Effectiveness of cloth masks depends on type of covering

Date:
August 25, 2020
Source:
American Institute of Physics
Summary:
Wearing a mask while out in public has become the recommended
practice during the COVID-19 pandemic. Researchers have now
experimentally visualized the flow fields of coughs under various
common mouth covering scenarios.



FULL STORY ========================================================================== Months into the COVID-19 pandemic, wearing a mask while out in public
has become the recommended practice. However, many still question the effectiveness of this.


==========================================================================
To allay these doubts, Padmanabha Prasanna Simha, from the Indian
Space Research Organisation, and Prasanna Simha Mohan Rao, from the Sri Jayadeva Institute of Cardiovascular Sciences and Research, experimentally visualized the flow fields of coughs under various common mouth covering scenarios. They present their findings in the journal Physics of Fluids,
from AIP Publishing.

"If a person can reduce the extent of how much they contaminate the
environment by mitigating the spread, it's a far better situation for
other healthy individuals who may enter places that have such contaminated areas," Simha said.

Density and temperature are intricately related, and coughs tend to be
warmer than their surrounding area. Tapping into this connection, Simha
and Rao utilized a technique called schlieren imaging, which visualizes
changes in density, to capture pictures of voluntary coughs from five
test subjects. By tracking the motion of a cough over successive images,
the team estimated velocity and spread of the expelled droplets.

Unsurprisingly, they found N95 masks to be the most effective at reducing
the horizontal spread of a cough. The N95 masks reduced a cough's initial velocity by up to a factor of 10 and limit its spread to between 0.1
and 0.25 meters.

An uncovered cough, in contrast, can travel up to 3 meters, but even a
simple disposable mask can bring this all the way down to 0.5 meters.

"Even if a mask does not filter out all the particles, if we can prevent
clouds of such particles from traveling very far, it's better than
not doing anything," said Simha. "In situations where sophisticated
masks are not available, any mask is better than no mask at all for the
general public in slowing the spread of infection." Some of the other comparisons, however, were striking.

For example, using an elbow to cover up a cough is typically considered
a good alternative in a pinch, which is contradictory to what the pair
found. Unless covered by a sleeve, a bare arm cannot form the proper
seal against the nose necessary to obstruct airflow. A cough is then
able to leak through any openings and propagate in many directions.

Simha and Rao hope their findings will put to rest the argument that
regular cloth masks are ineffective, but they emphasize that masks must continue to be used in conjunction with social distancing.

"Adequate distancing is something that must not be ignored, since masks
are not foolproof," Simha said.


========================================================================== Story Source: Materials provided by American_Institute_of_Physics. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Padmanabha Prasanna Simha, Prasanna Simha Mohan Rao. Universal
trends in
human cough airflows at large distances. Physics of Fluids, 2020;
32 (8): 081905 DOI: 10.1063/5.0021666 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200825113635.htm

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