COVID-19: Most homemade masks block large cough droplets, even as single layer, says study
Washington: Scientists examined the effectiveness of common household fabrics used in homemade masks in blocking droplets generated by coughing and sneezing, and have found that they are considerably protective even as a single layer.
While earlier studies have focussed on the transfer of tiny, nanoscale aerosol particles through masks, the researchers from the University of Illinois at Urbana-Champaign in the US said speaking, coughing, and sneezing generates larger droplets -- about one millimeter in diameter -- that can carry virus particles.
They said the larger droplets pose a problem as they can squeeze through the pores of some fabrics if they have sufficient momentum, and break into smaller droplets and become airborne.
In the study, published in the journal Extreme Mechanics Letters, the scientists filled the nozzle of an inhaler with distilled water seeded with easy-to-find ultra small fluorescent particles -- which happens to be the size of a novel coronavirus particle.
The inhaler forced the water through the nozzle when puffed, and generated high-momentum droplets that collected on a plastic dish placed in front of the inhaler, the study noted.
The researchers repeated this process with the various materials placed over the collection dishes to test their ability to block the particles.
"We count the number of nanoparticles landing on the dish using a high-resolution confocal microscope. We can then use the ratio of the number collected with and without the fabric to give us a measure of droplet-blocking efficiency," said study co-author Taher Saif.
However, the scientists said for an individual to feel compelled to wear a mask, the material must not only be able to block the droplets, but also be comfortable and breathable.
"A mask made out of a low-breathability fabric is not only uncomfortable, but can also result in leakage as the exhaled air is forced out around contours of a face, defeating the purpose of the mask and providing a false sense of protection," Saif said.
"Our goal is to show that many common fabrics exploit the trade-off between breathability and efficiency of blocking droplets -- large and small," he added.
The scientists tested the breathability and droplet-blocking ability of 11 common household fabrics, including new and used garments, quilted cloths, bedsheets and dishcloth material, using a medical mask as a benchmark.
They then characterised the fabrics in terms of their construction, fiber content, weight, thread count, porosity and water-absorption rate.
Their analyses revealed that droplets leave the inhaler at about 17 metres per second (mps) while those released by speaking, coughing and sneezing have velocities within the range of 10 to 40 (mps).
"We found that all of the fabrics tested are considerably effective at blocking the 100 nanometer particles carried by high-velocity droplets similar to those that may be released by speaking, coughing and sneezing, even as a single layer," Saif said.
"With two or three layers, even the more permeable fabrics, such as T-shirt cloth, achieve droplet-blocking efficiency that is similar to that of a medical mask, while still maintaining comparable or better breathability," he added.
The researchers believe the new experimental platform may offer a way to test fabrics for their blocking efficiency against the small and larger droplets that are released as people breathe, or cough.
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Inappropriate for MLAs seeking free IPL tickets, says D.K. Suresh
Bengaluru: Bengaluru Milk Union Ltd President D.K. Suresh on Monday said it is inappropriate for MLAs to seek free IPL tickets, adding that those interested in watching matches should pay for them personally.
Speaking to reporters near his residence in Sadashivanagar, he said, “IPL is a commercial tournament and does not represent the country. It is not right for public representatives to focus too much on such matters.”
Referring to the recent controversy during the RCB celebrations, he said, “let us find out who benefited the most from the statements made during the incident.” He also pointed out that BJP MLAs had received IPL tickets as well.
Responding to discussions about relocating the Chinnaswamy Stadium, Suresh said the government has already approved the construction of a new stadium at a location he had proposed.
“I had suggested building a stadium in Surya City and submitted a proposal for it. Bengaluru needs four stadiums in four directions to cater to its growing population and encourage youth participation in sports,” he said.
He noted that apart from Kanteerava Stadium, KSCA, and the Football Stadium, there are limited facilities in the city.
“When I was a Lok Sabha member, I had proposed allocating 100 acres in my constituency at Surya City. The land was later earmarked and the plan approved,” he added.
Suresh said he has discussed the project with Minister Zameer Ahmed Khan, Rajiv Gandhi Housing Corporation Chairman Shivalingegowda, and Anekal MLA Shivanna.
“The Cabinet has now approved the project, and a stadium will be developed on around 50–60 acres,” he said.
He further added that he has requested the Deputy Chief Minister to build another stadium at Shivarama Karanth Layout through the BDA, where 40 acres have been allocated. Plans are also being discussed to develop a well-equipped stadium in Bidadi.
Commending state government's recent bilingual policy move, Suresh said forcing children to learn three languages could affect their comprehension.
“It is a good decision to make two languages compulsory. Learning a third language should be left to the choice of students and parents,” he said.
Responding to criticism from BJP leaders, he said their tendency is to oppose every decision of the government.
“To please their central leadership, they take a pro-Hindi stance. Instead, they should advocate for the adoption of Kannada in all states,” he said.
When asked about the earlier three-language policy under Congress, he said, “the situation is different now. Today, the focus should be on quality learning. Kannada should remain the primary language, while students and parents can choose an additional language.”
