CO2 monitoring guidance: More questions than answers

Written by: Joanna Parry | Published:
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The government’s guidance on ventilation and CO2 monitoring in schools is at odds with both SAGE and HSE advice, says a concerned Joanna Parry

It was a long time coming, but we welcomed the government’s recent announcement to spend £25m on CO2 monitors for schools and colleges in England for the autumn term.

A more proactive approach, which we and others called for, would have seen these devices put into schools months ago. The government should also have announced extra measures to help improve ventilation over the summer break. But anyway, we now need to make it work.

Rightly, special schools and alternative provision have been prioritised to receive their full allocation first, given their higher-than-average numbers of vulnerable pupils. When all schools can expect their full allocations is as yet another unknown.

The guidance from the Department for Education on how CO2 monitors should be used was sent out to headteachers in early September (DfE, 2021a; SecEd, 2021).

But rather than reflecting existing advice from the likes of SAGE and the Health and Safety Executive, the DfE’s guidance, confusingly, seems to set out different threshold levels of when action should be taken to improve ventilation.

Both SAGE (2021) and the HSE (2021) say that concentrations of CO2 should be kept at below 800 parts per million (ppm) in areas where there is continuous talking.

The DfE guidance, on the other hand, states that a consistent value of over 800ppm should be seen only as an early indicator to increase ventilation. It states that action only needs to be taken when readings are consistently higher than 1,500ppm.

In the absence of any explanation for this discrepancy, allowing nearly double the concentration advised by the expert bodies is rather disconcerting. We have asked the DfE to explain this contradiction.

The SAGE guidance also states that in rooms where loud speech is happening, additional mitigations such as face coverings and restricting the size of groups should be implemented.

In May, UNISON argued that the government was wrong to remove the recommendation for secondary schools and colleges to get rid of all measures such as face coverings. However schools can use their flexibilities within the operational guidance (DfE, 2021b) to reintroduce mitigations now, as infections continue to stay high.

A further concern is that the DfE’s CO2 monitoring guidance states that there is no need to stop using a room in order to improve ventilation, no matter how high the CO2 reading is. Doesn’t this bring in to question the point of the monitors?

In New York City, any room that does not meet stringent safety standards is not used for instructional purposes until it is put right. Air filters are being installed in every classroom and their commitment to protecting staff, students and families is clear. The contrast to our government’s approach is stark.

Finally, the DfE’s CO2 monitoring guidance gives little advice on how to go about actually improving ventilation other than mentioning opening windows and providing a few links to other organisations’ websites.

There is much more that can be done. In our joint union guidance we share good practice (UNISON, 2021). This looks at whether mechanical or natural ventilation can be used, advises on ensuring air bricks aren’t obstructed, setting air handling units to maximise outdoor air over recirculated air, starting ventilation ahead of the working day, and fixing windows that cannot be safely opened, to give just a few examples.

Perhaps most significantly the government admitted in an answer to a Parliamentary question that they have “not provided specific additional funding for schools to improve classroom ventilation since January 2021” (UK Parliament, 2021).

The benefits of ventilation in the control of all airborne diseases (not just Covid) are well understood and accepted, and we already know that air purifiers work. Good ventilation also aids student concentration, so will continue to pay dividends in relation to learning even when the pandemic is over.

While the £25m investment in CO2 monitors is a start, it will only be a sound investment if schools are equipped with the best possible guidance and additional funding to take action to improve ventilation.

As we the autumn begins to take hold and temperatures drop the chance to avoid freezing school staff by finding other ways to improve ventilation could be a quick win for the new ministerial team. Let’s hope we will not need our coats indoors again this winter.

Further information & resources

  • DfE: Access to the DfE’s guidance for using CO2 monitors – How to use CO2 monitors in education and childcare settings – as well as delivery forecasts per-school for the coming weeks (September 2021a):
  • DfE: Guidance: Schools Covid-19 operational guidance, last updated August 2021b:
  • HSE: Ventilation and air conditioning during the coronavirus (COVID-19) pandemic, accessed September 2021:
  • SecEd: Covid: Classrooms should still be used, DfE says, even if CO2 readings pass 1500ppm, September 2021:
  • SAGE: Role of Ventilation in Controlling SARS-CoV-2 Transmission, accessed September 2021:
  • UK Parliament: Written questions, answers and statements: Schools: Ventilation, July 2021:
  • UNISON: Joint union guide to improving ventilation in schools and colleges, NEU, GMB, UNISON, Unite, September 2021:


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