Face masks slowly spread COVID-19;; Types of masks, duration of use are important.
The use of face masks to slow the spread of COVID-19 has been widely recommended by health professionals. This has sparked studies into the physics of face mask use and the transmission of disease, as well as research into materials, design, and other issues that affect the way face masks work.
in the Physics of liquidsFrom AIP Publishing, researchers looked at research on face masks and how to use them, summarizing what we know so far about the way face masks filter or block the virus. They also summarize design issues that have yet to be addressed.
A key aspect of the face mask function is the size of droplets of liquid expelled from the nose and mouth when a person speaks, sings, sneezes, coughs, or simply breathes. Larger droplets, around 5-10 microns in size, are most common. However, these droplets are still quite small. For comparison: a human hair is around 70 micrometers in diameter.
Volume of the proportion of breathing air at the beginning / peak of inspiration and expiration under the ventilation rates of 7.5 liters per minute (cases I) and 15 liters per minute (cases II). The color in blue represents the volume that is taken up by pure fresh air, while the red color represents the volume that is taken up by pure breathing air. The colors in between represent a mixture of fresh and breathable air. Photo credit: Heow Pueh Lee
Even smaller droplets that are less than 5 microns are potentially more dangerous. These can be aerosolized and float in the air for a long time. Of the many types of masks used (cloth masks, surgical masks and N95 masks), only N95 droplets the size of an aerosol can filter out.
The performance of face masks worn for many hours, e.g. Healthcare or other key employees affect how effective mask wear can be overall. Thermal comfort is an important issue, especially in hot and humid environments.
The researchers found that face masks made from hybrid polymer materials can filter particles with high efficiency while cooling the face at the same time. The fibers used in these special masks are transparent to infrared radiation so that heat can escape from under the mask.
“There could be a relationship between the breathing resistance and the flow resistance of the face mask that needs to be investigated for an interval between wearing the face mask,” said author Heow Pueh Lee. “In addition, the environmental conditions in the compartment inside the face mask must be quantified more precisely using miniaturized sensors and the development of human replicas for such studies.”
The researchers also reviewed epidemiological studies to find out if face masks reduced effective reproductive numbers. When the reproduction number falls below 1, the epidemic stops spreading. One study used COVID-19 data from New York state.
“The results suggest that consistent use of efficient face masks such as surgical masks could lead to the pandemic eradication if at least 70% of residents consistently use such masks in public,” said author Sanjay Kumar. “Even less efficient cloth masks could slow down the spread if they are worn regularly.”
Reference: “The perspective of the liquid flow behavior of respiratory droplets and aerosols through the face masks in the context of SARS-CoV-2By Sanjay Kumar and Heow Pueh Lee on November 24, 2020 Physics of liquids.
DOI: 10.1063 / 5.0029767
