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How face mask construction and materials are important to contain cough and sneeze droplets

Smallest breath droplets emerge through the face mask

The smallest droplets of breath emerge through a face mask that consists of a folded handkerchief. Despite the leakage, the spreading of the droplets is significantly impeded compared to no mask use. Photo credits: Siddhartha Verma, Manhar R. Dhanak and John Frankenfield

Simulated coughing and sneezing from mannequins are more effective with multi-layer, well-fitting cloth masks.

While the use of face masks in public has been widely recommended by public health officials over time COVID-19 A pandemic has relatively few specific guidelines for mask materials and designs. A study by Florida Atlantic University in the Physics of liquids, from AIP Publishing, is trying to better understand which types are best at fighting respiratory droplets that may contain viruses.

Siddhartha Verma and his team experimented with various material and design options to determine how well face masks block droplets when they come out of the mouth. With the help of a laser, droplets from a mannequin head could be recognized when coughing and sneezing. The group was able to map the droplet paths and investigate how different designs and materials change this path.

The authors point out the need for further quantitative analysis, but were aware of the possibility of simpler visualization.

“Although there have been some previous studies of the effectiveness of medical grade devices, we don’t have much information about the cloth-based covers that are currently the most accessible to us,” said Verma. “We hope that the visualizations presented in the paper help to explain the reasons for the recommendations on social distance and the use of face masks.”

The approach is based on a laser blade construction, which is a mainstay for those dealing with fluid mechanics. Verma compares this to seeing dust particles in a sunbeam.

“The biggest challenge is to portray a cough and sneeze faithfully,” he said. “The setup we used was a simplified cough that is actually complex and dynamic.”

The group found that loosely folded face masks and headscarf-style covers reduced the distance covered by the droplet jets by between 1/8 and 1/2 the distance for an uncovered cough. However, well-made homemade masks with several layers of quilting fabric and commercially available cone masks proved to be the most effective. Despite some leaks, these masks significantly reduced the number of droplets.

Without a mask, the mannequins projected droplets much further than the often-quoted 6 feet in social distance guidelines.

Verma said the group would like to continue investigating the complex interplay, which may include droplet evaporation, ambient airflow, and the properties of the exhaled respiratory fluid that cause droplets to behave.

“It is also important to understand that face coverings are not 100% effective in blocking respiratory pathogens,” he said. “For this reason, it is imperative that we use a combination of social distancing, face covering, hand washing, and other recommendations from health officials until an effective vaccine is released.”

For more information on this research, see Comparing the Effectiveness of Face Masks in Attenuating Transmission of COVID-19.

Reference: “Visualization of the effectiveness of face masks in the obstruction of respiratory rays” by Siddhartha Verma, Manhar Dhanak and John Frankenfield, June 30, 2020, Physics of liquids.
DOI: 10.1063 / 5.0016018

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