Evaluation of Mask and Mask Material Suitability for COVID-19 Transmission Protection and Influence of Face Velocity and Exhaled Breath Condensate on Filtration Efficiency
Creators: Quecke, Emily
Publisher: name: University of Alberta Library
Year: 2022

<p>Facemask use has been a key public health measure in response to the SARS CoV-2 pandemic; they are used to reduce airborne transmission of the disease amongst the public. The facemasks used by the public are non-medical in nature and therefore are not regulated like medical masks. Cloth masks, both commercially sourced and homemade have been used throughout the pandemic. Cloth mask suitability for protection from transmission of SARS-CoV-2 is still being determined, while new research is emerging, knowledge is limited on this topic, especially due to the variety in materials and use scenarios. Understanding filtration efficiencies of different materials in different use scenarios is key for public health during this and potentially future respiratory infectious disease outbreaks. <br>
A testing line using NaCl challenge aerosol is used to evaluate the filtration efficiency and pressure drop for a variety of materials, commercially sourced non-medical masks, and medical masks. The testing line and procedure is closely adapted from the ASTM F2299 testing method used for testing medical masks. Materials and masks were tested individually as well as in various combinations. Four mask types were also tested at four different face velocities, three within the acceptable face velocity range allowed for ASTM F2299 certification and the other masks and materials were tested at two face velocities. Masks were also exposed to aerated simulated exhaled breath condensate (EBC) for 1 to 24 hours and their filtration efficiency was tested immediately following exposure. Both hygroscopic and hydrophobic masks were tested after exhaled breath condensate exposure. Statistical analysis was used to identify correlation between breath condensate exposure duration and filtration efficiency and pressure drop.<br>
Filtration efficiencies at 0.15 µm at a face velocity of 25 cm/s for commercial cloth masks, disposable non-medical masks, medical masks, commercial mask combinations and homemade combinations were, 16-29%, 39-76%, 91-97%, 51-95%, 45-94% respectively. The quality factors (QF) for this data ranged from 2.3 to 36 kpa-1. On average, the filtration efficiency decreased as face velocity of the challenge aerosol stream increased. The only masks that did not follow this trend were the woven and knitted materials and two of the commercial masks made with cotton. Filtration efficiency decreased by up to 20% after EBC exposure. Two masks had statistically significant correlations between filtration and EBC exposure time at 1.0 µm; other masks showed similar trends but were not statistically significant. There was no strong correlation between EBC exposure and pressure drop.<br>
With proper layering, household materials can achieve high filtration efficiency and breathability requirements similar to medical masks. More regulation of disposable and cloth masks are needed considering the large variety in masks quality. The velocity range allowed for medical mask testing as per ASTM F2299 is too large and should be revised. Filtration efficiency varies within this range which means masks that are all certified under this standard can be inconsistent. Cloth masks should be removed and cleaned after an 8-hour workday. If possible, removal after 4-hours would be preferred. Medical and non-medical disposable masks are not largely impacted by breath condensate and therefore should be worn according to manufacturer&#39;s specifications. Further research should be conducted on the subject of how filtration mechanisms are impacted by breath condensate and on the subject of mask maintenance and lifespan which was not included in this scope.</p>