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Back to school: University of Cambridge online tool shows how ventilation reduces risk of Covid-19 transmission in classrooms

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With pupils heading back in classrooms from March 8, a new tool created by Cambridge University researchers could help show schools how to reduce the risk of infections in classrooms.

The scientists have built the tool Airborne.cam to show the impact of wearing masks, opening windows and taking more break times on reducing the amount of Covid-19 virus in the air.

Distancing, masks and ventilation can reduce transmission of Covid-19
Distancing, masks and ventilation can reduce transmission of Covid-19

The results, reported in the journal Proceedings of the Royal Society A, show that social distancing measures alone do not provide adequate protection from the virus.

The researchers, from the University of Cambridge and Imperial College London, used mathematical models to show how SARS-CoV-2 – the virus which causes Covid-19 – spreads in different indoor spaces depending on the size, occupancy, ventilation and whether masks are being worn.

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 that risk changes over time.

The scientific consensus is that the vast majority of Covid-19 cases are spread through indoor transmission. With schools returning next week, the tool could help school leaders work out exactly what risks children and teachers are facing and what they can do to make classrooms safer.

Dr Pedro de Oliveira, from Cambridge’s Department of Engineering, and the paper’s first author, said: “In a school environment, to be safe you would need to make sure that the rooms are not crowded and you have enough ventilation and the children are a safe different distance from each other.

Opening windows could help reduce the spread of Covid-19 at school
Opening windows could help reduce the spread of Covid-19 at school

“Using our tool, you can understand, on top of following the government regulations, how you can improve your indoor conditions. You can see the effect that different grades of mask will have on the risk of infection and the relative reduction in risk you can make with ventilation and occupancy.

“You can see what the effect will be if you increase the ventilation rate and that by taking breaks throughout the day when no one is in the room this can also impact the risk of infection.”

The tool allows users to type in the room size, number of people inside, what type of mask they are wearing, the amount of fresh air coming in and the amount of time the room will be empty during the day. For those answers it provides a percentage risk of catching the virus from one infected person in the room. Dr Oliviera said the university was already using this tool to assess whether lecture spaces and seminar rooms had enough ventilation.

The latest government guidance is that all secondary school children, apart from those with exemptions, should wear masks in classrooms if they are not able to be more than two metres distant from the next student.

However, Claire Coates, principal of Cambourne Village College, said: “The biggest misunderstanding – students are not socially distanced in class. They are packed in more closely than usual because you have to have a two -metre safe zone at the front of the class behind which the teacher stays. If you’ve got a typical square classroom of 55 square metres with 32 children in it, those rows are pushed further back to give that extra clearance at the front so the kids are actually closer together in class than they would have been. And they are sitting two to a table, shoulder to shoulder.”

She said it would be easier to keep students at a safer distance if schools returned on a rota system.

“If schools had been given some sort of flexibility, we could have increased the social distancing in school. But that’s not the case and that also puts a lot of pressure on schools to be making individual decisions and makes it logistically potentially even harder.”

Secondary school pupils will be asked to wear masks
Secondary school pupils will be asked to wear masks

Another school trust is concerned about how students will be kept in their bubbles during lunch times.

Stephen Munday, chief executive of CAM Academy Trust, said: “What do you do about social spaces? How do you serve lunch? Where do they go? In our secondaries and depending on the weather, we’ll see if we need to hire marquees, which we did before, to create more spaces so groups can have somewhere to go outside of lessons where they can socialise in their bubbles and with protocols in place.”

The trust is looking at getting meals delivered to particular areas of the school to limit movement or creating ready-to-go meals students can collect and take to a designated eating area.

Cambridgeshire County Council’s director of education Jonathan Lewis says he has given ventilation advice to schools: “What we’re stepping into here is exactly the same as what we’ve stepped into in September. The outbreak of Covid cases in school has been really low relative to the amount of people we’ve got going in there.

“There are risk assessments, there is advice and guidance – we’ve given out information on ventilation, cleaning, you name it.”

See the tool at Airborne.cam.

Additional reporting: Gemma Gardner

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