Most reasoned analysis elects face masks as our most effective countermeasure against the COVID-19 pandemic. Of course, there are a lot of variables to consider as far as the application is concerned.
We know that our transmission risk either decreases or increases considerably depending on the material our mask is made out of, but what about the influence our behavior poses while wearing one?
Thankfully, a new study published in the journal Physics of Fluids employed detailed computer models to determine the expected flow patterns of small coronavirus virions released when a mask-wearing individual coughs repeatedly. The data suggest that frequent coughing can greatly reduce a mask’s efficiency.
“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,” the authors write in the new report. “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.”
Respiratory droplets and the utility of face masks
In a previously conducted study covered by Ladders, the University of Nicosia researchers concluded that droplets of saliva can travel as much as 18 feet as quickly as five seconds when an unmasked person coughs.
In light of this finding, the authors conceived of a new model in order to assess how habitual coughing fits change the aforementioned figures when the same individual is wearing a mask.
After several numerical simulation trials, each surveying how virions interact with the porous filter in a surgical mask, the authors motioned that active viral material can still travel up to one meter even when a mask is worn during periods of mild coughing.
Moreover, although a mask reduces the number of droplets that leak out the side of a mask some droplets remain.
These new calculations elevate social distancing in a time when we are least positioned to adhere to it.
In fact, the authors wrote that masks are not enough for essential health care professionals.
New risk assessments will likely urge these communities to don helmets with built-in air filters, face shields, disposable gowns, and double sets of gloves.
“Although masks will reduce droplet transmission, we should not ignore that several droplets will be transmitted away from the mask. The use of a mask will not provide complete prevention from airborne droplet transmission. The above is particularly important for both indoor and outdoor environments,” the authors conclude. “Respiratory droplets can be transmitted several meters away from the subject due to wind conditions. Therefore, social distancing remains essential when facing an evolving pandemic.”
The bulk of coronavirus transmissions occur via larger particles in secretions, (aerosol or droplets) produced by speaking, eating, coughing, and sneezing.
A four-layer cotton muslin mask can reduce the contamination of all particles by 99%. The CDC and Wake Forest University experts recommend two layers of tightly woven 100% cotton fabric, a double layer of cotton with a thread count of at least 180, or a double layer of normal cotton with a layer of flannel in between. SARS-Cov-2 remains active on cotton for about 24 hours.
CW Headley is a reporter for the Ladders and can be reached at email@example.com