Free online app calculates the risk of COVID-19 transmission in indoor spaces

The important role of ventilation in the distribution of COVID-19 was quantified by researchers, who found that the virus spread within seconds in poorly ventilated spaces within two seconds and was much more likely to spread through prolonged talk than through coughing.

The results, reported in the journal Proceedings of the Royal Society A, shows that social distance measures alone do not provide adequate protection against the virus, and further emphasizes the vital importance of ventilation and face masks to slow the spread of COVID-19.

The researchers, from the University of Cambridge and Imperial College London, used mathematical models to show how EARS-CoV-2 – the virus that causes COVID-19 – spreads in different indoor spaces, depending on the size, occupancy, ventilation and or wearing masks. These models are also the basis of a free online tool, Airborne.cam, which helps users understand how ventilation and other measures affect the risk of indoor transmission, and how the risk changes over time.

The researchers found that when two people find themselves in a poorly ventilated space and do not wear a mask, it is more likely that prolonged talk will spread the virus than a short cough. When we talk, we take out smaller drops or aerosols, which easily disperse into a room and accumulate if ventilation is not adequate. In contrast, cough expels more large droplets, which are more likely to settle on surfaces after release.

It only takes a few seconds for aerosols to spread over two meters if masks are not worn, implying that physical distance in the absence of ventilation is not sufficient to provide safety for long exposure times. When masks of any kind are worn, they slow down the momentum of the breath and filter a portion of the exhaled droplets, which in turn reduces the amount of virus in aerosols that can spread through space.

The scientific consensus is that the vast majority of COVID-19 cases are spread by indoor transmission – whether via aerosols or droplets. And as predicted in summer and fall, now that winter has arrived in the northern hemisphere and people are spending more time indoors, there has been a corresponding increase in the number of COVID-19 cases.

“Our knowledge of the transmission of SARS-CoV-2 into the air has developed at an incredible rate, if you think it’s only a year since the virus was identified,” said Dr. Pedro de Oliveira of the Cambridge Department of Engineering, and the article said. first author. ‘There are different ways to approach this problem. In our work, we consider the wide range of respiratory droplets that humans exhale to demonstrate different scenarios of viral transmission through the air – the first is the rapid spread of small infectious droplets over a few meters within a few seconds, occurring inside and inside can happen outside. Then we show how these small droplets can accumulate in indoor spaces in the long run, and how they can be reduced with adequate ventilation. ”

The researchers used mathematical models to calculate the amount of virus contained in exhaled particles, and to determine how it evaporates and precipitates on surfaces. In addition, they used the characteristics of the virus, such as the decay rate and viral load in infected individuals, to estimate the risk of transmission in an indoor environment due to normal speech or a brief cough by an infectious person. They show, for example, that the risk of infection after an hour of conversation in a typical lecture hall was high, but that the risk can be significantly reduced with adequate ventilation.

Based on their models, the researchers built Airborne.cam, a free open source tool that can be used by those who manage public spaces, such as shops, workplaces and classrooms, to determine if ventilation is adequate. The instrument is already used in various academic departments at the University of Cambridge. The instrument is now a requirement for any higher-risk spaces at the University, enabling departments to easily identify hazards and determine the necessary controls to ensure that aerosols cannot become a health risk.

“The tool can help people use fluid mechanics to make better choices and adjust their daily activities and environment to suppress the risk, both for themselves and for others,” said co-author Savvas Gkantonas, who led the development. , said. of the app with Dr de Oliveira.

“We are looking at all sides of aerosol distribution and droplets to understand, for example, the fluid mechanics involved in coughing and talking,” said senior author Professor Epaminondas Mastorakos, also from the Department of Engineering. ‘The role of turbulence and how it affects which droplets fall by gravity and which remain in the air are not well understood. We hope these and other new results will be implemented as security factors in the app as we investigate further. “

The ongoing development of Airborne.cam, which will soon be available for mobile platforms, is supported in part by Cambridge Enterprise and Churchill College.

Reference: January 20, 2021, Proceedings of the Royal Society A.
DOI: 10.1098 / rspa.2020.0584

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