Free interactive tool reveals the risk of catching coronavirus indoors

A website built by the University of Cambridge has been created to reveal the risk of infection from coronavirus in indoor spaces. 

The app has various customisable settings which include level of ventilation, number of occupants and the level of activity and mask wearing. 

Anyone can use it to find out the level of risk they are taking while in a room of virtually any size or type.

For each set of parameters the site produces a graph showing the chance of infection over a set period of time, with the default being 9am to 5pm.  

The site is called Airborne.cam and can be accessed here.   

The online tool shows that in an office of 30 people which is 100 square metres with three metre high ceilings, the risk of a person catching the virus from 9am to 5pm if one person is infected and nobody is wearing masks is 6.06 per cent (pictured)

The graph it creates showing an individual’s risk of infection is calculated by a series of scientific equations described in a new study published in Proceedings of the Royal Society A.

Users can determine the room’s occupancy, mask type and activity level. Mask settings include no mask, surgical masks, N95 masks or coverings made of cloth. 

Activity level can also be altered, from sitting/breathing through to heavy exercise. 

Ventilation can also be altered, with six options ranging from poorly ventilated through to the industrial ventilation of hospitals. 

The academics have also built in room dimensions and a time period which is factored into the equation. 

As part of their research the scientists found that two people chatting freely in a poorly-ventilated space while not wearing a mask poses a larger risk of infection than if one of them was to cough. 

In the same office and with consistent settings, if everyone wears a surgical face mask all day and takes an hour lunch break outside, this drops to just 2.13 per cent (pictured)

Pictured, the various settings which can be altered by users to calculate a specific level of individual risk for a space via the Airborne.cam website 

This, they say, is because speaking leads to exhalation of small droplets called aerosols which float around a confined space. 

Without adequate ventilation they can linger in the air, increasing the risk a person will inhale them and subsequently get infected. 

However, a cough produces large droplets which are much heavier and likely to plummet to the nearest surface and not stay suspended in the air. 

‘Our knowledge of airborne transmission of SARS-CoV-2 has evolved at an incredible pace, when you consider that it’s been just a year since the virus was identified,’ said Dr Pedro de Oliveira the paper’s first author. 

‘There are different ways to approach this problem. In our work, we consider the wide range of respiratory droplets humans exhale to demonstrate different scenarios of airborne viral transmission – the first being the quick spread of small infectious droplets over several metres in a matter of a few seconds, which can happen both indoors and outdoors. 

‘Then, we show how these small droplets can accumulate in indoor spaces in the long term, and how this can be mitigated with adequate ventilation.’ 

The free online tool shows that in an office of 30 people which is 100 square metres (1,076 square feet) with three metre (9.8ft) high ceilings, the risk of a person catching the virus from 9am to 5pm if one person is infected and nobody is wearing masks is 6.06 per cent. 

If everyone in the office wears a surgical face mask all day and takes an hour lunch break outside, this drops to just 2.13 per cent. 

But if three people are working in a an average-sized dining room (18 sq metres/193 square feet) that has poor ventilation, and one person is infected, the risk of catching the virus over eight hours is 48.73 per cent. 

The calculations are based on the assumption that ‘hands are washed and that individuals are far apart from each other — i.e. there is no risk of short-range transmission by droplets/aerosol’.

The tool is now being actively used by the University of Cambridge which has made it a prerequisite for high-risk spaces at the institution which will allow staff to put in mitigating factors, such as reduced capacity or increased ventilation. 

‘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,’ said co-author Savvas Gkantonas, who led the development of the app with Dr de Oliveira. 

A similar tool was previously created by researchers across the Atlantic Ocean at MIT. 

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. 

In a standard room with 8ft tall ceilings and each wall measuring around 15ft long, 10 fit young people all diligently wearing surgical face masks could safely sit there talking normally for two hours if the windows were shut due to the cold temperatures outside.

But, for a family of ten, of which some are elderly, in a standard dining room for dinner where nobody is wearing a mask because they are eating and the windows are closed because it is cold outside – and there’s a few heated discussions with raised voices – the tool reveals the safe limit is slashed to just three minutes. 

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. 

The MIT tool’s settings for homes, school’s and restaurants suggest that a couple of people in any are likely safe for days in a home with more space, or hours in a restaurant – but once the rooms are more densely occupied, the risk goes up