The tool reveals that the types of masks people are wearing, and the ventilation system can dramatically drive risks up or down

Outdoor spaces are safer than indoor ones for catching coronavirus, and more people pose a greater risk than smaller groups, public health officials frequently remind amid the pandemic. But a new online tool can help you nail down just how likely to you are to catch coronavirus if someone in the home, office or school is infected.

Massachusetts Institutes of Technology researchers have turned their complex mathematical equation to work out the risk of catching the coronavirus if one person in a room is infected Covid-19 into a handy interactive.

Anyone can use it to find out how long it’s safe to stay in a room of virtually any size or type, with anywhere from one to 100 people if one of them has the virus.

The tool reveals that the size or type of the room doesn’t matter all that much – but what types of masks the people occupying it are wearing, and the ventilation system it’s equipped with can dramatically drive risks up or down.

Its developers say the online site allows people to calculate risk with more nuance than the simple, and often vague, guidance to form ‘bubbles’ or socially distance.

Calculations which inform the site were published by authors John Bush and Martin Bazant on the pe-print server medRxiv.

MIT scientists used fluid dynamics – or how infectious droplets might float around a room – to calculate the risks of these exposures over a given period of time. However, the tool is currently only equipped to calculate based on one infected person in a room, not several.

This makes it useful for small gatherings, but in larger places where there may be dozens of people, for example at a supermarket, the application becomes unusable.

However, people can visualise the impact of what their household Covid protocols can do.

But dropping the mask to below their chin just 50 per cent of the time sees this figure drop to four minutes.

While parameters of the room and mitigating aspects are important, the researchers say, the most critical impactor is human behaviour. Specifically, the wearing of high-quality face masks.

In their study, the researchers applied their work to two case studies which have both garnered huge scrutiny over their role in spreading the disease: classrooms and care homes.