Clean air works – let’s make it core to a healthy and productive learning environment.

by | Jun 21, 2022 | Blogs, Theme 2: Transmission modelling | 0 comments

Why attendance focus reiterates the need for good ventilation in schools

After three disrupted academic years, it is evident minimising school absences for all students is vital. In some areas attendance remains stubbornly low and there are significant regional variations.

Indeed, boosting attendance is a key focus area for the government at present – which given recent Department for Education (DfE) data that showed the negative impact on attainment that missing even a few days school can have at key stage 2 and key stage 4 is not surprising.

As such, whatever schools can do to reduce absence through illness – whether Covid-19 or other airborne illnesses such as colds or flu – should be utilised.

One big way this can be achieved is through ventilation. It’s an issue that garnered a lot of airtime over the pandemic but has, currently, dropped off the agenda slightly as we adjust to ‘learning to live’ with Covid-19.

However it would be remiss to ignore ventilation and its importance in schools – especially if we really are ‘learning to live’ with Covid or looking to boost attendance – because it, like those other respiratory infections, spreads through particles released in the air when we talk, cough, sing, sneeze and breathe – common activities in school classrooms where children and adults work in close proximity.

Good ventilation though, can minimise this risk of infection by ensuring that any particles of Covid-19 released into the air are diluted and blown away, lowering the chance of someone breathing in enough particles to become infected.

Ventilation also doesn’t just reduce the risk of illness. Studies have shown that it can also improve pupils’ concentration, cognitive performance, and productivity in addition to  reducing a range of respiratory symptoms. 

Schools with better ventilated classrooms have even been shown to have higher test scores.

Ventilation for good health is a simple idea in theory and key physical principles suggest that if you double the amount of fresh air in a room you halve the airborne risk of exposure.

In reality, it is hard to measure real-world impacts of ventilation and air cleaning on infection rates as there is limited data on both ventilation and numbers of infections in different locations.

Nevertheless the evidence available does show ventilation and air cleaning can contribute significantly to reducing absence rates in schools.

For example, a study carried out in the USA looked at reported data from 169 primary schools and kindergartens on infection rates and actions taken to reduce transmission.

Those schools which had made ventilation improvements (e.g. opening windows and doors more frequently or using fans) had 35% lower incidence of infection while those that had also added in air cleaning devices showed a 48% reduction.

Another study which looked at multiple ‘super-spreading’ outbreaks showed that the size of the outbreak was correlated with ventilation rate, with poorer ventilation leading to higher numbers of cases.

Data also exists for other diseases. Respiratory illness in an army barracks was 33% higher in rooms where windows were closed, while a flu outbreak in nursing accommodation was 50% lower in a building with a higher ventilation rate,

Perhaps most notably for schools, higher ventilation rates in classrooms in California has been associated with reduced illness absence.

So we should be assured, ventilation works and has many benefits. How then do we do it best?

How to ventilate well

Assess and communicate the ventilation strategy:

Ventilation design can be different in every classroom and so the first step is to assess how a room is ventilated.

This can be done with the support of the site manager or building manager but it is also important to communicate how rooms are ventilated to the people who use them so they understand what works and why – and how to improve it.

For example, a walk round with staff or simple information posters can help staff identify ventilation devices and where air might be entering and leaving the room.

Maintain and use mechanical systems effectively:

Some rooms may be mechanically ventilated where air is provided to the room through a system of ducts and fans. Alternatively a room may have extraction fans or low-energy heat recovery ventilation units.

Where a room has one of these systems it is important they are regularly maintained and assessed and it is crucial that occupants of those rooms know how the system works.

During periods of high illness prevalence (for example, high or increasing levels of absences) mechanical ventilation systems should operate with more fresh air than usual.

It is also important that school staff know how to spot any potential problems with mechanical ventilation devices, e.g. through spot checks with CO2 monitors, and can report them so they are fixed quickly.

Use the windows well:

Many classrooms are naturally ventilated and rely predominantly on opening windows, doors or other vents to provide good airflow.

It is important to first check windows and vents are well maintained and can be used easily and safely.

Of course, some windows don’t open well, are out of reach, or cannot be opened on cold or wet days which can hinder ventilation.

However, there are several tips that can help to maximise ventilation with windows under different weather conditions or window quality:

  • Windows don’t always need to be wide open. Smaller window gaps can give as good ventilation on cold days as a wide-open window on a warmer or still/calm day.
  • Opening more than one window, or a window and a door, can help create more of a through flow, especially if they are on different sides of the room.
  • When the outdoor conditions are calm and still, providing window or vent openings at different heights in a room can help to create an airflow.
  • When it is cold outdoors, opening high level windows only can help to minimise cold drafts.
  • When the weather, noise, or pollution makes it difficult to open windows all the time, opening them for short bursts during breaks between lessons can still provide ventilation.

Use CO2 monitors to help manage ventilation:

Carbon dioxide (CO2) monitors can be a useful guide to show whether classrooms have sufficient ventilation.  

CO2 monitors work by measuring, in parts per million, or ppm, the fraction of CO2 in the air compared to other substances such as oxygen and nitrogen. In outdoor air, the CO2 is typically 400-450ppm.

When the room is occupied, if the indoor monitor normally reads around 800ppm or less then ventilation is likely to be good. A reading regularly over 1500ppm is an indicator of poor ventilation, particularly in a classroom.

Schools could use CO2 monitors in two ways.

Firstly, site managers or building managers can use them as part of a ventilation assessment. This may help with identifying where maintenance is needed or additional measures are required.

Secondly, CO2 monitors can be used directly by the people/staff/pupils using a room to manage ventilation and know if they need to open a window or switch on an air cleaning unit.

Top tips on using CO2 monitors

  • Look for monitors that are based on technology called Non-Dispersive Infrared (NDIR) as these are the most reliable
  • Position a monitor where it is visible. It should ideally be at breathing height (on a table or wall), at least 1m away from people and away from doors, windows or vents that may result in false readings
  • Most monitors work best when they are plugged in rather than using batteries
  • Many monitors self-calibrate and some take a few days to settle down. If you are regularly getting very low values when the room is occupied (less than 500ppm) or unexpectedly very high values, then check the monitor is working and manually recalibrate by measuring outdoors for around 15 min (should be under 500ppm) – and then using readings as you arrive in your classroom to guide you.
  • Avoid using a monitor in rooms with other CO2 sources such as gas hobs or Bunsen burners as you will get a false reading
  • When sharing  monitors between more than one room it is better to move them every couple of weeks rather than measuring for a short period of time
  • It is a good idea to experiment with a sensor to see how it changes with different windows open and different weather. Using a monitor regularly can allow you to learn which actions result in better ventilation.

The role for air cleaners

For classrooms with design issues or barriers to using ventilation devices that cannot be easily resolved, air cleaners, based on HEPA filters or ultraviolet disinfection (UV-C) can be a good, robust short-term solution that can be introduced to continually clean the air in a classroom.

There is growing evidence that air cleaners work well and they have been shown to remove virus particles from the air

Air cleaners do not provide ventilation so should always be used alongside some means of providing fresh air such as periodically opening windows.

There are a number of factors that need to be considered including noise, cost and maintenance but portable air cleaners are usually a straightforward intervention that can be implemented quickly and easily.

We previously wrote a guide on how to best implement HEPA filter-based cleaners.

Planning for the longer-term

We know ventilation and air cleaning work to reduce infection but for it to be effective we need to maintain this focus on school air quality for the long term.

It is no good reducing ventilation if there appears to be rates of infection or waiting until there is an outbreak before opening a window. Good ventilation in schools should be used as a background measure to prevent transmission from happening in the first place and to enable wider health benefits.

Furthermore, using air cleaning with filters can also bring major benefits in reducing exposure to outdoor pollutants from traffic, wood smoke, and industry. Air cleaning with filters can also reduce the pollen exposure that causes allergies and hayfever in the summer months.

All of this could help cut pupil and staff absence, boost attainment, and create more energy-efficient school sites too.

As such, now is the time to make the case for investing in better solutions for our schools – this may be new mechanical ventilation with heat recovery, more effective natural ventilation solutions, or longer-term implementation of robust air cleaning technology.

It may feel like a major step to plan new ventilation, and it may feel like an expensive step when budgets are already stretched; but the paybacks are likely to be huge and long lived.

The cost of implementing improved ventilation would save both the direct costs associated with enforced lockdowns, heightened pressure on the NHS, school closures, staff absence and the long-term indirect societal cost in lost education and opportunities.  

There are no magic bullets for eliminating airborne infections but everything points to ventilation and air cleaning as one of the best tools in the box to minimise impacts and protect children and staff.

Professor Cath Noakes, University of Leeds, Dr Henry Burridge, Imperial College


The authors would like to thank Prof Mark Mon-Williams, Dr Chris Brown and colleagues and participating schools in several studies including the PROTECT Covid-19 National Core Study on Transmission and the Environment led by HSE, the Class-ACT study funded by DHSC, and the SAMHE study funded by the DfE andEPSRC.

This blog is reproduced from a TES article: 


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