04-02-2020, 12:17 PM
https://www.bbc.com/news/science-environment-52126735
The WHO recommends keeping a distance of at least 1m from anyone coughing or sneezing to avoid the risk of infection. It says people who are sick and show symptoms should wear masks. But it advises that healthy people only need to wear them if they are caring for others suspected of being infected or if they themselves are coughing or sneezing. It emphasises that masks are only effective if combined with frequent hand-washing and used and disposed of properly.
The UK, along with other countries including the US, advises that social distancing should mean staying at least 2m apart. This advice is based on evidence showing that viruses can only be transmitted while carried within drops of liquid. The understanding is that most of those drops will either evaporate or fall to the ground near to the person who released them.
Researchers at the Massachusetts Institute of Technology in Cambridge, US, used high-speed cameras and other sensors to assess precisely what happens after a cough or sneeze. They found that an exhalation generates a small fast-moving cloud of gas that can contain droplets of liquid of varying sizes and that the smallest of these can be carried in the cloud over long distances. The study conducted in laboratory conditions found that coughs can project liquid up to 6m away and that sneezes, which involve much higher speeds, can reach up to 8m away. The scientist who led the study, Prof Lydia Bourouiba of MIT, is concerned about the current concept of "safe distances". "What we exhale, cough or sneeze is a gas cloud that has high momentum that can go far, traps the drops of all sizes in it and carries them through the room," she said. "So having this false idea of safety at one to two metres, which somehow drops will just fall to the ground at that distance is not based on what we have quantified, measured and visualised directly."
Prof Bourouiba's view is that in certain situations, especially indoors in poorly ventilated rooms, wearing masks would reduce the risks. For example, when facing someone who's infected, masks could help divert the flow of their breath and its load of virus away from your mouth. Flimsy masks are not going to protect from inhaling the smallest particulates in the air because they do not provide filtration, but they would potentially divert the cloud that is being emitted with high momentum to the side instead of forward. He said that if the evidence is supported, then "it might be that wearing a mask is equally as effective or more effective than distancing." He adds a warning that masks need to be worn properly, with a seal over the nose. If they become moist, then particles can pass through. People must remove them carefully to avoid their hands becoming contaminated. He also adds that masks need to be worn consistently. "It's not on to wear a mask and then decide to take it off to smoke a cigarette or eat a meal - it must be worn full time," he said.
A spokesperson for Public Health England said there was little evidence of widespread benefit from wearing masks outside clinical settings. Facemasks must be worn correctly, changed frequently, removed properly, disposed of safely and used in combination with good universal hygiene behaviour in order for them to be effective.
The WHO recommends keeping a distance of at least 1m from anyone coughing or sneezing to avoid the risk of infection. It says people who are sick and show symptoms should wear masks. But it advises that healthy people only need to wear them if they are caring for others suspected of being infected or if they themselves are coughing or sneezing. It emphasises that masks are only effective if combined with frequent hand-washing and used and disposed of properly.
The UK, along with other countries including the US, advises that social distancing should mean staying at least 2m apart. This advice is based on evidence showing that viruses can only be transmitted while carried within drops of liquid. The understanding is that most of those drops will either evaporate or fall to the ground near to the person who released them.
Researchers at the Massachusetts Institute of Technology in Cambridge, US, used high-speed cameras and other sensors to assess precisely what happens after a cough or sneeze. They found that an exhalation generates a small fast-moving cloud of gas that can contain droplets of liquid of varying sizes and that the smallest of these can be carried in the cloud over long distances. The study conducted in laboratory conditions found that coughs can project liquid up to 6m away and that sneezes, which involve much higher speeds, can reach up to 8m away. The scientist who led the study, Prof Lydia Bourouiba of MIT, is concerned about the current concept of "safe distances". "What we exhale, cough or sneeze is a gas cloud that has high momentum that can go far, traps the drops of all sizes in it and carries them through the room," she said. "So having this false idea of safety at one to two metres, which somehow drops will just fall to the ground at that distance is not based on what we have quantified, measured and visualised directly."
Prof Bourouiba's view is that in certain situations, especially indoors in poorly ventilated rooms, wearing masks would reduce the risks. For example, when facing someone who's infected, masks could help divert the flow of their breath and its load of virus away from your mouth. Flimsy masks are not going to protect from inhaling the smallest particulates in the air because they do not provide filtration, but they would potentially divert the cloud that is being emitted with high momentum to the side instead of forward. He said that if the evidence is supported, then "it might be that wearing a mask is equally as effective or more effective than distancing." He adds a warning that masks need to be worn properly, with a seal over the nose. If they become moist, then particles can pass through. People must remove them carefully to avoid their hands becoming contaminated. He also adds that masks need to be worn consistently. "It's not on to wear a mask and then decide to take it off to smoke a cigarette or eat a meal - it must be worn full time," he said.
A spokesperson for Public Health England said there was little evidence of widespread benefit from wearing masks outside clinical settings. Facemasks must be worn correctly, changed frequently, removed properly, disposed of safely and used in combination with good universal hygiene behaviour in order for them to be effective.