , Equipment Design , Humans , N95 Respirators , Pandemics/prevention & control , SARS-CoV-2 , United States , Ventilators, Mechanical
Materials (Basel) ; 14(8)2021 Apr 09.
Article in English | MEDLINE | ID: mdl-33918714


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.

J Environ Manage ; 290: 112690, 2021 Jul 15.
Article in English | MEDLINE | ID: mdl-33901829


Pressurized oxy-combustion is an emerging and more efficient technology for carbon capture, utilization, and storage than the first generation (atmospheric) oxy-combustion. NOx is a major conventional pollutant produced in pressurized oxy-combustion. In pressurized oxy-combustion, the utilization of latent heat from moisture and removal of acid gases (NOx and SOx) are mainly conducted in an integrated direct-contact wash column. Recent studies have shown that NOx particular inlet concentration should be maintained before direct contact wash column to remove NOx and SOx efficiently. As a result, minimizing NOx for environmental reasons, avoiding corrosion in carbon capture, utilization, and storage, and achieving effective NOx and SOx removal in direct contact wash columns are crucial. Reburning is a capable and affordable technology for NOx reduction; however, this process is still less studied at elevated pressure, particularly in pressurized oxy-combustion. In this paper, the kinetic evaluation and optimization study on NOx reduction by reburning under pressurized oxy-combustion was conducted. First, the most suitable mechanism was selected by comparing the results of different kinetic models with the experimental data in literature at atmospheric and elevated pressures. Based on the validated mechanism, a variety of parameters were studied at high pressure, i.e., comparing the effects of oxy and the air environment, different reburning fuels, residence time, H2O concentration, CH4/NO ratio, and equivalence ratio on the NO reduction. The results show that de-NOx efficiency in an oxy environment is significantly enhanced compared to the air environment. Improvement in the de-NOx efficiency is considerably higher with a pressure increase of up to 10 atm, but the effect is less prominent above 10 atm. The formation of HCN is significantly reduced while the N2 formation is enhanced as the pressure increases from 1 to 10 atm. The residence time required for the maximum NO reduction decreases as the pressure increases from 1 atm to 15 atm. At the higher pressure, the NO reduction rises prominently when the ratio of CH4/NO increases from 1 to 2; however, the effect fades after that. At higher pressure, the NO reduction by CH4 reburning decreases as the H2O concentration increases from 0 to 35%. The optimum equivalence ratio and high pressure for maximum NO reduction are 1.5 and 10 atm, respectively. This study could provide guidance for designing and optimizing a pressurized reburning process for NOx reduction in POC systems.

Air Pollutants , Gases , Air Pollutants/analysis , Hot Temperature , Kinetics
ACS Omega ; 3(1): 906-916, 2018 Jan 31.
Article in English | MEDLINE | ID: mdl-31457937


It has been demonstrated that atomic layer deposition (ALD) provides an initially safeguarding, uniform ultrathin film of controllable thickness for lithium-ion battery electrodes. In this work, CeO2 thin films were deposited to modify the surface of lithium-rich Li1.2Mn0.54Ni0.13Co0.13O2 (LRNMC) particles via ALD. The film thicknesses were measured by transmission electron microscopy. For electrochemical performance, ∼2.5 nm CeO2 film, deposited by 50 ALD cycles (50Ce), was found to have the optimal thickness. At a 1 C rate and 55 °C in a voltage range of 2.0-4.8 V, an initial capacity of 199 mAh/g was achieved, which was 8% higher than that of the uncoated (UC) LRNMC particles. Also, 60.2% of the initial capacity was retained after 400 cycles of charge-discharge, compared to 22% capacity retention of UC after only 180 cycles of charge-discharge. A robust kinetic of electrochemical reaction was found on the CeO2-coated samples at 55 °C through electrochemical impedance spectroscopy. The conductivity of 50Ce was observed to be around 3 times higher than that of UC at 60-140 °C. The function of the CeO2 thin-film coating was interpreted as being to increase substrate conductivity and to block the dissolution of metal ions during the charge-discharge process.

Rev Sci Instrum ; 89(2): 025109, 2018 Feb.
Article in English | MEDLINE | ID: mdl-29495807


In pulverized coal burners, coal particles usually transition from a locally reducing environment to an oxidizing environment. The locally reducing environment in the near-burner region is due to a dense region of coal particles undergoing devolatilization. Following this region, the particles move into an oxidizing environment. This "reducing-to-oxidizing" transition can influence combustion processes such as ignition, particulate formation, and char burnout. To understand these processes at a fundamental level, a system is required that mimics such a transition. Hence, we have developed and characterized a two-stage Hencken burner to evaluate the effect of the reducing-to-oxidizing transition and particle-to-particle interaction (which characterizes dense region of coal particles) on ignition and ultrafine aerosol formation. The two-stage Hencken burner allows coal particles to experience a reducing environment followed by a transition to an oxidizing environment. This work presents the results of the design and characterization of the new two-stage Hencken burner and its new coal feeder. In a unique approach to the operation of the flat-flame of the Hencken burner, the flame configurations are operated as either a normal flame or inverse flame. Gas temperatures and oxygen concentrations for the Hencken burner are measured in reducing-to-oxidizing and oxidizing environments. The results show that stable flames with well-controlled conditions, relatively uniform temperatures, and species concentrations can be achieved in both flame configurations. This new Hencken burner provides an effective system for evaluating the effect of the reducing-to-oxidizing transition and particle-to-particle interaction on early-stage processes of coal combustion such as ignition and ultrafine particle formation.