Ventilation and the Use of CO2 Monitors – Guidance in the Updated Covid-19 Work Safely Protocol

In this blog I will review the new guidelines on ventilation and the use of Carbon Dioxide monitors in the government Covid-19 Work Safely Protocol.

The latest version of the Covid-19 Work Safely Protocol gives advice about the use of Carbon Dioxide (CO₂) monitors. This advice is outlined in Section D. Heating, Ventilation, and Air Conditioning (HVAC) of the protocol.

Can CO₂ monitoring help control Covid-19?

The risk of getting COVID-19 is higher in crowded and poorly ventilated spaces where infected people might spend long periods of time together in close proximity. CO₂ is contained in the air which people exhale and if they are infected, they may also exhale droplets containing the virus. Ventilation is a key factor for reducing the spread of Covid-19 in buildings and other enclosed spaces, e.g. vehicles. It helps to remove the virus from the air, thereby lowering the risk of airborne transmission.

Checking CO₂ levels may help determine if ventilation is poor in an area where people work. However, while checking CO₂ levels may be useful in a number of limited settings, they are less effective in work areas used by few people or in large workspaces. Ventilation can disperse infected air and CO₂ and therefore can reduce the risk of exposure to Covid-19.

It should be noted that CO₂ monitors do not measure levels of Covid-19 rather they indicate how effective your ventilation system is working. The use of CO₂ measurements as an indicator of building ventilation when there are CO₂ sources other than people, such as baking, brewing, dispensing carbonated drinks, fuel combustion (fires and stoves), and cooking is not recommended.

The Working Safely protocol indicates that checking CO₂ levels is not a good proxy for transmission risk in spaces where there is additional air-cleaning (e.g., HEPA filtration) as these remove the virus but not exhaled CO₂.
Additional research is needed to determine overall how levels of CO2 can provide a more reliable indicator to show that ventilation is adequate to mitigate transmission risks.

What is a safe level of CO₂?

CO2 outdoor air concentrations are approximately 400-480 parts per million (ppm). CO2 concentrations above 1400-1500 ppm are likely to be indicative of poor ventilation. If CO₂ concentrations are noted to increase towards indicative values of poor ventilation, then it is recommended that mitigation measures to either increase ventilation or decrease occupancy are taken. Generally, if the CO₂ level in a room exceeds 800 ppm, more should be done to improve the flow of fresh air.

The second report from the Expert Group on Ventilation who advised NPHET recommended sensors should warn when concentrations are between 800 ppm and 1,000 ppm and alarm when concentrations reach or exceed 1,000 ppm. CO₂ monitors should be CE marked and based on non-dispersive infrared (NDIR) technology and have a measurement range of 2,000 ppm. CO₂ monitors that have sensors that measure CO₂ equivalent or indirectly are not recommended. Always follow the sensor manufacturer’s advice and instructions on care and use of the sensor at all times and ensure adequate training is in place on their use and maintenance.

CO₂ monitors should never be used as a means to avoid adherence to the COVID-19 infection prevention and control measures recommended by Public Health.

The Working Safely Protocol outlines those other devices such as ozone-generating devices and air disinfection devices may present additional chemical-related hazards in the workplace and their use should be fully justified by an appropriate risk assessment. It is not recommended to use these devices in occupied spaces.

The Health and Safety Authority have developed a set of checklists to help employers in relation to guidance for the implementation of the Work Safely Protocol. Checklist No. 8 is particularly useful as it relates to ventilation (click here).

Where can I get further guidance on CO₂ monitoring?

• The HSE in the UK have developed excellent guidance on the use of CO2 monitors to identify poorly ventilated areas.
• The manufacturers’ manuals for the monitoring device will also be useful.
• The Expert Group on Ventilation which advised NPHET has produced two reports on the Role of Ventilation in Reducing Transmission of COVID-19 which can be downloaded here.
• The Covid-19 Working Safely Protocol is available here.
• The HSA Checklist No. 8 Ventilation – is available from the HSA website here.

The HSA advice is that ventilation is an important factor in reducing the risk of aerosol transmission indoors, where individuals may be in close contact, potentially for long periods of time and in poorly ventilated areas.

Ventilation will not stop the spread of COVID-19 on its own and that is why it is only part of a hierarchy of risk controls. It is not a substitute for other infection prevention measures, such as vaccination, physical distancing, cleaning, face coverings, maintaining good hand and respiratory hygiene, staying at home if feeling unwell, and working from home where possible.