Special Issue on COVID-19 Aerosol Drivers, Impacts and Mitigation (X)

ORIGINAL RESEARCH
https://doi.org/10.4209/aaqr.2020.07.0403

participants (men and women). They found that surgical face masks were rated significantly
lower for perceptions of humidity, heat, breath resistance and overall discomfort than N95 face
masks. Carbon dioxide was not among the investigated parameters. The aim of the study
conducted by Lim et al. (2006) was to determine the prevalence of headaches from the use of
N95 face masks amongst healthcare workers. Approximately 40% of the participants reported
face-mask-associated headaches. The study conducted by Roberge et al. (2010) assessed the
physiological impact of N95 filtering face-piece respirators on healthcare workers. The
parameters assessed included the concentration of carbon dioxide and oxygen in the mask’s dead
space. The detected carbon dioxide concentrations were around 3% (30000 ppm). Such high
concentrations are typically associated with detrimental physiological effects such as headache,
anxiety and confusion. In the study, the sampling was done via a sampling line attached to a port
in the mask that was equidistant between the nose and the mouth and therefore probably
measured the slightly diluted carbon dioxide concentration in the exhaled air rather than in the
breathing zone. Another study explored the effects of face masks (cloth mask and paper face
masks) on CO2, heart rate, respiration rate and oxygen saturation on instructor pilots (Dattel et
al., 2020). Also in this study relatively high carbon dioxide concentrations (around 45000 ppm)
were detected. The methodological description however does not allow the unequivocal
identification of the exact sampling point, making it impossible to assess whether the measured
concentrations refer to the exhaled air or to the breathing zone.
This study aimed to determine the concentration of carbon dioxide in the breathing zone while
wearing a face mask. Three types of face masks were tested under different conditions (office
work, slow walking and fast walking). The measured concentrations were compared against
existing threshold values for critical levels of carbon dioxide.

2 MATERIALS AND METHODS
2.1 Tested Face Masks
Three different types of face masks were tested:
a) A medical face mask (also known as a surgical mask) conform with the European Union’s
health and safety standards (CE mark): This type of face mask is typically used by health care
workers, ensuring a barrier that limits the transition of an infective agent between the
hospital staff and the patient. During the COVID-19 pandemic, surgical face masks have been
recommended as a means of source control for persons who are either symptomatic or
asymptomatic to prevent the spread of respiratory droplets produced by coughing or
sneezing. The application of medical masks as source control has been shown to decrease the
release of respiratory droplets carrying respiratory viruses (Leung et al., 2020) and they are
recommended for the reduction of transmission of influenza (Cheng et al., 2010; MacIntyre
and Chughtai, 2015; MacIntyre et al., 2015). Medical masks comply with requirements defined
in European Standard EN 14683:2019 (European Committee for Standardization, 2019).
b) KN95 with a one-way valve: N95 is an American standard managed by NIOSH, which is part
of the Centers for Disease Control (CDC). KN95 masks are the equivalent Chinese standard
for masks. Both N95 and KN95 correspond to the FFP2 code used in the European Union
(European Committee for Standardization, 2001) and protect against solid and liquid irritating
aerosols with a minimum filter efficiency of 92%. The mask tested in this work included a oneway exhalation valve that makes it easier to breathe through. This type of mask is not
recommended as an effective barrier against the SARS-CoV-2 virus because the valve releases
unfiltered air when the wearer breathes out and therefore does not prevent the wearer from
spreading the virus. It was included in the study to assess the potential impact of the
exhalation valve on the concentration of accumulated carbon dioxide.
c) Cloth masks: Since surgical and FFP2 masks were sometimes difficult to find at the beginning
of the pandemic and, especially the FFP2 masks should be reserved for health care providers,
cloth masks have become popular during the pandemic as they are cheap, easy to find or to
make and can be washed and reused. Cloth masks can be made from common materials, such
as sheets made of tightly woven cotton, and should include multiple layers of fabric. There are
no standards or regulations for self-made cloth face masks. The mask used in this study was
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Volume 21 | Issue 2 | 200403