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Information reviewed and updated August 2022

SARS-CoV-2 is mainly spread via respiratory droplets including aerosols from an infected person who sneezes, coughs, speaks, sings or breathes in close proximity to other people. Droplets including aerosols can be inhaled or deposited in the nose and mouth or on the eyes.

Exhaled viral material can also settle on surfaces which a person may touch and then touch their eyes, nose or mouth, thus infecting themselves. 

Consequently good hand hygiene, regular surface cleaning and good ventilation and the use of face coverings in some circumstances are key Covid 19 risk control measures.

There are two main reasons why ventilation is important in helping to prevent the spread of Covid 19:

  1. The air movement or air turbulence created by ventilation causes exhaled droplets to fall from the air more quickly thus helping to reduce the risk that they will be inhaled by persons
  2. Ventilation and the associated provision of fresh air into a space and the resultant air exchange also helps remove smaller aerosols which may be hanging in the air 

There are two types of ventilation within UCD, mechanical and natural (some spaces operate a combined model of both mechanical and natural ventilation).

  • Mechanical Ventilation*

Mechanical ventilation introduces air into a space via the use of an air handling system. In general larger teaching spaces, labs, workshops, toilets and lecture theatres are mechanically ventilated, with supply and / or extract grilles fitted to the ceiling or walls.

In the main in UCD mechanical systems operate on a full fresh air supply, with no recirculation of used air between breathing zones in different work spaces, i.e. fresh air is pumped from outside the building into a space, and is then extracted and vented without being recirculated to the breathing zone of another space. In some areas there may be contained recirculation of air within the space for heating or cooling purposes. Some older supply systems which recirculated a small proportion of extract / used air have been modified and adjusted to now supply full fresh air only.

Whilst there is variation as to how different systems work depending on their age and set up, it is important to note that ‘used air’ is not actively recirculated between the breathing zones of different working areas within UCD buildings.

* A very small number of spaces in UCD are fitted with locally controlled recirculating air conditioning systems. These can be recognised visually as large units mounted on ceilings or walls. These units generally work in conjunction with supply of fresh air and local recirculation to warm or cool this air for comfort purposes. As long as there is a supply of fresh air these systems can be used but in the absence of a fresh air supply they should not be operated. Further advice can be obtained from Estate Services.

  • Natural Ventilation

Natural ventilation is the introduction of fresh air into a space via an open window (and in some cases an open door). Within UCD this type of ventilation is generally found in smaller teaching spaces, offices, etc.

All shared teaching and shared workspaces in UCD will continue to be reviewed and assessed by Estates Services as to the type and extent of ventilation present.

Mechanical Ventilation

All mechanical ventilation systems have been serviced and where necessary bearings, fans, filters, etc. have been replaced.

All mechanically ventilated teaching spaces have been assessed for their capacity to provide adequate ventilation in line with REHVA Covid 19 guidance. Systems have been set to run at a higher rate (i.e. introduce more fresh air than usual) for longer periods than would normally be the case, both starting earlier in the day and running for longer periods in the evening where appropriate. Any systems with the potential for air recirculation between spaces have been set up to provide fresh air supply only (i.e. 100% of supply air is drawn from outside of the building).

Any rooms not in compliance with these guidelines have been modified to improve ventilation, have had their capacity reduced or have been removed from use as a classroom. Where the ventilation of spaces has been modified this has been revalidated within the space and where necessary external guidance and advice has been sought.

In some cases the use of HEPA filtered air treatment units may be used in lieu of ventilation in some teaching spaces if an adequate level of filtration can be achieved. 

It should be noted that as ventilation rates are increased it is likely that there may be additional noise in rooms.

Faculty will be informed if a teaching space is to be removed from use for maintenance or other reasons and alternative arrangements put in place.

Mechanical ventilation systems have been set up so as to provide an optimum supply of fresh air. This is achieved in one of two ways:

  • CO2 sensors within the system monitor CO2 levels in the space and optimise air flow in response to CO2 levels. As CO2 levels rise (indicating higher occupancy) the rate of air supply increases, with the aim to keep CO2 levels below 1,000 parts per million (ppm)
  • For those ventilation systems without inbuilt CO2 monitors the supply fans have been programmed to deliver a constant supply 8-10 litres per second of fresh air per person assuming a 100% occupancy rate in the space.

Mechanical ventilation systems are monitored via UCD’s Building Management System. This system allows Estates Services engineers to monitor the operation of ventilation systems to ensure that they are functioning properly.

Natural Ventilation

Natural ventilation depends on the use of windows. Estate Services are continuing to assess naturally ventilated teaching space and shared workspace to ensure that there are openable windows present in every such space and that such windows are working correctly to allow for adequate ventilation.  

The adequacy of natural ventilation has been assessed using the 2019 Building Regulations Technical Guidance Document Part F (Ventilation). This technical guidance sets out minimum requirements for naturally ventilated spaces in order to achieve adequate ventilation based on the relationship between window openings and floor space. 

It has been suggested that local CO2 monitoring can be used as a proxy for air quality and thus the provision of adequate ventilation. As humans exhale they produce large amounts of CO2; up to 4% of your exhaled breath is CO2. A build up of CO2 in a space can be indicative of poor ventilation and consequently the measurement of same can be used as a indicator of air quality. It should be noted that CO2 levels are in no way linked to Covid 19 levels in a space, the CO2 level is an indicator of the rate of ventilation / air exchange from a space.

In spaces that are mechanically ventilated Estates Services personnel can monitor the performance of the systems via the University’s Building Management System. This gives them real time access to information on air flow and system performance.

Estate Services have classified the various types of ventilation systems as follows:



Local CO2 Monitor Required

Mechanical – CO2 dependent

Mechanical systems with CO2 monitors fitted to the system that vary the flow rate of fresh air to maintain C02 levels below 1,000ppm in a space


Mechanical  - Constant rate

Mechanical systems that provide fresh air at a constant rate of 8-10l/s (sufficient to maintain C02 levels below 1,000ppm) per person assuming 100% occupancy


Naturally ventilated A

Areas where the calculation of window opening – floor space is in excess of that required under Technical Guidance Document Part F.


Monitors will be available on a rolling basis to assess CO2 levels in these spaces and to validate the adequacy of the natural ventilation as required.

Naturally Ventilated B

Areas where the calculation of window opening – floor space is in line with that required under Technical Guidance Document Part F but is not significantly over


Naturally ventilated work spaces that are at a distance from windows or external doors

CO2 monitors will be placed in the space to assess ventilation during use.

In addition monitors will be available on a rolling basis to assess CO2 levels in these spaces if required.  

CO2 monitors will indicate the real time level of C02 in a space. Levels will fluctuate as persons walk past the sensors or combustion activity outside of the building varies, e.g. due to traffic levels. However in line with best practice guidance the aim is to keep the CO2 levels at or below 1,000 ppm as much of the time as possible.

Remember, CO2 levels do not indicate the presence or absence of Covid material in a space, they are a way of validating one of the control measures (i.e. ventilation) that is used to help reduce the risk from Covid. The wearing of face coverings also helps reduce the risk by trapping many of the droplets and aerosols produced by the wearer preventing them entering the air breathed by others.

A CO2 alarm is an indicator of exhaled air in the area around the CO2 sensor. It is not indicative of Covid levels in a space nor does a CO2 alarm render a space as unsafe to work in. A CO2 alarm is indicative of poor ventilation in a room.

An ‘amber’ warning on a CO2 monitor means that CO2 levels in the room are over 1,000ppm. If an ‘amber’ alarm register then you should:

  • Ensure that persons have not congregated close to the sensor
  • Wait for short period of time to see if the alarm clears (returns to amber or green)
  • If the monitor remains in alarm make sure windows are open fully
  • If necessary open classroom door(s) temporarily to improve air flow

Experience to date has shown that this should be sufficient to reduce CO2 levels back below 1000ppm.

The types of local CO2 monitors in use in UCD and how they display CO2 levels and alarms are shown below.

Wall Mounted CO2 Monitor

A continuous ‘amber’ warning is not a reason to end a class but should be reported to Estates on ext. 7000 at the end of the class. If Estates cannot rectify the situation you may choose not to use the teaching space until resolved.

If elevated levels of CO2 are found on a consistent basis in a space then the use and occupancy of that space will be reviewed and if necessary modified.

CO2 levels will fluctuate at the start and end of class and as persons move around the CO2 sensor (your exhaled breath contains ~40,000ppm of CO2). Always allow time for an alarm status to return to ‘green’ before contacting Estates.

If you are concerned about ventilation in a space Estate Services can provide a CO2 monitor for a time to validate ventilation efficiency.

If the BMS detects elevated CO2 levels then the ventilation system will increase air flow / extraction rates if that functionality is available. If that automatic increase in ventilation rates is not available then Estate Services via BMS monitoring will send a resource to the classroom to check the CO2 levels on the ground and will ensure that the mechanical air handling system is working correctly.

If C02 levels remain elevated then Estate Services may request that the class be ended early so that a review can be carried out.

Estate Services have reviewed teaching spaces and rooms with poor ventilation have been modified or removed from use. In some cases the use of HEPA filtered air treatment units may be used in lieu of ventilation in some teaching spaces if an adequate level of filtration can be achieved. 

The provision of adequate ventilation will be the objective in all workspaces. However if there are spaces where this cannot be achieved the use of air purifiers will be considered if no alternatives are available.

In a naturally ventilated spaces:

  • You should ensure that all windows are opened fully and doors are also opened where practical. This may result in a reduced temperature in some spaces.
  • In a naturally ventilated classroom you can ensure that all windows and doors are open when leaving the classroom so the space can air

In mechanically ventilated spaces there is no need to open any windows or doors as the ventilation provided by the system is sufficient to achieve adequate air quality.

Most corridors and access spaces rely on natural ventilation. Where there are windows in these spaces these should be opened where possible.  

In a small number of instances these spaces are mechanically ventilated where fresh air is supplied into the space.

Corridors doors should be left open where possible, however it is important not to prop open any fire doors as this would contravene fire regulations.  Fire doors are easily recognisable as they will have a Fire Door Keep Closed label attached to the door. Some fire doors are fitted with special ‘door hold open’ devices (which automatically release/close the door when the fire alarm is activated). These should be left in the open position.

UCD Covid-19 Risk assessments information can be found here Covid-19 Risk Assessments

Contact UCD SIRC Office

University SIRC Office, Roebuck Castle, University College Dublin, Belfield, Dublin 4, Ireland.
T: +353 1 716 8771 | E: sirc@ucd.ie