Air Quality and Infection Risk
A basic function of ventilation
People exhale CO₂ and enrich the indoor air with it. Therefore, an important function of ventilation is to remove this CO₂ again. According to a recommendation dating back to the hygienist Max von Pettenkofer (1818-1901), which is still used as a guideline today, the CO₂ concentration in indoor spaces should not exceed 1000 ppm. To comply with this, 20 m³ or more of room air must be exchanged for fresh air every hour per person in the room, depending on their level of activity and constitution.
Comparison with infection protection
For example, if there are 30 people in a room with a volume of 200 m³, i.e. a typical classroom, 600 m³ of fresh air is required per hour to remove the exhaled CO₂. Thus, the room air must be replaced every 20 minutes. In this particular case, this is exactly in line with the Federal Environment Agency's (UBA) recommendation to exchange air in classrooms every 20 minutes due to infection control. However, the infection control recommendation applies regardless of the number of people in the room.
In another example, 5 people meet for a game night in a living room with 50 m³ volume. For good air quality with 5 people, 100 m³ of fresh air is needed every hour, so the room would have to be thoroughly aired every half hour. Usually this does not take place and the air quality then becomes very poor during the evening. In order to prevent infection, the air in this smaller room should be changed every 10 minutes. If, on the other hand, the room remains unventilated for several hours, then extremely high doses can be transmitted in the event of infection, because the dose increases with the square of time without ventilation. At times when there is a risk of infection via indoor air, gatherings in small rooms are therefore not recommended unless there is permanent, very good ventilation.
The graph shows the recommended air change interval for the purpose of infection control as a function of room volume. The number of people in the room does not affect the recommendation! More info and a description of the risk estimation method used here are included in the video.
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by D. Hennings • www.eclim.de • under CC BY-NC-ND