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High CO2 Levels and Poor Ventilation Raise Concerns for Children’s Health and COVID Risk

In Scotland, parents and politicians alike are calling for air filters to improve school ventilation – as classrooms show higher than recommended levels of CO2, Sian Norris reports

Children wash their hands on the first day back at school after lockdown. Photo: Danny Lawson/PA/Alamy

High CO2 Levels and Poor Ventilation Raise Concerns for Children’s Health and COVID Risk

In Scotland, parents and politicians alike are calling for air filters to improve school ventilation – as classrooms show higher than recommended levels of CO2

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As children pack their schoolbags and head back to lessons after Easter, parents have expressed concern that pupils in Edinburgh are studying in classrooms where CO2 levels exceed recommended safety limits – and are therefore at risk of COVID-19 transmission, Byline Times can reveal. 

Scottish Government guidance states that CO2 concentrations in most classrooms should not exceed 1,500 parts per million (ppm) – reduced to 800ppm in music classrooms and gyms. 

The UK maximum is higher than other countries, some of which recommend 800ppm. The Lancet has published a study finding that schools are “chronically under-ventilated”, impacting children’s health and concentration.

A report commissioned by Edinburgh City Council, and undertaken by Edinburgh Napier University – titled ‘COVID-19 Mitigation In Schools’ – found that some classrooms had CO2 levels as high as 2,810ppm, while one music room had concentrations of 1,990ppm. 

The research took place between November 2020 and February 2021 across nine out of 123 primary schools. More widely, the Scottish Government asked local authorities across the country to assess CO2 concentrations in learning, teaching and play spaces. 

The report concluded that “from the data presented… most of the schools monitored demonstrated periods where the maximum recorded CO2 concentrations exceeded threshold values identified”, with the exception of two schools. 

All the rooms in one school had levels between 1,863 and 2,810ppm. In a second school, all but one room had levels between 1,560 and 1,862ppm, while a third school had three classrooms where the levels were 2,001ppm, 1,620ppm and 1,999ppm respectively.


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Edinburgh City Council confirmed that it has purchased portable CO2 monitors for all its schools and “is currently working on a programme to install fixed CO2 sensors across all learning and teaching spaces in schools”.

The concern is that while schools with CO2 monitors can now tell if levels are too high in the classroom, they have few options to reduce levels. The report noted that “leaving the window open all the time, even when no pupils are inside, helps keep the levels down, but is insufficient when the number of pupils in a classroom is too great”.

A local authority worker and trade union activist, who wished to remain anonymous, told Byline Times that there are “nowhere near enough CO2 monitors in schools” and the recommended responses to when levels are too high are not being followed. 

“We need to do more to protect people,” they said. “Local authorities are following the guidance, but we are still seeing outbreaks even when guidance is being followed, as it doesn’t go far enough.”

They confirmed that COVID-19 rates remain high in Edinburgh’s schools. A Freedom of Information request found that, between 21 October and 6 December last year, 3,097 pupils tested positive for the Coronavirus.

A council spokesperson told Byline Times: “The monitoring did identify the maximum CO2 levels in some classrooms exceeded the 1,500ppm upper limit and recommendations were made, including raising awareness of the importance of ventilations in classrooms, and giving guidance on the best strategies for ventilating spaces. Training and revised guidance was subsequently provided to school staff.”

The Fight for HEPA Air Filters

One Edinburgh parent, Sam Gajewski, has been advocating for schools to install HEPA Air Filters to reduce CO2 concentrations and therefore COVID-19 transmission.

More than one academic study has recommended a combination of “dilution methods” – such as opening windows – alongside “filtration methods” – such as air filters – to reduce COVID-19 transmission. A 2020 study found that “ventilation strategies associated with lower school incidence included dilution methods alone (35% lower incidence) or in combination with filtration methods (48% lower incidence)”. 

However, despite the growing body of evidence, Gajewski’s efforts have been met with resistance – with schools, local authorities and the Scottish and Westminster Governments promoting ventilation via open windows, instead of filters alongside open windows. 

In email correspondence seen by Byline Times, Gajewski’s school assures him that the Scottish’s Government’s guidance is that air filters should only be used in “exceptional circumstances”. The Health and Safety Executive states that “air cleaning or filtration is not a substitute for good ventilation, but where poor ventilation cannot be improved, these systems can reduce airborne Coronavirus in a space”. 

A spokesperson for the Scottish Government told Byline Times that “expert advice is clear that air cleaning devices should not be used as a substitute for ventilation”. 

But Gajewski considers this a form of ‘gaslighting’ as it ignores that no one is calling for filters to replace natural ventilation. Instead, he and a range of MSPs are arguing for a combined approach.

Oliver Mundell, Conservative MSP for Dumfriesshire, told the Scottish Parliament: “There is scientific evidence for [filter’s] efficacy and, therefore, we are talking about an addition to what is happening – it is a belt-and-braces approach.”

Byline Times has also seen correspondence between Gajewski and Edinburgh City Council and the Scottish Government’s curriculum unit. In response to an email to the local authority about introducing HEPA air filters into schools, Gajewski was told that the council’s “current approach is to prioritise natural ventilation” and that “there is currently limited evidence that air cleaners are an effective control measure to prevent COVID-19 spread”. 

This is disputed by Gajewski and by Scottish Liberal Democrat leader Willie Rennie who, in a debate on school ventilation, said: “Irish Government’s expert group on ventilation said that stand-alone high-efficiency particulate air filter devices might be useful in reducing airborne transmission in spaces with insufficient ventilation”. Rennie also cited recommendations from Canada and Australia, questioning why filters are “discouraged in this country”.

The letter from the curriculum unit simply pointed to ​​the guidance for schools which “contains a range of mitigations, such as use of face coverings, ventilation and distancing requirements”.

Labour MSPs have raised the issue of air filters in Holyrood, with Michael Marra calling the area of school ventilation “a serious policy failure by the Scottish Government to date” and calling on the Government to “to ensure that local authorities have funding available to install at least two HEPA filters in each classroom in Scotland”. 

Marra pointed out that, in the summer of 2021, Scottish First Minister Nicola Sturgeon “announced there was to be a ventilation inspection programme, backed by £10 million of funding for remedial action”. However, Marra argued that “what happened next was not a ventilation programme but CO2 monitors being installed in some – but far from all – classrooms”.

The local authority worker told Byline Times that they have been campaigning to install HEPA air filters for 18 months, to no avail. “The Government says filters are not efficient but they are used in healthcare settings and they have long-term health benefits when it comes to respiratory disease,” they said. “Opposition MPs and trade unions should be campaigning to bring these in.”

The World Health Organisation has said that HEPA air filters “can be effective in reducing/lowering concentrations of infectious aerosols in a single space” but should not replace natural ventilation. 

A spokesperson from Edinburgh City Council told this newspaper: “The outcomes from the monitoring and subsequent recommendations from Edinburgh Napier University helped inform the council’s ongoing approach to ventilation including highlighting areas for further investigation/action.

“As a direct outcome of this work, the council purchased portable CO2 monitors for all schools to support the return of schools in April 2021. This was in advance of any Scottish Government requirement for CO2 monitoring in schools.”

The monitors, the council explained, are smart and linked to a central cloud-based platform so its teams can monitor the data produced.

A Scottish Government spokesperson told Byline Times: “We have made an additional £5 million available to local authorities to improve ventilation in schools and early years settings. This funding is helping councils to work towards having a CO2 monitor in every learning, teaching and play space. Monitors are either already in place or are awaiting delivery for almost 95% of those spaces and all 32 local authorities have confirmed they will move to a 1:1 ratio before the summer holidays.

“Only a very small percentage of problematic spaces have to date been identified by local authorities as being problematic and remedial action has been, or is being, undertaken by councils.”

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