ASHRAE Journal - May 2021 - 17

TECHNICAL FEATURE

References

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FIGURE 7 Overall effective filtration efficiency for inhalation, ηf,Minh , measured for

the four masks tested in this work both with and without a mask braces (commercial brace and UW-Madison fitter).
1.0

inh

Effective Filtration Efﬁciency, ηf,M (-)

aerodynamic diameters: 0.728 µm and 2.71 µm. The
spatial distribution for the 0.728 µm aerosol size was
generally more uniform than that for the 2.71 µm size,
suggesting that a higher fraction of the larger particles
settled more rapidly compared to the smaller size
aerosols.
This result implies that smaller particle sizes may be
distributed more uniformly in the room and that the wellmixed assumption in the Wells-Riley model may hold
better for these particle sizes. Although the concentration
near the aerosol source trended higher as expected, the
measurements of the time-resolved and size-resolved
NaCl aerosol concentrations support the well-mixed
assumption for the Wells-Riley model.
Field measurements of effective ﬁltration efﬁciency
were conducted for four different mask types: a commercial four-ply knit cotton mask, a three-ply spunbond
polypropylene mask (EOC mask), a single-use three-ply
disposable procedure mask and an ASTM F2100 Level 2
rated surgical mask. The four-ply knit cotton mask had
the lowest effective ﬁltration efﬁciency at 0.075 ±0.043,
while the EOC mask had the highest effective ﬁltration
efﬁciency at 0.545 ±0.031. The Level 2 rated surgical mask
had an effective ﬁltration efﬁciency of 0.447 ±0.038.
In all cases, the effective ﬁltration efﬁciency for the
masks improved when an external mask brace or mask
ﬁtter was used to enhance mask sealing. The margin of
improvement in effective ﬁltration efﬁciency with a mask
ﬁtter was dramatic. The single-use procedure mask saw
the most signiﬁcant improvement in ﬁltration efﬁciency
with the use of a mask ﬁtter, increasing from 0.158 ±0.042
alone to 0.949 ±0.026 with the addition of a mask ﬁtter.

Commercial Brace
UW-Madison Fitter
No Fitter

0.8

0.6

0.4

0.2

0.0

Knit Cotton
Mask

EOC
Mask

Procedure
Mask

Surgical
Mask

Transmission of Coronavirus Disease 2019 (COVID-19). " Clinical
Infectious Diseases 71(9):2311 - 13. https://doi.org/10.1093/cid/ciaa939
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settings: combined impacts of ventilation and mask effective
ﬁltration efﬁciency. " Submitted to Indoor Air, preprint available at
https://www.medrxiv.org/content/10.1101/2020.12.31.20249101v1
M AY 2021

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https://www.doi.org/10.1093/cid/ciaa939 https://www.doi.org/10.1001/jama.2020.7603 https://www.doi.org/10.7554/eLife.57309 https://www.doi.org/10.7554/eLife.57309 https://www.doi.org/10.1038/s41467-020-16670-2 https://www.tinyurl.com/848emd2w https://www.tinyurl.com/9t8n6z2 https://www.tinyurl.com/f8874ubp https://www.fda.gov/emergency-preparedness-and-response/coronavirus-disease-2019-covid-19/covid-19-vaccines https://www.fda.gov/emergency-preparedness-and-response/coronavirus-disease-2019-covid-19/covid-19-vaccines https://www.tinyurl.com/dufvvszk https://covid.cdc.gov/covid-data-tracker/#vaccinations https://covid.cdc.gov/covid-data-tracker/#vaccinations https://apps.who.int/iris/handle/10665/331661 https://www.tinyurl.com/ncptdcab https://www.medrxiv.org/content/10.1101/2020.12.31.20249101v1 http://www.ashrae.org

ASHRAE Journal - May 2021

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