Performance of Composite Filters Assembled from Multiple Layers of Basic Filtration Media

Abstract

There is a severe shortage of face masks and N95 respirators due to the current COVID-19 pandemic, particularly in countries that were not well prepared in advance. In order to help ease the supply demands of these resources, a strategy of using multiple layers of basic filtration media to construct a composite filter that can match the particle collection efficiency offered by a N95 filtering facepiece respirator (FFR) is proposed. In this study, the filtration performances of four face masks and one N95 respirator using the same test protocol (as a reference) were first compared. Composite filter samples composed of multiple layers of basic face mask and MERV13 furnace media were then constructed and the filter performance of the composite filters was investigated. As expected, the minimum particle collection efficiency of the N95 respirator media sample was higher than 95% and the efficiency of the samples from the four tested face masks varied from 71.8% to 83.6%. The Figure of Merit (FOM) values of the face mask samples were generally half that of the N95 media sample. It was found that a N95-comparable collection efficiency can be achieved by combining two/three layers of face mask media but at the expense of a higher media pressure drop. Additionally, the composite filter samples made up of three/five layers of MERV13 furnace media could approach the FOM offered by the N95 media without the increased pressure drop. It was also found that the measured collection efficiency of multiple-layered filter media was not equal to the calculated in the test particle size range. Further studies are required to identify the reason(s).

On the Filtration Efficiency of Composite Media Composed of Multiple Layers of Electret Media

“…3 shows the comparison between the measured and calculated collection efficiencies of the double-layered electret media when challenged by particles with the Boltzmann stationary charge distribution. Differences between the measured and calculated data were only observed in a certain size range of particles (as reported by Wang et al, 2020) for both double-layered electret media.…”

“…Composite media composed of multiple layers of electret media (in different specifications) have been found to offer better filtration performance than that of homogenous electret media (Leung et al, 2009;Leung et al, 2018;Tang et al, 2018a;Chang et al, 2019;Sun and Leung, 2019;Tien et al, 2020). In our previous study (Wang et al, 2020), the initial collection efficiency of composite media made of multiple electret medium layers of the same specification were measured using size-fractionated particles in the Boltzmann stationary charge distribution. It was found that the measured filtration efficiency of the multi-layered composite electret media was lower than the calculated value, assuming each electret medium layer functions independently.…”

Mask Material Filtration Efficiency and Mask Fitting at the Crossroads: Implications during Pandemic Times

“…Whereas some studies use a manikin headform with the full mask (Balazy et al, 2006a,b;He et al, 2013;Bahloul et al, 2014;Shakya et al, 2016;Adhikari et al, 2018;Kumar et al, 2020), other studies cut a portion of the mask/fabric and place it in a filter holder (Eshbaugh et al, 2008;Lin et al, 2017;Konda et al, 2020;Pei et al, 2020;Wang et al, 2020). Many studies use salt, e.g., NaCl (Eshbaugh et al, 2008;He et al, 2014;Lin et al, 2017;Pei et al, 2020), or polystyrene latex (PSL) spherical particles of defined sizes (Qian et al, 1997;Lee et al, 2005;Eshbaugh et al, 2008) to simulate particulate contaminants.…”

“…The aerosol transmission via speaking involves generation of a large number of small (<2 µm) droplets per second (Morawska et al, 2009;Asadi et al, 2019). These aerosols play an important role in spreading the infection (Morawska and Cao, 2020;Stadnytskyi et al, 2020;Wang and Du, 2020).…”

Particle Collection of Electret Media under Different Filtration Pressures

“…They are polymer materials (produced from polymer solutions) and polypropylene (produced from its melt). In addition, the studies on composite charged media to achieve high-efficiency filtration have also been reported by Wang et al (2020) and Tang et al (2018). Charging filtration media are manufactured by several processes, including the corona charging, triboelectric charging, induction charging, and hydro charging.…”