Can the CO2 Level in a Space, Determine the Ventilation?

Can the CO2 Level in a Space, Determine the Ventilation?

Charlie
2 minute read

Can the CO2 Level in a Space, Determine the Ventilation?

Measuring the CO2 level in indoor spaces, is a very useful technique, although it has some limitations. Outdoor CO2 level is about 400 ppm, and human exhaled breath contains about 40000 ppm of CO2. When air is exhaled in indoor places the CO2 concentration is increased rapidly.

Since accurate, affordable Co2 meters are available, measuring Co2 is the best way to get a sense of the amount of exhaled air in a space.

If you measure:

  • ~400-500 ppm: the level of ventilation is very good
  • ~800-1500 ppm: 1% of the air you are breathing has already been breathed by someone in the space. This can start to be risky.
  • ~4400 ppm: 10% of the air you are breathing has already been breathed by someone else. This is a very dangerous situation. Levels this high are commonly observed in densely occupied spaces with low ventilation such as many schools.

In well ventilated spaces, the Co2 level should stay below about 700 ppm to reduce COVID-19 infection risk. Co2 can be monitored with an affordable (~$150) meter as described below, which can be easily shared with many people.

The exact level considered “safer” for Co2 varies and we have seen various recommendations from 500 to 950 ppm. Choosing a general level like this is a compromise to make the method feasible and simple enough for many people. A key goal is to make clear that the many shared spaces with 2000 or 3000 ppm Co2 are unsafe, so that people realise that they have to take action to improve the situation there.

Surveying classrooms, offices etc. with a Co2 monitor can be useful to determine which ones may have the worst ventilation, and prioritising our actions there.

Mini Carbon Dioxide Monitor – TheatreCaps.com

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