CO2 – COVID-19 Far Field Aerosol Transmission Involvement
The role of CO2 level measurement as an indicator of a Problematic Environment.
The Interaction of Multiple Factors appear to
affect virus transmission:
- Viral emission rate
- Ventilation rate
- Exposure duration
- Environmental conditions
- No. of occupants
SAGE  Recommendations:
- Continual CO2 monitoring should be part of that ventilation design and maintenance solution.
- Multi-occupancy spaces that have CO2 levels above 1500ppm should be prioritised for improvement.
- Spaces with enhanced aerosol generation such as gyms, concert venues, places of worship should be below 800ppm CO2.
- High CO2 Levels can indicate too many occupants are contained within a single area or space.
- Low temperatures and humidity create an enhanced risk, with temperature and humidity measurement a key indication
In the context of SARS-CoV-2 transmission, measurement of CO2 may be used as an indicator of poor ventilation.
In single-zone spaces with more than 20 people, a CO2 level that is regularly above 1500 ppm (absolute value) is likely to indicate ventilation conditions that pose a higher risk of aerosol transmission.
Spaces where there is potential for high aerosol generation should aim for CO2 at least below 800 ppm, and even this may not be sufficient to mitigate transmission (medium confidence).
In low occupancy or large volume spaces there is much greater uncertainty in CO2 measurements, therefore a low level of CO2 cannot necessarily be used as an indicator that ventilation is sufficient to mitigate transmission risks (medium confidence).
CO2 is not a good proxy for transmission risk in spaces where there is additional air cleaning (filtration or UVC) as these strategies remove virus but not exhaled CO2. It is a less reliable measure in spaces with low occupancy or very large spaces.
Measurement of CO2 should be carried out in the occupied area of a room with the sensors located away from windows,doors and ventilation grilles.
CO2 cannot be used as a proxy for ventilation in spaces where there are other CO2 sources present (e.g. combustion devices).
Measurement should normally be made over a period of at least 1 hour to ensure a representative reading. Sensor placement and accuracy must be taken into account when analysing measured data.
Continuous CO2 monitoring is not likely to be a reliable proxy for transmission risk in most environments. However preliminary research suggests that in spaces where the same group of people regularly attend (e.g. offices, schools), continuous monitoring may be possible to use as a transmission risk indicator.
CO2: if you can’t measure it you can’t manage it..
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