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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India calls for UNSC expansion, says lack of reform 'constrains' global body
New Delhi (PTI): India on Friday strongly called for expansion of the UN Security Council with External Affairs Minister S Jaishankar saying that the effectiveness and credibility of the global body will remain "constrained" without reforming it.
Jaishankar made the remarks at a conclave of the foreign ministers of the BRICS nations in New Delhi.
"We meet at a time when the effectiveness of global governance and the credibility of multilateralism are under increasing scrutiny," he said.
"The world today is more interconnected, complex, and multipolar than when many of our current institutions were created. Yet, the structures that underpin global governance have not kept pace with these changes," he noted.
Jaishankar listed four specific points to press for reforming the key international bodies and multilateral trading systems, and asserted that the reform of the United Nations and its subsidiary bodies remains "central".
"The membership of the United Nations has expanded significantly, and its responsibilities have grown. Yet, key structures, particularly the Security Council, continue to reflect an earlier era," he said.
"Without meaningful reform, including expansion in both permanent and non-permanent categories, the effectiveness and credibility of the UN will remain constrained. Representation of Asia, Africa, and Latin America is essential," he noted.
India has been a strong contender for a permanent seat at the UN Security Council.
Elaborating his second point, Jaishankar said the time has come for serious negotiations for reform of the UN Security Council.
"BRICS itself has debated this issue deeply, especially at the Johannesburg Summit. Our outcome documents have reflected that consensus. But much more has to be done to make reform a reality," he said.
"Third, there is an urgent need to reform the international financial architecture," the external affairs minister said.
He said there is a need to reform the global financial architecture to effectively deal with various economic challenges including vulnerabilities in supply chains, pressures on food and energy security, and inequalities in accessing critical resources.
"Fourth, the multilateral trading system must be strengthened and reformed. Non-market practices, concentration of supply chains, and uncertain market access have exposed the global economy to new risks," he said.
Jaishankar said a rules-based, fair, open, and inclusive trading system, with the World Trade Organisation at its core, remains essential.
"At the same time, it must address asymmetries and reflect the concerns of developing countries," he said.
