The Scientific Advisory Group for Emergencies (SAGE), in the UK, published a comprehensive paper on the role of ventilation in the transmission of COVID-19.  The document approaches multiple aspects of ventilation, summarizes related research, and provides recommendations and statements with a corresponding level of certainty.   SAGE continues to update this document with a recent release on October 23rd, 2020.

Excerpts from the document include:

• Ventilation is an important factor in mitigating against the risk of far-field (>2m) aerosol transmission, but has no impact on other transmission routes (high confidence). The importance of far-field aerosol transmission is not yet known, but evidence suggests it is a risk in poorly ventilated spaces (medium confidence). (2m = 6.56 feet)
• Activities that may generate high levels of aerosol (singing, loud speech, aerobic activity) are likely to pose the greatest risk; in some spaces even enhanced ventilation may not fully mitigate this risk (medium confidence).
• Multi-occupant spaces that are used regularly and are poorly ventilated (below 5 l/s/person or above 1500ppm CO2) should be identified and prioritized for improvement. (5 l/s = 10.6 CFM)  (ppm = parts per million)
• There is currently no evidence for far-field aerosol transmission in well ventilated spaces (medium confidence)
• Under steady state well-mixed conditions for the same duration, models suggest that exposure to aerosols approximately halves when the ventilation rate is doubled. This effect means the benefits of increased ventilation are most significant where ventilation rates are low (high confidence).
• On average doubling the occupancy may result in a four-fold increase in the probability of far-field aerosol exposure.
• 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).

Click here to access the complete document – EMG: Role of ventilation in controlling SARS-CoV-2 transmission, 30 September 2020

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