Friday , December 4 2020

The face mask test: which ones are best for limiting Covid’s spread? | World news



S.ome fabric surface coverings for sale in supermarkets and high street pharmacies could be giving people a false sense of security by letting the vast majority of large particles pass through them, an investigation by consumer magazine Which? has revealed.

Three of the masks tested by the magazine’s researchers failed to capture 93% of bacterial particles, meaning the mask wearer could breathe or breathe out of these particles.

However, the surface coatings were found to perform best than surgical masks in blocking bacterial particles, preventing more than 99% of them from penetrating the fabric.

Although reusable fabric masks are not intended to block ultra-fine particles such as viruses, they are designed to hold larger respiratory droplets and aerosols that the wearer inhales, coughs or spits out, so can reduce transmission of any virus particles in them.

Mask survey

“With surface dressings now such an important part of daily life they need to not only be durable and comfortable, but also provide effective filtration of harmful particles to keep us and others safe,” said Natalie Hitchins, Which? head of home products and services. “Our results prove that there is a huge difference in quality between reusable masks sold in stores nationwide and online.”

The researchers looked at a range of popular brands and styles of face covers for sale in the UK, testing them for breathability, durability and comfort as well as the ability to filter bacteria.

Bacterial particles were extracted from an aerosol generator and the proportion made by it was measured through the mask fabric. Measuring three micrometers in diameter the bacteria used were about 30 times larger than coronavirus particles, but the results were likely to apply to Covid-19 nonetheless, independent researchers said.

“The likelihood is that if they leave bacteria through, they will also leave a virus through,” said Cath Noakes, professor and specialist in airborne disease transmission at the University of Leeds. “Although much smaller than bacteria, the virus will be contained in respiratory aerosols and droplets, which are larger. We are probably most concerned with aerosols with a diameter of 1-50 microns, so bacteria are a reasonable proxy for the size range that is likely to matter. ”

In a separate study, published at BMJ Open, Eugenia O’Kelly, at Cambridge University, and colleagues, tested the ability of various fabrics, ranging from T-shirts and socks, to jeans and vacuum bags, to capturing the size of a virus. particles, when emitted at high speeds. These high velocities were comparable to the speed of the air inhaled during coughing or heavy breathing.

O’Kelly found that masks made from multiple layers of fabric were more effective, holding 45% of particles, compared to 35% for single-layer fabric masks.

The addition of a layer of fusible non-woven interface – such an iron-forward webbing to a stiffener – added an additional 11% to mask filtration capability, although this does affect breathing.

James Ward, an engineer from Cambridge University, who was also involved in the research, said: “I think when you buy a face cover or mask you want to consider not just price, but balance of multiple things, including filter. , breathing, durability, fit, long-term comfort and safety. Layering of fabrics is a good idea, but you have to consider the compromise between filtration and breathability.

Which one? it awarded Best Buy status to two of the products it tested – NEQI’s reusable face mask (available from Boots and Ocado), and Great British Designer’s Bags of Ethics face covers (available at Asos and John Lewis).

Although these masks did not receive the highest filter scores, they were considered to be comfortable breathing, but the masks that scored five out of five for filtration had low breathing scores.

Breathing is especially important for people who wear glasses because vapor from trapped breath can cause steaming lenses, encouraging people to pull down or remove their masks. “As winter approaches, the air cools, so glasses will steam more easily,” said Ward.

Which one? two masks were awarded the highest score for comfort in wearing glasses – the Asos and AB Mask. He found that the worst performing masks were made of a single layer of fabric, mostly polyester. Although lightweight and breathable, these masks were not as good for particulate filtration.

He also found that filtration of almost all surface coatings improved after being washed at high temperatures, due to the fibers in the fabrics compressing. O’Kelly warned, however, that masks should not be reused indefinitely as repeated washing can degrade the fabrics.


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