Appendix 3

Advice on CO₂ monitors

Ventilation is an important factor in mitigating against the risk of aerosol transmission of coronavirus (see Chapter 6).

The Health and Safety Executive and the SAGE group of scientific advisors recommend the use of CO₂ detectors. These could warn when indoor areas are reaching unsafe COVID-19 transmission levels. They can be bought for as little as £35.

A CO₂ concentration of below 800 parts per million (ppm) should be aimed for. Values above 1500ppm indicate poor ventilation with a higher risk of aerosol transmission of the coronavirus. SAGE says 800ppm may not be sufficient for activities which have a potential for high aerosol generation, such as singing and aerobic exercise and these should be avoided indoors.

The NASUWT teaching union says mechanical systems in newer schools may already be fitted with CO₂ sensors which should be switched on. Although a CO₂ detector is not required in every room, the union strongly recommends, in line with HSE and SAGE advice, that all schools purchase some detectors.

It adds that ventilation may differ throughout a workplace, for example in different buildings and rooms, and risk assessments should acknowledge this. The virus is known to remain suspended in the air for longer in cooler environments, and workplaces with cooling systems must pay particular attention to ventilation.