On respiratory droplets and face masks

Abstract

Face mask filters—textile, surgical, or respiratory—are widely used in an effort to limit the spread of airborne viral infections. Our understanding of the droplet dynamics around a face mask filter, including the droplet containment and leakage from and passing through the cover, is incomplete. We present a fluid dynamics study of the transmission of respiratory droplets through and around a face mask filter. By employing multiphase computational fluid dynamics in a fully coupled Eulerian–Lagrangian framework, we investigate the droplet dynamics induced by a mild coughing incident and examine the fluid dynamics phenomena affecting the mask efficiency. The model takes into account turbulent dispersion forces, droplet phase-change, evaporation, and breakup in addition to the droplet–droplet and droplet–air interactions. The model mimics real events by using data, which closely resemble cough experiments. The study shows that the criteria employed for assessing the face mask performance must be modified to take into account the penetration dynamics of airborne droplet transmission, the fluid dynamics leakage around the filter, and reduction of efficiency during cough cycles. A new criterion for calculating more accurately the mask efficiency by taking into account the penetration dynamics is proposed. We show that the use of masks will reduce the airborne droplet transmission and will also protect the wearer from the droplets expelled from other subjects. However, many droplets still spread around and away from the cover, cumulatively, during cough cycles. Therefore, the use of a mask does not provide complete protection, and social distancing remains important during a pandemic. The implications of the reduced mask efficiency and respiratory droplet transmission away from the mask are even more critical for healthcare workers. The results of this study provide evidence of droplet transmission prevention by face masks, which can guide their use and further improvement.

Bacterial Dispersion Associated With Various Patient Face Mask Designs During Simulated Intravitreal Injections

“…The COVID-19 pandemic has necessitated universal face mask protocols for infection control, which has resulted in significant interest in understanding face mask effectiveness from various disciplines, 11 , 15 , 16 , 17 including ophthalmology 18 . However, there are few data on how patient face mask use may alter bacterial dispersion during an intravitreal injection, which subsequently may affect the risk of post-injection endophthalmitis.…”

“…It is possible that the tight-fitting face without tape may result in a greater amount of bacterial dispersion upward toward the subject’s eye. 12 , 17 Indeed, a recent study assessing respiratory droplet velocities with face mask use during simulated coughs reported that even with tight-fitting face masks, small openings can lead to leakage of droplets around the mask. 17 However, our study suggests that securing the superior portion of the same, tight-fitting face mask with adhesive tape significantly decreased the amount of bacterial growth, suggesting that securing the superior portion of the mask with tape may create an important barrier for upward bacterial dispersion.…”

Reciprocal Personal/Public Protection for COVID-19 with Facepiece Discriminating Mouth and Nose

“…Wilkes etc. [22] observed the same effect in the breathing system's HEPA filters used during anaesthesia, They hypothesise that the viruses, released from the droplet after contact with moisture accumulated on the filter, can be driven onwards by the flow of gas.…”

Jet Fans in the Underground Car Parks and Virus Transmission 

“…They found that respiratory droplets could travel unexpected considerable distances depending on the high-speed wind conditions. Dbouk and Drikakis [19] also demonstrated that respiratory droplets from coughing or sneezing traveled a distance less than 2 m in the case of zero-wind conditions. Bourouiba [20] found that expelled respiratory droplets during human sneezing could travel up to 7-8 m at 36 km/h -108 km/h wind speeds.…”