Ventilation and Covid-19

The HSE states that appropriate standards of ventilation in indoor environments will help prevent (but not eliminate) the spread of COVID-19.  Coronavirus particles are spread through the air as droplets or aerosols, which can stay in the air in enclosed rooms for several hours.  Good ventilation helps dilute the amount of virus in the air by dispersing any particles and reducing the potential for concentration of virus in the air.

Ventilation is the process of bringing in fresh air from outside and removing indoor air, which may be stale, contain pollutants or impurities or be hot and humid, due to activities taking pace in the area.

By taking measures to increase the volume of outside air entering a building, along with the other baseline protective measures which are in place such as cleaning and personal hygiene, the risk of spreading COVID-19 can be reduced. 

Improving air quality and ventilation in our facilities

The University has a duty to make sure there is adequate ventilation in enclosed areas of the workplace.

The institution continues to follow the latest Scottish Government and HSE advice/guidelines to ensure that our facilities are sufficiently ventilated - this document outlines what measures are in place and provides a bit more information about how they work in practice.

Ventilation at the University

What kind of ventilation do we have at the University?

The method of ventilation across campus varies and depends on the building, age of building, and use of building.  As a result, many of our buildings have a mixture of natural and mechanical ventilation, with either (or both) systems in different spaces.

Natural ventilation relies on doors, windows and other openings such as trickle vents, air bricks or grilles to provide fresh air, and this remains the primary effective method of increasing natural ventilation.  Wherever it is practical, safe and secure to do so, this approach should be adopted.

Mechanical ventilation uses fans to move air into and out of rooms. Ventilation design may be specific to the setting, so assessing the requirements and performance of ventilation systems in needs engineering expertise.  In small spaces and buildings there may be ventilation in the room, but larger buildings are likely to use a network of ducts and fans to blow clean air into rooms and/or extract the stale air.

What are we doing to maximise air quality?

Assessing the requirement and performance of ventilation systems in many environments requires engineering expertise. 

As a result, Campus Planning Group (CPG) asked Estates and Facilities to undertake surveys of the ventilation provided in our centrally timetabled teaching spaces across campus, with a focus on ensuring that ventilation and room capacities in these centrally timetabled spaces were prioritised so they could be timetabled at pre-Covid capacities from September 2022.

This involved

  • ascertaining that mechanically ventilated spaces were functioning at optimum levels
  • looking at ways of improving our ventilation - where possible
  • looking at potential additional interventions and mitigations to (where possible) improve air quality 

Estates and Facilities referenced building regulations, HSE, CIBSE and current Scottish Government guidance as part of the review and received support to complete the surveys from external contractors.

What did the mechanical ventilation surveys involve?

The surveys involved physical inspection of the areas/spaces by accredited external contractors engaged through Estates and Facilities.  The contractors checked:

  • the amount of air supplied to the room
  • the type of ventilation in place, for example is the space mechanically or naturally ventilated
  • ventilation systems are set to fresh air to maximise their effect

CIBSE (Chartered Institution of Building Services Engineers) guidance makes reference to provision of adequate air change in rooms and spaces and again this has formed part of the approach in assessing these areas.

Have all ventilation assessments been completed?

This work has been completed and some areas have been identified for improvements - work on this is ongoing through August and early September.

The assessment identifies the ventilation capacities of the space at different outputs, which informs whether further mitigations / interventions are required, such as opening windows or doors to create natural ventilation.

Please be reassured that we have assessed spaces through our own experienced teams and external specialist teams and that we will continue to monitor these spaces. 

What measures have been put in place to improve ventilation in mechanically ventilated spaces?
  • air-handing units have been adjusted to allow these to operate on full fresh air with no recirculation
  • all planned maintenance of ventilation, heating and cooling systems continues to carried out as required to ensure our systems are checked and working properly
  • all ventilation systems within the University were designed to comply with building regulations at time of construction.  The existing ventilation rates in all of our mechanically ventilated rooms meet CIBSE guidelines and statutory requirements.
Can Covid-19 be transmitted through ventilation systems?

There is no evidence to date that the virus is transmitted through a heating, ventilation, and air conditioning system to result in disease transmission.  Rather, a good ventilation system will help to remove air that may otherwise contain virus particles.

Do revised occupancy levels in rooms still apply?

Room capacity restrictions have been removed from all mechanically ventilated spaces and naturally ventilated teaching spaces, where air purification units have been installed.

The capacity of other naturally ventilated spaces may be increased (i.e. above the “1m spacing” occupation figure) where CO2 confirms ventilation is adequate.

Air Filtration Units (sometimes referred to as air purifiers or cleansing units)

Do air filtration devices improve ventilation?

Air filtration units essentially work by cleaning the air, which may include pollutants, allergens, and toxins.  They may be suitable for spaces where there is insufficient ventilation and the ventilation can’t be improved.  

There is currently very little evidence that air filtration units are an effective control to prevent COVID-19, however the principles of air cleaning suggest that they may be useful.  Air filtration devices are therefore likely to be effective but are not a substitute for good ventilation.

CPG has asked Estates and Facilities to purchase and install air filtration units with HEPA filters for naturally ventilated, centrally timetabled teaching spaces to support teaching activities returning to pre-Covid capacities for AY22/23.

How do these devices work?

Contaminated air is drawn in at the base of the air filtration unit and is blown out clean at the top. Since the air is cleaned several times every hour (rather than just once) a continuous flow of clean air is guaranteed whilst the unit is turned on.

The air cleaning units come in different sizes, calculated based on the size of the room.

The air filtration units are pre-set to ensure six air changes per hour in line with guidelines, and to ensure they operate at a low noise level - please:

  • do not attempt to change the settings on the units
  • do not cover the units
  • do not switch the unit off - either on the unit itself or at the wall.   

The units will be monitored and maintained through Estates and Facilities.

Queries and questions about air cleansing units, or any issues regarding their operation should be directed to

Which rooms have been provided with air purifiers?

A list of rooms that have been provided with air purifiers can be downloaded here

Note that those rooms in red currently have an air purifier while works to mechanical ventilation are completed. 

The Role of CO2 Monitoring

How are we assessing whether rooms have good to reasonable levels of ventilation?

Carbon dioxide monitors can identify where ventilation is poor in spaces.  CPG asked E&F to undertake CO2 monitoring in centrally timetabled teaching spaces, and to offer it in other areas when requested and where concerns have been raised about the quality of ventilation.  Estates and Facilities have therefore been undertaking CO2 monitoring in a variety of spaces across campus through AY21/22. 

The monitors have been helpful in providing an indication on the current air quality within a room and the efficiency of the room’s ventilation when it is in use - but they do not directly measure the likelihood of Covid transmission.   

What does CO2 monitoring involve, and what does it mean?

CO2 is measured in parts per million (ppm).  A value of 800ppm or below indicates well-ventilated space, but not one that is Covid-19 risk free. 

Sustained and prolonged values above 1,500ppm are likely to indicate poor ventilation, therefore the CO2 monitors are set to produce an audible alarm at 1,500ppm in real time.

Does the presence of a CO2 monitor in a room mean the space is safe to use?

We are undertaking ad hoc monitoring of some rooms into the first semester in AY22/23.  Rooms which are being monitored are centrally timetabled, mechanically ventilated rooms where it is not possible to increase the level of mechanical ventilation. 

Therefore, as part of our assessments you will see mobile monitors in some areas, but not all.  Not every room will need or require a CO2 monitor.

The CO2 sampling approach is in place to provide ongoing reassurance that spaces are being checked and are safe to use.  

How do I ask for a room to be monitored for CO2?

The following rooms do not need to be monitored for CO2 because other mitigations are in place to manage air quality:

  • Centrally timetabled teaching rooms which have air purifiers
  • Most centrally timetabled rooms which are mechanically ventilated (see above)
  • Rooms which are occupied by small numbers of people but have good natural ventilation

If you have a concern about a room or a lab you can request that it be monitored on an ad-hoc basis.  Please email giving the location and room number of the room and the reason for the request for monitoring. 

Is there a link between CO2 levels and transmission of COVID?

No, there is no direct link.  A high level of CO2 suggests that there is not enough fresh air in the room - it does not indicate the presence of Covid-19, just that the virus may build up in that room if someone who is infectious remains in it.

Please remember, building users also have a responsibility to take relevant appropriate action when the rooms are being used to ensure that rooms are appropriately ventilated (e.g. opening doors and windows to maximise air flow and air change).

Do we have any spaces where the CO2 levels are automatically checked?

We have some spaces where we can check the effectiveness of the ventilation systems and monitor CO2 levels automatically through inbuilt sensors in the building management system.  A high CO2 level detected results in an automatic adjustment of fresh air into the space.

Why is CO2 monitoring not taking place in every room?

Our approach to this is risk based, applying the principles of “As Far As Reasonably Practicable” through Health & Safety at Work Act and Statutory Regulations. This means the focus is to randomly sample areas of concern whilst ensuring that all other spaces are adequate and appropriate for use.

What about the ventilation levels in corridors and circulation spaces, and changes in levels throughout buildings?

People who are moving throughout a building tend to be short duration transient movements, and therefore the level of ventilation has less significance in relation to the risk.

How do we check levels of CO2?

Outside air has a level of around 400ppm CO2.  Our monitors are calibrated for readings between 800ppm and 1500ppm. 

Where rooms repeatedly show readings of more than 800ppm attempts should be made to improve ventilation. The following can be considered:

  • windows opened
  • doors opened (unless they are fire doors that cannot be left open)
  • occupancy levels not exceeded

If the readings consistently remain close to 1,500 ppm, a reassessment of capacity will be undertaken.

If readings are above 1,500ppm, this indicates a poor level of ventilation.  The audible alarm on the monitor will sound, indicating that the space should be vacated until the level of CO2 drops below 1,000 ppm.

Please do not move the monitor from where it has been placed in the room, nor attempt to deactivate the audible alarm or tamper with the monitor in any way.  The alarm will cease when the ventilation levels improve.



Can I see the results of the CO2 monitoring?

The results from the CO2 monitoring process are published on the University CO2 Monitoring Sharepoint site, available here: 

All staff are able to access this information and are able to “follow” the site (by clicking on the star at the top right hand side of the web page).  This provides alerts to your inbox when the site is updated.

Estates and Facilities download and analyse the data to establish any trends, and with support from the Health, and Safety team, advise on and take action where needed. 

Research has indicated that the risk of airborne transmission of Coronavirus depends upon the number and spacing of people in an enclosed space, what they are doing, and how long they are within the space for as well as how well the space is ventilated.  The effectiveness of ventilation in many environments is therefore strongly influenced by user behaviour and activities.

Fortunately, the data yielded from the CO2 monitoring over the past year indicates that only a few spaces at the University which were monitored had readings over 1,500ppm for more than a few minutes.

Where can I do some further reading on ventilation?

Further information on ventilation is available on the Scottish Government website, at

Improving Ventilation

How can ventilation be improved in non-mechanically ventilated spaces?

A good supply of fresh, clean air reduces the risk of coronavirus transmission.

In naturally ventilated spaces, ventilation can be improved by partially or fully opening windows, air vents and doors that don’t need to remain closed for other purposes (for example, fire doors).  This allows a flow of air through the room.  Windows do not need to be open all the time to improve ventilation - bringing fresh air into a room by opening a door or a window even for a few minutes at a time helps remove older stale air that could contain virus particles and reduces the chance of spreading infections.

Fire Exit doors (i.e. which open to the outside) may be opened provided they are closed immediately at the end of the class.

Opening windows in colder weather is not always possible - shouldn’t windows remain closed at this time for comfort?

In line with guidance from CIBSE (Chartered Institution of Building Services Engineers) reasonable thermal comfort should be the target for all users of rooms.   That said, if natural ventilation openings are the only mechanism for delivering fresh outside air it is important to not close these completely - it is better and advisable to open all the windows or vents even just a small amount to aid air flow. 

It is therefore strongly recommended that windows in naturally ventilated spaces are opened to aid air throughput, although this is not required where air purifiers are in place.

The weather can affect the amount of air that flows through openings.  In cold or windy weather a smaller opening can be as effective at bringing fresh air in as a larger opening when the weather is calm and warm.

If windows have openings at both the top and the bottom (such as sash windows), using just the top opening in the colder months will help incoming fresh air warm up as it mixes with room air, reducing draughts.  In warmer weather, use both the top and bottom openings as this will help provide even more airflow.

What should I do if I cannot open my windows to naturally ventilate my area?

All windows around campus have been checked to ensure that they can be opened. However, if for some reason you do find that somewhere in your area some windows have seized shut or are sticky to open, please contact the Estates and Facilities Helpdesk via so that these can be attended to.

Who do I contact if I have concerns regarding ventilation in my space in general?

If you have any specific concerns (faults or specific issues regarding ventilation), please contact the Estates and Facilities helpdesk via for further advice and guidance.