A breath of fresh air in the classroom

How CO2 detectors can help you manage your institution’s ventilation – and prevent Covid-19 transmission

Millions of pupils and staff shivered through the spring of 2021 with windows flung open to ventilate classrooms regardless of the chill. Ventilation is the latest weapon in attempts to mitigate the spread of Covid-19 as the spotlight turns on air quality. But what if there were a more scientific way to monitor the air quality in classrooms than flinging open the windows and hoping for the best?

Since the pandemic began in 2020 we have all had to become something of an expert in areas of science that were previously mysterious to us: virology, immunology, epidemiology. The latest area to come under scrutiny is air quality in relation to the spread of the virus. In the early days of the pandemic, experts believed that the virus largely spread on surfaces. But now the evidence shows that it is airborne and people breathe the virus in and out.

In days gone by, our mothers would start their spring cleaning ritual by flinging open the windows to give the house a good airing. And it seems the idea of improving and monitoring the quality of air and ventilation may be due a comeback. In other countries the idea of airing and air quality is much more prevalent. In Germany for example, airing the house daily, often by opening all the windows to allow for cross ventilation, is commonplace, and there is a raft of words to describe the different types of airing.

Of course, the thinking on air quality has become more focused given the information that the coronavirus is an airborne infection. It is acknowledged now that the main way of spreading Covid-19 is through contact with an infected person. When someone with Covid-19 breathes, speaks, coughs or sneezes, they release particles – droplets and aerosols – containing the virus that cause Covid-19. These particles can then be breathed in by another person.

Plenty of recent research shows that there is clear evidence that air quality correlates with the number of sick days taken, and schools without any mechanical ventilation are being encouraged to keep classroom windows open to improve air quality. Computer simulations show how easily the air in a poorly ventilated room can become hazardous and airing classrooms was added to mask-wearing, handwashing and social distancing in the list of measures that we should take to help stop the spread of the virus.

CO2 is generated in air exhaled by people which can become more concentrated indoors in poorly ventilated spaces like classrooms. Each person will exhale approximately eight litres of air per minute at a concentration around 40,000 parts per million (ppm), and that air has obviously been in close contact with their lung tissue. The air they exhale also contains tiny liquid droplets which, due to their small size, can remain floating in the air for some time. This makes it obvious why the virus can spread through the air, and why we have been asked to wear masks in public indoor spaces.

If you’re indoors, in a poorly ventilated room for a long time, then you’re at quite a high risk

If there is a high amount of exhaled CO2 in the air, there is also a high number of aerosols. A high concentration of aerosol increases the risk of infection for everyone else in the room.
That is why scientists have earmarked CO2 monitoring as a transmission risk indicator and the Sage Environmental and Modelling Group (EMG) has concluded that measuring elevated levels of carbon dioxide would be an effective way to spot if air flow levels have reached a level where the coronavirus is more likely to spread.

Professor John Wenger, director of the Centre for Research into Atmospheric Chemistry at University College Cork, argues that room level transmission is “the key. It’s in the air, and it can fill a room. The amount of the virus in the air can accumulate, and we get an increased exposure.

“If you’re indoors, in a poorly ventilated room for a long time, then you’re at quite a high risk even if you’re distanced, because the air moves around.”

While the presence of higher levels of CO2 does not, in and of itself, indicate directly where infection exists, it can be a proxy for transmission risk according to the Sage scientists.

“Since the coronavirus is spread through the air, higher CO2 levels in a room likely mean there is a higher chance of transmission if an infected person is inside,” leading aerosol scientist Prof Shelly Miller concludes.

So, it seems that fresh air plays a significant role in keeping the virus at bay indoors. But how is it possible to monitor the air quality in classrooms when most schools do not have any significant mechanical ventilation? Obviously, rooms that feel or smell stuffy, have no opening windows, or have high occupancy would be obvious places to start. But continuously monitoring air quality throughout a school could prove more difficult.

Fortunately, reliable, easy-to-use, and affordable domestic CO2 detectors are now available.

The new ABUS Airsecure CO2 detector reliably warns when CO2 concentrations are reaching a level where extra ventilation is required. It also measures temperature and humidity giving a reliable real-time indicator of air quality. It can be placed anywhere, on a wall mounting or simply standalone. It runs on mains power but has a battery back up, so it is never off-duty. Scientists believe that, aside for infection risk, using a CO2 monitor could reduce headaches, nausea, and tiredness as we learn to control the air quality in the classrooms where we are all going to be spending so much more time.


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