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Melbourne, Jul 24: Home-made cloth face masks may need a minimum of two layers, and preferably three, to prevent the dispersal of viral droplets associated with Covid-19, according to a study.

Researchers, including those from the University of New South Wales in Australia, noted that viral droplets are generated by those infected with the novel coronavirus when they cough, sneeze, or speak.

As face masks have been proven to protect healthy people from inhaling infectious droplets as well as reducing the spread from those who are already infected, several types of material have been suggested for these, but based on little or no evidence of how well they work, the scientists said.

In the current study, published in the journal Thorax, the researchers compared the effectiveness of single and double-layer cloth face coverings with a surgical face mask (Bao Thach) at reducing droplet spread.

They said the single layer covering was made from a folded piece of cotton T shirt and hair ties, and the double layer covering was made using the sew method described by the US Centers for Disease Control and Prevention (CDC).

The scientists used a tailored LED lighting system and a high-speed camera to film the dispersal of airborne droplets produced by a healthy person with no respiratory infection, during speaking, coughing, and sneezing while wearing each type of mask.

Their analysis showed that the surgical face mask was the most effective at reducing airborne droplet dispersal, although even a single layer cloth face covering reduced the droplet spread from speaking.

But the study noted that a double layer covering was better than a single layer in reducing the droplet spread from coughing and sneezing.

According to the researchers, the effectiveness of cloth face masks is dependent on the number of layers of the covering, the type of material used, design, fit as well as the frequency of washing.

Based on their observations, they said a home made cloth mask with at least two layers is preferable to a single layer mask.

"Guidelines on home-made cloth masks should stipulate multiple layers," the scientists said, adding that there is a need for more research to inform safer cloth mask design.

New Delhi, Jun 29: Witnessing azure skies and breathable air for the last three months, Delhi on Monday recorded deterioration in its air quality, with particulate matter with diameter of 2.5 and 10 microns -- too small to be filtered out of the human body -- standing at 52 and 297 micrograms per cubic respectively.

Gufran Beig, Project Director of System of Air Quality Weather Forecasting and Research (SAFAR), said that the sudden spike in air pollution is due to a mild dust storm blowing from Rajasthan.

"Since the wind direction is changing and moist air is coming in, the air quality in Delhi will become better by tomorrow," Beig told IANS.

Central Pollution Control Board (CPCB) data showed that the overall air quality near Delhi Technical University (DTU) area stood at 326 micrograms per cubic, followed by 308 at Narela and 307 at Mundka.

Out of 36 stations, the AQI in as many as 30 stations was above 200 micrograms per cubic till 1 pm on Monday.

The System of Air Quality Weather Forecasting and Research categorises air quality in the 0-50 range as good, 51-100 as satisfactory, 101-200 as moderate, 201-300 as poor, 301-400 as very poor, and above 400 as severe.

According to SAFAR's website, "PM 10 (coarser dust particle) is the lead pollutant. AQI is likely to improve to moderate category by tomorrow, and further improvement is expected by July 1."

Researchers indicated that PM 10 and PM 2.5 will be 170 and 47 micrograms per cubic on Tuesday.

With no vehicles plying on the roads or industries shut due to the lockdown since March 25, Delhi's air quality had improved drastically.

According to a study conducted by the Indian Institute of Technology (IIT), Delhi, if the low levels of air pollution reached during the lockdown period are maintained, India's annual death toll could reduce by 6.5 lakh.

Citing the current dismal aviation scenario, Air India is terminating the services of trainee cabin crew and cabin crew by withdrawing the offer of employment of those who were under training.

As per sources, the new crew and trainee pilots might reduce contracts from five years to one year. Sources said Air India is terminating 1,200 crew and employees who are more than 55-yr-old including 190 trainee pilots.

In a letter reviewed by IANS, Air India has informed an applicant who had been selected as cabin crew in August 2019 subject to successful completion of training.

"On behalf of Air India we would like to thank you for the interest shown by you in joining our organization. However, in view of the current aviation scenario, it would not be possible for Air India to impart any further training to you for engaging your services," the company said.

"In view of the above reasons, which are beyond the control of the company, it has been decided to discontinue your training arrangements and dispense with the offer of engagement with immediate effect. The bank guarantee furnished by you at the time of joining is returned herewith," Air India told the cabin crew.

"Once again on behalf of Air India we thank you for your cooperation and trust that you will appreciate the circumstances under which we are constrained to discontinue the training arrangements," the carrier said.