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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World saw valour, courage of Indian armed forces through Operation Sindoor: President
New Delhi (PTI): President Droupadi Murmu on Wednesday said the world saw the valour of Indian armed forces through Operation Sindoor when they destroyed terror camps on the strength of their own resources and asserted that any terror act will be responded with decisive action.
"India has proved that power can be used with responsibility and wisdom. The world has seen the valour and courage of Indian armed forces through Operation Sindoor," Murmu said in her address to both Houses of Parliament, marking the beginning of the Budget Session.
"Our nation, on the strength of our own resources, destroyed terror camps. My government sent a message that any act of terror will be responded to with resolute and decisive action," the President said, amid thumping of desks by Prime Minister Narendra Modi and other parliamentarians.
Murmu said the suspension of the Indus Water Treaty was part of India's fight against terror.
"We are also working on Mission Sudarshan Chakra to further strengthen national security," the President said, adding that security forces have also taken decisive action against Maoist terror.
Following Operation Sindoor, she said, the trust on Indian defence platforms has increased.
Murmu further said her government was committed to social justice in the country.
In the third term of the government, she said, work is being done to further empower the poor, and social security benefits are available to nearly 95 crore citizens now.
"My government is committed to true social justice," she said, adding that 25 crore Indians moved out of poverty in the last 10 years.
The President also said the government has been successful in tackling corruption and scams, and ensuring proper use of public funds.
"For India, the end of the first 25 years of this century has been filled with several successes, proud achievements and extraordinary experiences. In the last 10-11 years, India has strengthened its foundation in every sector," she said.
Lauding India's celebration of the 350th martyrdom day of the ninth Sikh guru, Guru Tegh Bahadur, and the country's tribute to revered tribal leader and freedom fighter Birsa Munda on his 150th birth anniversary, Murmu said, "when the country remembers the contribution of its ancestors, the new generation gets inspiration, which further speeds up our journey towards Viksit Bharat (Developed India)."
"The country celebrated the 350th Shaheedi Diwas of Sri Guru Tegh Bahadur Ji. During the 150th birth anniversary of Birsa Munda, the entire country paid him tribute and remembered his contribution to the tribal community," the President said.
"The events related to the 150th birth anniversary of Sardar Vallabhbhai Patel further strengthened the sense of Ek Bharat, Shresht Bharat (One India, Best India). The entire country became witness to how Bharat Ratna Bhupen Hazarika's birth anniversary celebrations filled the country with music and a sense of unity," Murmu said.
The President's mention of the Viksit Bharat – Guarantee for Rozgar and Ajeevika Mission (Gramin) (VB-G RAM G) scheme was met with loud protests from the Opposition benches.
Murmu said the VB-G RAM G initiative would provide guarantee for 125 days of work, would stop corruption and leakages, and provide a new impetus to rural development.
The Opposition members raised slogans demanding its rollback, even as the treasury benches thumped their desk in support of the scheme.
The President had to take a brief pause amid opposition cries of "vapas lo" (roll back) against the Act that replaced the Mahatma Gandhi National Rural Employment Guarantee Act (MGNREGA).
The Opposition parties have been demanding withdrawal of the VB-G RAM G Act and restoration of MGNREGA as a rights-based law in its original form, the right to work and the authority of panchayats.
The government has, meanwhile, claimed that the new Act will further strengthen the guarantee for rural employment.
