# This Online Tool Lets You Calculate Your Risk Of COVID-19 Transmission Indoors

New Yorkers riding the subway with masks during the COVID-19 pandemic on Sept 5, 2020. Image credit: CHOONGKY/Shutterstock.com

Indoor stuffy spaces can be prime locations for COVID-19 to spread, but the risk can vary depending on a multitude of factors. To help people gauge this risk, scientists have developed a free online tool that allows you to plug in a few bits of information and see how risky that environment might be.

Say, for example, you want to look at the risk of going to a restaurant. The calculator will allow you to plug in details about the room size, ventilation, number of people, and other parameters to estimate the risk of infection for a person exposed to virus particles in the room.

The new tool, was developed by researchers from the University of Cambridge and Imperial College London from their study published in the journal Proceedings of the Royal Society A, which used mathematical models to understand how SARS-CoV-2, the virus responsible for COVID-19, spreads in different indoor spaces based on the evaporation and settling of droplets emitted by coughing and speaking.

“The tool 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,” co-author Savvas Gkantonas, of the Department of Engineering at Cambridge, said in a statement

It’s widely known that the majority of COVID-19 transmissions occur indoors where ventilation is generally worse than outside. After being expelled by a cough, breathing, or even talking, aerosolized viral particles can quickly spread in the air over several meters in a matter of a few seconds. While most social distancing guidelines generally say to keep a distance of 2 meters (6.5 feet), this might Importantly, the models also suggested that potentially infectious particles can drift more than 2 meters just from speaking.

However, the risk is slashed if the space is well ventilated with open windows and doors, and everyone is wearing face masks. The model emphasizes that masks work by slowing the breath’s momentum and filtering some (albeit not all) of the exhaled droplets

“We’re looking at all sides of aerosol and droplet transmission to understand, for example, the fluid mechanics involved in coughing and speaking,” said senior author Professor Epaminondas Mastorakos, also from Cambridge. “The role of turbulence and how it affects which droplets settle by gravity and which remain afloat in the air is, in particular, not well understood. We hope these and other new results will be implemented as safety factors in the app as we continue to investigate.”

It's worth noting, the online tool comes with the warning: “The indicated risk should be treated with caution.” While it's based on robust evidence, the researchers note the “uncertainties in the background science are too high for an absolute quantification of risk.” As ever, your safest bet is to stay at home, follow the rules, and avoid any public indoor spaces whenever possible.