Covid: how can schools improve air quality to reduce transmission? | Schools

Pupils will return to school in England, Wales and Northern Ireland this week amid warnings from experts that the restart could fuel a surge in Covid cases. We take a look at measures that could improve air quality in schools and reduce transmission.

Carbon dioxide (CO₂) monitors

We breathe out CO2, meaning higher levels of the gas are found in crowded rooms with poor ventilation. CO₂ monitors do not change air quality, but are a cheap, effective canary in the coalmine.

Experts have noted their limitations, particularly in spaces of low occupancy or large volume.

However, Sage member Catherine Noakes, professor of environmental engineering for buildings at the University of Leeds, speaking in a personal capacity, said classrooms were a good setting for CO₂ monitors. “Their spaces are about the right size [and] they’ve got a regular occupancy,” she said.

Opening windows

“Many school classrooms will just have opening windows [for ventilation], although certainly, over the last 10 to 15 years, there have been more schools with additional equipment,” said Dr Shaun Fitzgerald, an expert in ventilation from the University of Cambridge.

Noakes added that making sure windows can open “is probably the most viable short-term option” for schools.

Opening windows all the way can quickly make a room cold in winter, but the amount they need to be open to improve ventilation depends upon the wind speed and the temperature difference between outdoors and indoors.

“In colder weather, opening the window a small amount can result in ventilation that is almost as effective as opening the window fully in the summer,” the Environmental Modelling Group (EMG) of Sage has written.

Noakes has tweeted a range of tricks for improving ventilation by opening windows. “For winter ventilation, it’s a good idea to open windows that are high-level,” she said. “Because then the cold air comes in above everybody’s heads and has a chance to mix with the warmer air, rather than give you a really cold [draught] in the space where you’re sitting.”

If high-level windows are absent, then heat exchangers or fans to mix the incoming cold air with the warm room air may be needed, Fitzgerald said. Noakes said many CO₂ monitors also measure temperature, which can tell teachers they can “afford to shut the windows” when “your CO₂ is really low and your temperature is also really low”.

Ozone disinfecting machines

While some studies have suggested ozone is effective at deactivating the coronavirus, it is an environmental pollutant and can cause irritation and damage to airways. What’s more, people need to be trained in the safe use of the machines.

“The challenge with ozone disinfection is you cannot use it in an occupied space,” said Noakes, adding that the process can take about two to five hours.

“To be honest, you’d probably only do that if you’ve got an outbreak. You wouldn’t do it routinely every day,” she said, noting that its benefits might prove limited since, even in poorly ventilated rooms, the virus will have disappeared from the air overnight.

“I’m a bit sceptical that they can replace standard cleaning,” Noakes added, echoing concerns from the Health and Safety Executive.

Air conditioning

Mechanical ventilation units are good, said Noakes, as they bring in fresh air. However, those that recirculate air may make things worse.

“People think that they’re comfortable, so they think the room’s well ventilated, and it’s not,” she said.

Air cleaners

There are many air-cleaning products on the market, although Noakes said evidence on their effectiveness is patchy. One option is an ultraviolet cleaning device, although the best ones can be complicated to design and install.

Another option is an air filter – basically a box containing a fan and very fine HEPA filters. Air is drawn through the device, and viruses and other contaminants are removed.

However, they can be noisy, it is important to pick the right size, and they cost about £200-£500 a unit.

“You probably need at least two per classroom,” said Noakes, adding it is better to first identify where ventilation might need improvement but windows cannot not be opened.