Carbon dioxide monitors in education settings

This guidance sets out how education settings can use carbon dioxide monitors as an aid for the management of ventilation. The guidance should be read in conjunction with the decision framework and risk assessment for your location.

The requirement to take reasonable measures applies in a very broad range of circumstances, including every kind of workplace that is open. This includes, for example: 

• public services
• health and social care premises
• schools and childcare settings
• higher education and further education  settings (including training centres and adult learning)
• call centres
• hospitality businesses
• travel and holiday accommodation
• voluntary services
• commercial and industrial premises
• construction sites and other open sites such as roadworks and outdoor places (including livestock markets)

The duty in law to take reasonable measures applies to the person or persons responsible for premises open to the public and on the person responsible for the work being undertaken in any workplace (that is the person responsible for management control of the premises).

It is the responsibility of those in control of premises (such as headteachers or principals) to ensure good levels of ventilation are maintained in buildings. For schools, local authority estates and corporate health and safety teams should be contacted for support. Colleges and universities should work with their estates or facilities management and corporate health and safety teams. For non-state maintained childcare settings, owners should work with their own health and safety advisor and facilities management provider.

Good ventilation can help reduce the risk of spreading airborne viruses, so a focus on improving general air flow, preferably through fresh air or effective mechanical systems, can help to create a safer environment for staff and learners. You can generally maintain and increase the supply of fresh air by simply opening windows and doors, although internal fire doors must remain closed unless connected to a device that causes them to self-close upon activation of the fire alarm.

People exhale carbon dioxide when they breathe out. If there is a build-up of carbon dioxide in an area it can indicate that ventilation needs improving. You can use carbon dioxide monitors to help you:

• identify areas of poor ventilation
• gauge how much you need to open the windows or improve mechanical ventilation (including air conditioning)

It is important to remember that carbon dioxide monitors are an indicator of ventilation status and not infection risk.

There are many different types of carbon dioxide monitors available. The most effective portable devices to use are non-dispersive infrared (NDIR) carbon dioxide monitors. This was the type provided by the Welsh Government to state-funded education settings over the autumn term 2021.

The monitors allow for assessment of ventilation in spaces and informs the setting's risk assessment with regard to ventilation.

The carbon dioxide monitors provided by the Welsh Government are Rototherm AM60 units. This guidance should be read in conjunction with the instruction manual provided with the units.

Other carbon dioxide monitors may be used to follow this guidance but care must be taken to ensure any differences in units are taken into account.

Estates or facilities management teams must ensure carbon dioxide monitors are maintained and calibrated in accordance with the instruction manual provided.

Carbon dioxide monitors are best suited to spaces that are densely occupied for approximately one hour or more.

In education and childcare settings this includes, but is not limited to:

• teaching spaces (including lecture rooms, classrooms and practical teaching spaces)
• indoor play spaces (for example rooms in nurseries)
• staff rooms, large offices, meeting rooms, group or breakout rooms

Monitoring is not recommended for use in areas where carbon dioxide monitors are unlikely to give reliable readings, including:

• large, open internal spaces and spaces with higher ceilings, such as sports halls or atriums
• spaces that are densely occupied for shorter periods, such as corridors or lobbies
• areas with low occupancy density including kitchens and toilets, or offices with one or two occupants

Rooms that already have carbon dioxide monitoring integral to their building management system may not require additional standalone monitors. Your estates or facilities management team should know if monitoring is already in place.

Placement

When deciding where to place monitors, you should initially prioritise spaces that feel constantly stuffy or have a persistent smell as these are likely to be under-ventilated. Using a monitor in these spaces first can help you prioritise action effectively. You should place carbon dioxide monitors:

• at head height when seated
• away from ventilation outlets, such as grilles or windows
• at least 0.5 m away from occupants (closer than this could give inaccurate readings)

If your measurements in an occupied space seem very low (far below 400ppm) or very high (over 1500ppm), it’s possible your monitor is in the wrong location and you should move it to another location in the space to get a more accurate reading.

Monitors should be placed where the display can be seen by a member of school staff so that they can identify if the display colour changes to amber or red.

Measuring

• After 3 minutes' warm-up the monitor provided by the Welsh Government will be ready for use.
• When to measure: depending on how the room is being used, staff should check the measure shown on screen at the beginning of class and at the end and monitor this. Staff may wish to check midway if, for instance, the class is over an hour duration. There should be no need to interrupt a lesson to take a reading.
• You may also wish to monitor more frequent measurements in situations whereby the 1500ppm is observed to be exceeded frequently. These measurements will help inform the average carbon dioxide levels across the day.
• Measuring need only be carried out in occupied rooms.

Rotation of monitors (if required)

You can rotate monitors around the building and the spaces that are suitable for monitoring, so that you can identify ventilation needs across your setting. Rooms should be monitored for at least one full day before rotating them to a different space. You can keep your rota simple: start with potentially under-ventilated rooms as set out above and then move your monitors to other rooms (prioritise those most used or with the highest occupation density).

If you find that rooms are consistently well ventilated there is no need to continue keeping them on your rota for monitoring carbon dioxide levels unless occupancy or use of room is changed. If placed in a new room, the monitor might need to refresh (produce a new measure) a few times before settling on a new reading.

The amount of carbon dioxide in the air is measured in parts per million (ppm). A consistent value under 800ppm, indicated by a green light, does not require any action and implies that a space is well ventilated. Background ventilation should still be provided in order to maintain good air quality.

A value over 800ppm indicated by an amber light should be seen as an indicator of inadequate background ventilation and a need to increase the ventilation further. If not done so already, you should start to improve ventilation by simply opening windows and doors (fire doors must remain closed unless connected to a device that causes them to self-close upon activation of the fire alarm) or by increasing the levels of mechanical ventilation.

A consistent value of over 1500ppm carbon dioxide concentration indicated by a red light in an occupied space is an indicator of poor ventilation. You should take action to improve ventilation where carbon dioxide readings are consistently higher than 1500ppm as described in the Improving ventilation section.

In summary

Less than 800 PPM

• No action required as this is an adequate level of ventilation.
• Continue monitoring.
• If levels start to increase this is an early indication that ventilation may need to be increased.
• Always maintain background ventilation.

800 PPM to 1500 PPM occasionally

• Increase ventilation by simply opening windows and doors (fire doors should not be left open unless connected to a device that causes them to self-close upon activation of the fire alarm).
• Purge the air before and after each lesson by simply opening all windows and doors fully for up to 10 minutes.
• Limit learner numbers where possible.
• Move high-level activities such as dance, music or physical activities to well-ventilated spaces.

800 PPM to 1500 PPM consistently

Report to estates or facilities management or to the person responsible for the building that they need to:

• increase the rate delivered by mechanical ventilation (including air conditioning) units to help to optimise the efficiency of them (this is likely to reduce running costs)
• extend timings of mechanical ventilation (including air conditioning) units to purge the air before and after lessons
• check and clean all local mechanical ventilation
• consider whether additional measures or interventions could help

Over 1500 PPM

• Consult with estates or facilities management, or the person responsible for the building to consider introducing additional mechanical or natural ventilation best suited to the individual location.
• Purge the air as soon as possible.

Remember to look out for consistently high values: Because many factors influence the level of carbon dioxide measured in a space, a single snapshot reading is unlikely to be reliable. We therefore recommend waiting for 5 minutes before retaking a high reading, to allow for the monitor to settle. Measurements within a space can vary during the day due to changes in numbers of occupants, activities or ventilation rates. Doors and windows being open or closed can also have an effect.

Instantaneous or ‘snapshot’ carbon dioxide readings can be misleading, so you should take several measurements throughout the day to represent changes in the use of the room or space. Then calculate an average value for the occupied period.

You may need to repeat monitoring at different times of the year as outdoor temperatures change as this will affect when you can open windows and doors if your space relies on natural ventilation.

Your readings will help you decide if a space is adequately ventilated.

The use of carbon dioxide monitors and any associated risk assessments for ventilation should be taken in conjunction with Welsh Government’s published 'Local COVID-19 infection control decision framework for schools from autumn 2021: impact assessment'.

Your setting's risk assessment should cover identification of any poorly ventilated spaces, including through the use of carbon dioxide monitors if available. If you do not already address ventilation in your assessment, you should add this as soon as you receive your carbon dioxide monitors.

You should consider in your risk assessments the potential for certain activities to affect carbon dioxide levels, for example:

• singing
• shouting
• physical exercise
• use of a gas appliance for cooking
• Bunsen burners in science labs

You should note that health and safety law states that employers, including education and childcare settings that are the employers for their settings, must take reasonable measures to ensure there is an adequate supply of fresh air (ventilation) in enclosed areas of the workplace.

Where carbon dioxide readings are between 800ppm and 1500ppm small interventions such as opening windows and doors should be adequate to bring levels below 800ppm. High-level open windows will provide ventilation without causing draughts. It is important to remember that a small amount of continuous background ventilation should always be maintained, even when monitors display levels below 800ppm.

Other local interventions to consider include:

• purging the air in the classroom before and after each class or lesson by opening all windows and doors fully for up to 10 minutes
• providing better air flow circulation by having doors or windows at opposite ends or sides of classrooms open rather than just one or two centrally
• limiting learner numbers where possible
• providing comfort breaks during longer lessons (in further or higher education)
• moving activities such as dancing or singing to larger or better-ventilated spaces
• remedying as soon as possible through your estates or facilities management (or in the case of schools,  your local authority) windows that are sealed or difficult to open, or air vents that are blocked

Where readings still remain between 800ppm and 1500ppm despite local interventions you should consult your estates or facilities teams (or person responsible for the building) to consider:

• ensuring regular maintenance (including filter changes) and running of mechanical; ventilation (including air conditioning) to optimise the efficiency (this is likely to reduce running costs)
• extending timings of mechanical ventilation (including air conditioning) to purge the air before and after lessons
• checking, cleaning and increasing ventilation rates of all local mechanical ventilation (including air conditioning)
• whether additional measures or interventions could help

Additional ventilation, mechanical or natural, should be considered if the readings are consistently over 1500ppm. Your estates or facilities teams (local authority for schools) should advise on the best solution to each individual case. In the interim, you should consider moving to other rooms, repurposing space elsewhere in the estate or limiting numbers.

Levels of above 1500ppm are a sign of poor ventilation and should be addressed as part of your workplace or teaching space assessment.

Care needs to be taken of draughts from open windows or doors causing hazards, particularly in science and design and technology classrooms in secondary schools. Having doors open may pose safeguarding and security issues. Purge ventilation between lessons or mechanical ventilation may be required for such areas, and form part of the school’s risk assessment.