Online app

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

The essential role of ventilation in the spread of COVID-19[female[feminine was quantified by researchers, who found that in poorly ventilated spaces, the virus spreads over two meters in seconds and is much more likely to be spread through prolonged conversation than coughing.

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

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

Researchers have found that when two people are in a poorly ventilated space and neither is wearing a mask, prolonged conversation is much more likely to spread the virus than a short cough. When we speak, we exhale smaller droplets, or aerosols, which easily spread around a room and accumulate if ventilation is not adequate. In contrast, a cough expels more large droplets, which are more likely to settle on surfaces after they are emitted.

It only takes a few seconds for aerosols to spread over two meters when masks are not worn, implying that physical distancing in the absence of ventilation is not sufficient to ensure safety for long periods of time. exposure. However, when masks of any kind are worn, they slow down the momentum of breathing and filter out some of the exhaled droplets, in turn reducing 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 transmission indoors, whether through 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 cases. -19.

“Our knowledge of airborne transmission of SARS-CoV-2 has evolved at an incredible rate, considering that it has only been a year since the virus was first identified,” said Dr Pedro de Oliveira of the department. of Cambridge Engineering, and the first author’s article. “There are different ways of approaching 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 being the rapid spread of small infectious droplets over several meters in seconds, which can occur at both inside and out. outside. Next, we show how these tiny droplets can accumulate in indoor spaces over the long term, and how this can be mitigated with proper ventilation.

The researchers used mathematical models to calculate the amount of virus in exhaled particles and to determine how the particles evaporate and settle on surfaces. In addition, they used characteristics of the virus, such as its decay rate and viral load in infected people, to estimate the risk of transmission in an indoor environment due to normal speech or a short cough. ‘an infectious person. For example, they show that the risk of infection after speaking for an hour in a typical conference room was high, but the risk could be significantly reduced with adequate ventilation.

Based on their models, the researchers have now built, 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 tool is already in use in several academic departments at the University of Cambridge. The tool is now a requirement for all high-risk spaces at the University, allowing departments to easily identify hazards and changes in control measures needed to ensure aerosols do not become a health risk.

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

“We look at all aspects of aerosol and droplet transmission to understand, for example, the fluid mechanics involved in coughing and speech,” said lead author Prof. Epaminondas Mastorakos, also from the department of engineering. “The role of turbulence and how it affects droplets that settle by gravity and those that stay afloat in air, in particular, is not well understood. We hope these and other new findings will be implemented as safety factors in the app as we continue our research. “

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

Reference: “Evolution of spray and aerosol from respiratory releases: Theory estimate for insight on viral transmission” by PM de Oliveira, LCC Mesquita, S. Gkantonas, A. Giusti and E. Mastorakos January 20, 2021, Proceedings of the Royal Society A.
DOI: 10.1098 / rspa.2020.0584

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