Most schools should by now have received their allocation of CO2 monitors from the DfE.

Ideally there should be one monitor for every classroom, but most schools will need to top up their DfE allocation to ensure regular, systematic monitoring across all classrooms.

School environment
How to use CO2 monitors

Step by step guide to placing, using and understanding CO2 monitors in your classroom.

A more technical poster is also available to download

Why should we use CO2 monitors?

The law requires employers to ensure an adequate supply of fresh air in the workplace and this has not changed during the pandemic. 

Good ventilation, together with social distancing, mask-wearing, frequent handwashing, minimal mixing and isolation of positive contacts, can help reduce the risk of spreading coronavirus.

Where people occupy a workspace, they will naturally exhale vapour droplets and airborne aerosols; these may contain small particles of the COVID-19 virus.  If a workspace is well ventilated, these particles are more likely to be dispersed, reduced or removed from the air.

The level of carbon dioxide (CO2) acts as a proxy for the Covid-19 risk as people exhale airborne viruses when they exhale CO2. To check the situation in your workplace, use carbon dioxide monitors to check whether ventilation is sufficient to keep CO2 levels below 800 ppm.

Indoor air at 600 to 800 ppm carbon dioxide indicates a relatively well-ventilated room.

Carbon dioxide monitors are not a solution to the problem of poor ventilation. They will indicate a problem that must be solved.

This guide should be used in conjunction with the joint union guidance on ventilation for comprehensive guidance on measures to take to improve ventilation in your school and classroom.

The NEU’s advice, as far as CO2 thresholds are concerned, is that if your monitor reading exceeds 800ppm your employer must act!  Read our advice on appropriate action.

Where to place CO2 monitors

  • Ideally one per classroom, placed at head height when seated
  • Not positioned next to ventilation outlets such windows or doors or vents as this could distort readings
  • At least half a metre away from occupants
  • CO2 readings build up as soon as people enter a room, but if there’s good ventilation it will level off
  • Check the monitor works by taking it outside. Outdoors the reading should not exceed 400 – 420ppm.
  • Take readings over a whole day or a couple of days of consistent use so it can be seen what makes levels go up and down.  Check readings mid-way through a lesson and at the end.
  • Schools can use this BOHS guide to help prioritise which classrooms need monitoring most Ventilation Tool – Breathe Freely

Recording your CO2 readings

Your employer should be monitoring readings from all the CO2 monitors in your school.  If this isn’t happening, request that this is addressed but, in the meantime, use a monitoring sheet like the one below to record the readings you take from the CO2 monitor in your classroom. Where this happens, all staff should pass their readings to management who should be asked for regular feedback on the findings.  If your school has a safety rep it is a good idea for them to be involved in the monitoring of C02 levels in the school. They should be given facilities time to fulfil this role.

Air quality monitoring

CO2 Air quality monitoring sheet

Include in comments: numbers of people in classroom and any other useful information that may affect the readings.

Tips to improve ventilation in the workplace

  • Open doors and windows
  • Switch off the air-recirculation function on air-conditioning
  • If fitted, air handling units should be set to draw in the maximum fresh air
  • Ensure curtains and equipment are not blocking any windows or air vents
  • Reduce numbers in the room/ Use larger room/ Work outdoors/Reduce time spent in certain rooms

In cold weather

  • Relax the dress code to allow staff and students to wear warmer clothes
  • Provide oil filled radiators

For more detailed guidance on improving ventilation, see the joint union guidance on ventilation.