| Autor: |
Radney JG; Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States., Weaver JL; Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States.; Museum Conservation Institute, Smithsonian Institution, Suitland, Maryland 20746, United States., Vicenzi EP; Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States.; Museum Conservation Institute, Smithsonian Institution, Suitland, Maryland 20746, United States., Staymates ME; Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States., Zangmeister CD; Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States. |
| Abstrakt: |
The United States Centers for Disease Control and Prevention and World Health Organization recognize that wearing cloth face coverings can slow the transmission of respiratory diseases via source control. Adding a partial layer of material with a high filtration efficiency (FE, e . g ., polypropylene sheets that meet the HEPA standard) as an insert can potentially provide additional personal protection; however, data on the necessary areal coverage are sparse. The relationship between insert area ratio (IAR) relative to fabric area, FE, differential pressure (Δ P, a surrogate for breathability), and quality factor (QF, a ratio including FE and Δ P ) utilizing two fabrics (rayon and 100% cotton lightweight flannel) and three insert materials (HEPA vacuum bag, sterilization wrap and paper coffee filter) was investigated. The effect of inserts on particle flows mimicking human exhalation is semiquantitatively and qualitatively examined using flow visualization techniques. The following was found: (1) The relationship between FE, Δ P , and QF is complex, and a trade-off exists between personal protection from filtration during inhalation and source control from leakage during exhalation; (2) FE and Δ P of the composite covering increase with IAR, and the rate is dependent upon insert type; (3) improvements (decrements) in the QF of the composite assemblage require inserts with a higher (lower) QF than the fabric and larger differences yield greater gains (losses); (4) the increased Δ P from an insert results in increased leakage during exhalation; (5) to minimize leaks, Δ P must be as low as possible; and (6) small relative areas not covered by an insert ( i . e ., IAR slightly smaller than 1) strongly deteriorate the benefits of an insert similar to small leaks in a covering. |
