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Scientific foundations

Decades of research have shown the importance to health and safety of ventilation in public spaces. We recognise the importance of all available barriers in the defence against airborne pathogens such as the SARS-COV-2 virus but our focus is on ventilation  –  the key, but often ignored defense against disease transmission. Proper ventilation ensures the circulation of clean air through an indoor space, thereby clearing out pollutants. Assessment includes measuring carbon dioxide concentrations in specific areas of occupied indoor spaces as it has been shown that the carbon dioxide levels are a good proxy for the levels of other possible contaminants in the air. GreenFlag certification is issued if ventilation controls are adequate.

Very few Covid-19 infections are linked to the fomite route (spread by contact). Aerosol transmission of Covid-19 is by far the most important route of transmission. Virus-laden aerosols infect susceptible contacts in close proximity where they are most concentrated- like smoke. Infection of individuals at a distance greater than 1-2m is also common in poorly ventilated spaces.

Why use ventilation as the cornerstone criteria for GreenFlag certification?

  • Ventilation is the most neglected barrier to the spread of disease
  • 25% of COVID-19 infections are linked to the fomite route
  • Studies show lower transmission infections attributed to the fomite route (about 16%)
  • Aerosol transmission of COVID-19 is probably the most important route of transmission
  • Virus-laden aerosols frequently infect susceptible contacts at close proximity where they are most concentrated — like smoke
  • The main “universal” barriers to transmission in public spaces now importantly include ventilation

CO2 is a surrogate for estimating Covid-19 infectious dose in an occupied space

High indoor space CO2 levels correlate with other measures of poor indoor air quality, and are linked to increased absenteeism, loss of productivity and poor decision-making.

Green Flag CO2

  • CO2 measured in parts per million (PPM) is a measure of ventilation status of an indoor space

  • 800 parts per million CO2 roughly equates to a fresh air ventilation rate of 15 liters per second per person

  • A CO2 value maintained less than 400ppm above ambient (outside) air limits viral transmission (99.9% risk reduction)

  • Outdoors, CO2 measures about 420 PPM. Any additional CO2 in an indoor space is usually generated by occupants of that space

Ventilation is the “universal” barrier to transmission in public spaces is ventilation.

Air change rates required to maintain a given CO2 concentration in a typical office with 20 people breathing normally.
Air change rates required to maintain a given CO2 concentration in a typical office with 20 people breathing normally.