Ventilation and Covid-19

One of the key routes of possible infection with Covid-19 is through the inhalation of the virus through the air.

The Health and Safety Executive (HSE) has published extensive guidance on Ventilation and air conditioning during the coronavirus (COVID-19) pandemic.

Adequate ventilation reduces how much virus is in the air. It helps reduce the risk from aerosol transmission, when someone breathes in small particles (aerosols) in the air after a person with the virus has been in the same enclosed area.

The risk is greater in areas that are poorly ventilated. However, whilst ventilation reduces the aerosol risk, it has minimal impact on droplet transmission, where people are within two metres of each other, and contact transmission, touching surfaces.

Identifying poorly ventilated areas is very important and can be done using carbon dioxide (CO2) monitors, which is recommended by the HSE. The HSE has produced detailed guidance on the use of CO2 monitors.

In any room, CO2 levels should be below 1000 parts per million (ppm) and ideally lower than 800ppm.

High CO2 levels are not just hazardous in terms of Covid-19, they also impact on the ability of pupils to learn. Therefore, ensuring adequate ventilation is an educational issue just as much as it is a health and safety issue.

The Government has announced that all settings will be provided with CO2 monitors during the autumn term, with one monitor being provided for every two spaces within schools. Special schools and alternative provision settings will be prioritised for delivery in September, with mainstream settings receiving the monitors during the term, although it is unclear when this will be.

Schools must not wait for the delivery of CO2 monitors to take action to improve ventilation and delays in delivery cannot be used as an excuse for inaction. Rooms without sufficient natural/mechanical ventilation, where there is a feeling of ‘stuffiness’ or bad odours, or where there are any other concerns about ventilation will require measures to be taken irrespective of whether monitors are available or not.

Where there are concerns about ventilations, members and NASUWT Representatives should raise these with management in the first instance. If the response in insufficient, you should contact the NASUWT for further advice.

Placement of CO2 monitors

CO2 levels vary within an indoor space. The HSE recommends that CO2 monitors are placed at head height and away from windows, doors or air supply openings.

Monitors should also be positioned at least 50cm away from people as their exhaled breath contains CO2. If monitors are placed too close they may give a misleadingly high reading.

HSE video on ventilation

Cold weather

The HSE is clear that providing adequate ventilation does not mean people have to work in an uncomfortably chilly or cold workplace. Again the use of CO2 monitors will be useful to measure the levels of ventilation and prevent the need for windows and doors to be open unnecessarily.

In winter conditions, with higher outside wind speeds, windows and doors partially open can still provide acceptable ventilation while keeping the workplace comfortable. Air filtration units could also be utilised.

Heating systems should be turned up and turned on earlier in the morning so that the fabric of the building is warm. Fan convector heaters can also be used if the area is well ventilated or if they are equipped with HEPA filters.

Risk assessments

Health and Safety Regulations already state that all workplaces must be adequately ventilated and the HSE guidance emphasises this in terms of Covid-19 and the potential for airborne transmission in workplaces that are not well ventilated.

If they have not already done so, all employers should urgently undertake a risk assessment of all rooms, which should include the levels of ventilation in order to identify poorly ventilated rooms. This is especially important given the removal of most other mitigations from 19 July.

Any existing risk assessment must also be reviewed prior to changes in other mitigations.

Members should avoid working in rooms that are poorly ventilated. Poorly ventilated rooms will often have:

  • no mechanical ventilation and no or limited natural ventilation;

  • mechanical systems that do not provide outdoor air, i.e. only recirculate air;

  • a feeling of stuffiness or bad odours.

If members have concerns around the ventilation in their school, they should raise this with their line manager, drawing their attention to the HSE/CIBSE guidance and request that a CO2 detector is provided.

Guidance on the use of air conditioning systems is also available from the Chartered Institute of Building Services Engineers (CIBSE).

Use of air cleaning and filtration units

Air cleaning and filtration units which employ either high efficiency particulate air (HEPA) filters or ultraviolet-based devices can also help remove viruses and other pathogens and allergens from the air.

However, they are not a substitute for ventilation and the HSE has been clear that employers should prioritise any areas identified as poorly ventilated for improvement in other ways before considering using an air cleaning device.

The NASUWT would strongly recommend that they are used in addition to, not instead of, adequate ventilation. The Government has announced it is conducting a trial of filtration units in schools, but this is not expected to report until 2022.

If you are unhappy with the response from their school, you should contact the NASUWT for further advice.

Given the announcement on 6 July of the intention to remove the requirement for distancing and face coverings from Step 4, it is particularly important that all the guidance on ventilation is strictly adhered to.


The benefits of ensuring and using adequate ventilation are clear during the Covid-19 pandemic, but the benefits extend beyond Covid-19 and any investment will be effective post Covid. For example, decreasing CO2 levels will have a positive impact on the ability of pupils to learn.

Ventilation does not only remove Covid-19, but also many other viruses and pathogens. Increasing ventilation, combined with the use of air filters and enhanced cleaning routines, could reduce levels of general sickness absence, again improving educational outcomes and reducing costs.