Abstract View
Practical Considerations of Cloth Facemask Performance Versus Insert Areal Coverage
JAMES RADNEY, Christopher Zangmeister, National Institute of Standards and Technology
Abstract Number: 123
Working Group: Infectious Aerosols in the Age of COVID-19
Abstract
The CDC and WHO recognized that wearing cloth face coverings can slow transmission of respiratory diseases; specifically, the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). Adding a layer of material with a high filtration efficiency (FE, e.g. polypropylene sheets that meet the HEPA standard) as an inset in the mask can potentially provide the wearer with additional personal protection; however, data on the insert areal coverage necessary to realize benefits is sparse. The relationship between insert area ratio (IAR, relative to fabric area), FE, differential pressure (ΔP, a surrogate for breathability) and quality factor (QF, a ratio of FE to ΔP) utilizing two fabrics (rayon and 100 % cotton lightweight flannel) and three insert materials (HEPA vacuum bag, sterilization wrap and paper coffee filter) was investigated. It was found that: 1) The relationship is complicated, and a tradeoff exists between personal protection from filtration during inhalation and source control from leakage during exhalation. 2) The addition of any insert to a cloth mask assemblage will increase both FE and ΔP, but not necessarily QF. 3) FE, ΔP and QF of the composite mask scale with IAR. 4) Improvements in the QF of the composite assemblage require inserts with a higher QF than the cloth and larger differences yield greater gains. However, the converse is also true with lower QF inserts decreasing the QF of the system. 5) The increased ΔP from an insert results in increased leakage during exhalation and 6) to minimize leaks, ΔP must be as low as possible.