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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SWR announces special trains for passengers stranded by large-scale IndiGo cancellations
Bengaluru (PTI): The South Western Railway on Saturday announced a series of special trains, in coordination with Central, South Eastern and Southern Railways, to clear stranded passengers following large-scale IndiGo flight cancellations across the country.
The special services will operate between December 6 and 10 on high-demand routes, including Bengaluru–Chennai, Bengaluru–Pune, Yesvantpur–Hazrat Nizamuddin, Shalimar–Yelahanka and Ernakulam–Yelahanka, officials said.
According to an official statement, SWR will run Train No. 06255/06256 between Chennai Egmore and KSR Bengaluru, 06257/06258 between Bengaluru and MGR Chennai Central, 06259/06260 between Yesvantpur and Hazrat Nizamuddin, and 06263/06264 between Bengaluru and Pune.
ALSO READ: Indigo flights chaos: SCR to run special trains to clear passenger rush
Central Railway will operate Train No. 01413/01414 between Pune and Bengaluru, while South Eastern Railway will run Train No. 08073/08074 between Shalimar and Yelahanka. Southern Railway will operate Train No. 06147/06148 between Ernakulam and Yelahanka, the statement said.
Railways has advised passengers to check updated timings on its official channels and arrive early at stations.
For at least five days in a row, IndiGo flight operations have been significantly disrupted, with a large number of cancellations and delays causing hardships to thousands of passengers. In many cases, baggage has been misplaced.
