Government Advisors Back CO2 Monitoring for Covid Ventilation Planning

Original Article In: H&V News by Neil Merrett (15th June 2021)

overnment advisory groups conclude that CO2 monitoring offers an accessible means of identifying potential ventilation issues, but should not be used as a direct measure of Covid-19 infection risk.

Carbon dioxide can offer a cost-effective means of identifying poor ventilation rates when trying to manage Covid infection risks, according to new findings from several government advisory bodies.

Findings published by the Environmental Modelling Group (EMG) and Scientific Pandemic Insights Group on Behaviours (SPI-B), which bring together a range of academic and medical experts to advise the government, have reiterated the importance of ensuring effective ventilation in buildings when planning for Covid-19, as well as ongoing IAQ monitoring.

The guidance paper, which is not peer reviewed, sets out evidence from a range of sources that supports its recommendations on the role that measuring CO2 levels can play in understanding where there may be a higher infection risks within certain environments.

It stressed that CO2 is carried within exhaled air and represents the fraction of air coming from individuals within a specific space. This can be a concern due to the growing evidence that suggests the virus can be transmitted in aerosols and large droplets exhaled by individuals carrying Covid-19, as well as on contaminated hands and surfaces.

Effective ventilation continues to be recommended by the HVAC trade bodies, as well as groups such as the EMG and SPI-B, as part of a range of controls to try and limit risks in enclosed spaces.  CO2 levels are identified in the latest paper as an important metric that can offer a basic means of understanding how effectively or not air is being refreshed within spaces.

However, the two bodies warned that CO2 was not in itself a direct measure of infection risk, or ventilation rates – but a useful indicator of where further action and risk mitigation might be needed.

The findings stated, “CO2 monitoring can be a cost-effective way of helping to identify spaces with high occupancy and/or poor ventilation and for actively managing ventilation in a space. It can be used to enable a good balance between ventilation, thermal comfort, and energy use.”

Guidance calls

Another major conclusion of the paper was that clearer guidance on how to introduce CO2 monitoring for industry and end users would be a welcome step to positively enforce improved ventilation procedures and occupant behaviours.

As a general principal, the report paper said a consistent CO2 reading of under 800ppm would likely indicate a space is well ventilated, although not an environment entirely free of Covid-19 risks.

Sustained higher CO2 values of over 1500ppm could meanwhile be seen as an indicator of either overcrowding or poor ventilation in an area that may require mitigating actions.

The guidance paper added, “Many factors influence the level of CO2 measured in a space so monitors should be used as a broad guide to the environment rather than to define specific ‘safe’ thresholds.”

The EMG and SPI-B said the cited evidence showed there was a high likelihood that ventilation can effectively reduce airborne transmission of Covid-19, but did not reduce risks via close range transmission through aerosols or droplets.

The advice paper added that ventilation that is delivered in line with current UK building standards was likely to ensure a lower risk for airborne transmission along with social distancing guidance.

One potential area of concern in the paper seen as needing further research was about a suspected lower level of awareness around the importance of ventilation among businesses and members of the public.

The paper stated, “The quality of ventilation across UK building stock is unknown. There is evidence to suggest that a wide range of building types are not adequately ventilated, especially in the winter months; this may be due to operation, maintenance, or design.”

It cites over 50 different sources of evidence from government bodies, academics and official journals.

The paper’s publication was welcomed by Graeme Fox, technical head of trade body BESA, as a reflection of the potential role IAQ monitoring can play when planning and managing covid-19 mitigation plans.