Analytical and Numerical Investigation of the Airflow in Face Masks used for Protection against COVID-19 Virus –Implications for Mask Design and Usage

Abstract

The use of face masks for the general public has been suggested in literature as a means to decrease virus transmission during the global COVID-19 pandemic. However, literature findings indicate that most mask designs do not provide reliable protection. This paper investigates the hypothesis that the impaired protection is mainly due to imperfect fitting of the masks, so that airflow, which contains virus-transporting droplets, can leak through gaps into or out of the mask. The fluid dynamics of face masks are investigated via analytical and numerical computations. The results demonstrate that the flow can be satisfactorily predicted by simplified analytical 1D-flow models, by efficient 2D-flow simulations and by 3D-flow simulations. The present results show that already gap heights larger than 0.1mm can result in the mask not fulfilling FFP2 or FFP3 standards, and for gap heights of ca. 1mm most of the airflow and droplets may pass through the gap. The implications of these findings are discussed and improvements to existing mask designs are suggested.

Proposal of a Mask and Its Performance Analysis with CFD for an Enhanced Aerodynamic Geometry That Facilitates Filtering and Breathing against COVID-19

“…This causes the greatest amount of flow to enter and exit through the gaps between the face and the seal of the mask. Ninety-five percent of the air enters and exits through different areas, such as the upper part of the nose, because it does not have an airtight seal with the face, a situation that occurs with the majority of users of this type of mask [26][27][28]30,32].…”

“…For the FFR-KN95 mask, the operating scenario was constructed considering the case with a hermetic perimeter seal with a gap of 1.3 cm 2 in the upper area of the nose. For all simulation cases, the values of the mouth opening area of 4.25 cm 2 were conserved and for each nostril of 0.78 cm 2 , as described in literature [23,26,32]. The area of the KN95 respirator was established at 114 cm 2 according to the actual dimensions of the product.…”

“…This situation causes a greater dispersion of unfiltered air that favors the danger of infection between individuals. Peric and Peric [32] conducted an investigation using numerical simulation to evaluate the design and flow inside a mask used as protection against COVID-19. They analyzed the exhalation and inhalation flow with air flow rates of up to 3095 L/min considering gaps with different geometric shapes and in different areas of the face (on the nose, close to the eyes).…”

Particle leakage through the exhalation valve on a face mask under flow conditions mimicking human breathing: A critical assessment

“…During the inhalation stage, the air flow may be also leaked through the incomplete face seal ( Bellin and Hinds, 1990 ). According to Perić and Perić (2020) , however, the flow locally accelerated along the gap between the face and perimeter of the mask during the inhalation did not change the global flow in the inspiratory direction to the extent such that it affects the operation of the exhalation valve, but only brought a slight decrease in the pressure drop across the mask. Therefore, the results obtained in the present condition are not affected by such flow structures.…”

A critical review on the role of leakages in the facemask protection against SARS‐CoV‐2 infection with consideration of vaccination and virus variants

“…The leaking fraction as a function of the total flow penetrating a mask at inhalation and exhalation has been derived from the pressure drop generated by both the mask (determined by the resistance of the fabric) and the gaps (determined by its dimensions) in an analytical model. 93 The framework has been validated with complementary CFD modeling providing additional data such as the pressure and velocity distribution within the volume enclosed by the mask and the wearer's face. A similar work proposed an analytical method combined with CFD modeling to derive the filtration ratio and the fit factor as a function of the pressure drop and the cross‐section of the gap.…”