For sale, masks are seen displayed on a clothesline in the front yard of a Los Angeles home on July 20, 2020.
Chris Delmas | AFP | fake pictures
A homemade cloth face mask probably needs two to three layers to be effective in preventing the spread of the coronavirus, according to an observational study published Thursday in the medical journal Thorax.
Researchers at the University of New South Wales in Australia looked at the effectiveness of single-layer or double-layer cloth face covers in reducing the spread of respiratory drops that pass when an infected person speaks, coughs, or sneezes. They then compared those results with those of a three-layer surgical mask.
The researchers used LED lighting and a high-speed camera to film the dispersion of airborne droplets produced by a healthy person without respiratory infection. The video to talk was captured at 850 frames per second, while the cough and sneezes were captured at 1,000 frames per second due to the higher ejection rates, they said.
A three-layer surgical facial mask was most effective in reducing airborne droplet dispersal, the researchers found after reviewing the images. Single-layer coverage reduced spread of droplets when speaking, although double-layer coverage was better at reducing droplets when coughing and sneezing, the researchers said.
“A fabric covering with at least two layers is preferable to a single layer,” wrote Prateek Bahl of the UNSW School of Mechanical and Manufacturing Engineering, lead author of the study, in the findings. “The guidelines on homemade fabric masks should stipulate multiple layers.”
To be sure, the researchers said that a single-layer facial covering is better than not having a facial covering. In addition, several other factors determine the effectiveness of cloth masks, such as the type of material, the number of layers, the arrangement of the different layers and the frequency of washing, they said.
The single-layer face covering was made from a folded piece of cotton T-shirt and hair bands. The double-layer coating was done using the sewing method shown by the Centers for Disease Control and Prevention. The researchers used tissue paper to simulate the mucous membrane of the nasal cavity and induce a sneeze, according to the study.
The study comes as the Trump administration pressures the public to adopt facial coverage in an attempt to curb the spread of the coronavirus. The United States has the worst outbreak in the world with 4 million cases and at least 143,820 deaths, according to data compiled by Johns Hopkins University.
President Donald Trump’s response to the pandemic has also come under increasing scrutiny. In recent weeks, Trump has downplayed the threat from the virus, linking the increase in new cases to an increase in evidence. However, public health officials and infectious disease experts dispute those claims, saying that the rate of positive cases in the United States, hospitalizations, and deaths remain high in some states.
Trump approved the masks for the first time this week after resisting them for months. The CDC began recommending face masks to the general public in April.
Earlier in the day, Admiral Brett Giroir, assistant secretary of health for the Department of Health and Human Services, told reporters that 90% or more of the public need to wear face shields to slow the spread of the virus.
“If we close the interior bars, we reduce the occupation of restaurants, we have facial covers and hygiene, this is essentially equivalent to closing the entire economy, which means closing elective surgeries and everything else that entails,” he said.
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