Last reviewed 12 April 2021

As pupils and staff return to more normal classroom routines, health and safety must keep in step. To date, schools are reported to be doing well. But vigilance will have to continue in the summer term. Jon Herbert reports on initiatives to improve natural and mechanical ventilation.

If, as planned and hoped, schools and educational settings are able to return progressively to more familiar ways of working as summer approaches and throughout the year, they will have a long list of priorities.

One of the highest will be not only to have in place, but also to continuously and rigorously enforce and maintain, stringent physical safety measures – one of the most important is efficient ventilation.

As schools reopened for the spring term, detail monitoring by the HSE, supported by spot checks and inspections, found a generally very high level of compliance and responsible innovation designed to minimise person-to-person contacts.

However, one of the key factors in reducing airborne transmissions of the Covid-19 virus is good natural and mechanical ventilation of school workspaces, or a combination of both.

With this in mind, HSE issued in March 2021 detailed guidance notes – Ventilation and air conditioning during the coronavirus (Covid-19) pandemic.


A brief review of what HSE’s phone calls, spot checks and inspections found late in 2020 may be helpful (Health and safety spot checks and inspections during coronavirus (COVID-19)).

HSE, in fact, contacted some 5,000 primary and secondary school in England and Wales to check whether they were following relevant government guidelines effectively. These included a proportional number of state-maintained, independent and special schools.

Initial calls showed that circa 80% had a good understanding of guidance and what being Covid-19 secure involves. Of the remaining 20%, HSE carried out more than 1,000 follow-up site inspections. As a result, no further action was needed for more than 50%; for most of the other 50% verbal advice was given on minor issues.

Less than 1% of inspections identified health and safety failings that required formal interventions and improvements.

Lessons learned

Some common issues were spotted and addressed in a small number of schools. These included: the need for stricter social distancing in staff rooms and kitchen/canteens; more rigorous cleaning schedules; and better ventilation inside school buildings.

As explained in more detail in a moment, ventilation in most schools currently relies on windows and doors being kept open for long periods. A problem for staff and students is being able to maintain an acceptable and workable balance between room temperature and adequate air flows.

With warmer weather ahead, this problem is likely to recede. However, with the strong possibility of precautions still being needed in the lead up to next winter, the issue could remain important.

Other important points the inspections identified included: - fire doors being propped open wrongly to encourage more ventilation; inappropriate rooms being used for isolating suspected infection cases; and poor arrangements for managing visitors and contractors.

Innovative initiatives

On the positive side, inspections also noted many innovative ways in which some schools are promoting good practice that others may wish to copy.

  • Pupils being issued with coloured lanyards to identify their bubbles.

  • Brightly-coloured ground markings in playgrounds to encourage distancing between parents and pupils at drop-off and collection times.

  • Video walkthroughs of Covid-secure arrangements.

  • Classroom seating plan to help with self-isolation.

  • Click-and-collect apps for buying food in canteens.

  • Video conferencing for staff meetings.

  • Phone use in classrooms between staff members.

Ventilation and air conditioning advice

The law stipulates that employers must ensure adequate fresh air (ventilation) in enclosed workplace areas – both generally and in schools – and this has not changed during the pandemic.

Providing fresh air can be by natural ventilation with passive air flows through windows, doors and vents that are totally or partially open at all times.

Alternatively, good air flows can be as a result of mechanical ventilation with fans and ducts that bring outside air indoors, or through a combination of natural and mechanical systems.

Ventilation is so important that it should rank alongside social distancing, keeping workplaces clean and frequent hand-washing.

The guidelines aim to help in several places.

  • Assessing the risks of aerosol virus transmission in enclosed spaces.

  • Identifying poorly ventilated areas.

  • Identifying steps to improve ventilation.

Why ventilation is important

Ventilation reduces the amount of airborne virus and helps to decrease aerosol transmissions – small particles in the air emitted by an infected person/persons.

It is also important to note that good ventilation cuts aerosol risks but not direct droplets or contact transmission between close people.

Simple safety steps

The first safety steps are to:

  • ensure infected people do not enter workplace or classroom areas

  • provide adequate ventilation

  • limit the number of people in any particular area

  • avoid activities that increase deep breathing – singing, exercise, shouting

  • ensure people spend less time in occupied areas.

Identifying poorly ventilated areas

This step precedes risk assessment and involves:

  • looking for workplaces with no natural or mechanical ventilation

  • checking the operation of mechanical systems

  • providing outdoor air, temperature controls, or both – recirculated air is poor ventilation!

  • remembering that stuffy or smelly air is bad.

Assessment of fresh air (ventilation)

Several factors are involved here. They can include a review of ventilation processes – natural or mechanical. This is in the context of different areas often relying on different ventilation set-ups.

Floor or design plans can be helpful here. Walking the floor and taking notes in an alternative. Changing rooms, break-out areas and canteen facilities are examples. Not being able to tell if ventilation is adequate is often a sign of poor ventilation.

The number of people using a particular area

The greater the number of people, the higher the risk. Reducing numbers reduces risk.

Other factors include length of occupancy. The longer the time people spend in an area, and the higher the turnover of people using it, the greater the risk.

Area size

In general, the larger the area the lower the risk. The reasons for this is that large buildings and rooms are usually designed with higher ventilation rate which dilute the virus.


As already mentioned, deep breathing increases aerosol generation and transmission risks, even with good ventilation. Therefore, moving strenuous activities outside is a wiser option.

Desk and ceiling fans

These are not a good idea. Air may feel fresher but risks are simply being transferred and spread. However, buildings with local extraction ventilation (LEV) systems are useful providing they move air within a building to the outside.

Complex ventilation systems

Old buildings, and buildings with multiple floors and rooms, may rely on different systems in different places. Guidance for complex ventilation systems is available from the Chartered Institution of Building Service Engineers (CIBSE) ( The expert advice of a ventilation engineer may be needed.

Talking to staff members

Staff should be aware of the findings of any risk assessments so that they know how they can subsequently help in: reducing infection risks; and noticing failures, non-compliance and infringements.

Explaining the reasons for enhanced ventilation with staff and pupils is strong recommended as it usually increases what they find acceptable from a personal comfort point of view.

Other steps to improve a temperature/ventilation balance may include: opening high level windows: and relaxing dress codes so that extra layers of warm clothing can be worn.

Improving natural ventilation

This can be a tricky one to monitor on cold blustery days and will probably depend on how far windows, doors and vents are left open, excluding fire doors of course!

Buildings are designed to provide adequate ventilation; if this is not possible for any reason then occupation can be suspended until improvements are made. Windows and doors should not be closed completely.

Winter low temperatures and winds will increase natural ventilation through gaps and openings that do not have to be opened as wide as in warmer calmer weather. More advice is available at

Purging or airing rooms

Airing rooms frequently improves ventilation. Opening doors and windows fully – preferably when a room is not occupied – is a good idea.

Improving mechanical ventilations – including air conditioning

Making sure that mechanical ventilation systems do bring fresh air into buildings often means speaking to the people who manage them to ensure that flow levels are adequate, and units are maintained in line with manufacturers’ instructions.

Lowering mechanical ventilation rates just because the number of people in a room happens to be reduced temporarily is not good practice. Rather, base ventilation rates should be calculated on the maximum normal number of people using a specific area. Extending ventilation operational times before and after people occupy any particular room or space is also recommended.

As already mentioned, recirculation units, including air conditioning systems, do actively pose risks. Systems should, therefore, be set on maximum fresh air and minimum recirculation. Fan convection heaters should only be used in well-ventilated areas.

Air cleaning and filtration units

These can be used to reduce airborne transmission where maintaining adequate ventilation is otherwise not possible.

But they are not substitutes for ventilation. The most suitable types are high-efficiency filters and ultraviolet-based units. The size must be appropriate for the area in which they are to be used.

Ventilations in vehicles

A few simple rules are useful here. Vehicle systems should be switched on whenever vehicles are in use; they should be set to draw in fresh air and not on recirculation.

Windows should preferably be kept open at all times; leaving the heater on can make this more comfortable. Whenever safe and possible, doors should be left open between use by different groups of passengers to change air quickly.

Department for Transport guidance on preparing vehicles is available online. HSE guidance is also available on social distancing in vehicles.


  • Checks on some 5,000 schools carried out by the HSE in recent months have shown that in the majority of cases (80%) staff do understand clearly what is needed in ensuring Covid-19 security.

  • Most schools put these principles into practice. Many have also been innovative, with creative ideas that others may want to follow to control present and future pandemic health and safety risks.

  • However, there will be a continuous need to update and enforce health and safety efficiency and security measures throughout the summer term and current year, hopefully as restrictions are reduced.

  • Ventilation is important. Reducing airborne transmissions of the Covid-19 virus very much depends on good natural and mechanical ventilation of school workspaces, or a combination of the two.

  • HSE issued detailed guidance notes Ventilation and air conditioning during the coronavirus (Covid-19) pandemic in March 2021.

  • The guidance shows why ventilation is important; simple steps that can be taken; how to identify poorly ventilated areas; assessing fresh air flows; the importance of room size; how activities can increase risk; why desk and ceiling fans should not be used; how to manage complex ventilation systems; why talking to staff members is important; improving natural ventilation, purging and airing rooms; improving mechanical ventilation – including air conditioning systems; air cleaning and filtration units; plus ventilation in vehicles.