For people with Covid19, speaking to others might be just as dangerous as coughing near them, especially in poorly ventilated spaces, a new study has found.
“Speaking is a very important issue that has to be considered because it produces much finer particles [than coughing], and these particles, or aerosol, can be suspended for over an hour in amounts that are sufficient to cause the disease,” Professor Pedro Magalhães de Oliveira, who specializes in fluid mechanics at the University of Cambridge and was involved in the study, told The Guardian.
Published in Proceedings of the Royal Society A, the study found that it takes just a couple of seconds for exhaled particles to travel beyond two metres. Moreover, even one hour after an infected individual had spoken for as little as 30 seconds, the amount of aerosol particles still suspended in the air contained more viral mass than that dispensed through just one cough by an infected individual. The researchers noted that in small spaces that lack ventilation, this may be enough to spread the infection.
However, the researchers noted that since the chance of being infected depends on the amount of aerosols inhaled, the risk of contagion through conversation may be mitigated by adopting standard safety measures. “You need masks, you need distancing, and you need good ventilation so these particles don’t build up in an indoor space and they are safely removed,” Professor de Oliveira added.
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To help individuals assess their risk of becoming infected in indoor settings via coughed or spoken particles the researchers developed a free, open-source online calculator as well.
While viral load varies — first, from person-to-person, and second, through the course of the infection — and therefore, the risk of infection varies, too, the researchers say their findings and calculator can help restaurants, shops, offices, and even schools design strategies to mitigate contagion risk.
“[This] can help people use fluid mechanics to make better choices, and adapt their day-to-day activities and surroundings in order to suppress risk, both for themselves and for others,” Savvas Gkantonas, whose research focuses on computational fluid dynamics at the University of Cambridge, said in a statement.
To arrive at these conclusions, the researchers built mathematical models to account for the size of droplets emitted by infected people when they speak or cough, the viral load such droplets may contain, as well as the mechanisms governing the evaporation or settling of these aerosols.
