Why ventilate?

Why is regular air exchange in classrooms important?

Classrooms should always be ventilated regularly. During ventilation, fresh air flows into the room and replaces the stale air. This removes moisture from the room, which reduces the risk of mold growth. In addition, fine dust, odors and vapors from e.g. furniture or cosmetics are removed. Last but not least, CO2 is removed to the outside, which can make people tired and reduce concentration.

Due to the comparatively low air volume in the classroom with many students present, the probability of infectious particles accumulating in the room is comparatively high. How likely infection is depends on several factors: How many people are in the room and how active are they, how large is the room, how often is the air in the room exchanged, what ventilation is available. Since the vast majority of schools in Germany do not have central ventilation systems, ventilation through the windows is the best and often the only way to get fresh air into the classroom.

How does proper ventilation work in everyday school life?

To protect against infectious particles, the air should be changed three times per hour. This means that the room air is completely exchanged for fresh air from outside three times per hour. This is ideally achieved as follows:
Ventilate every 20 minutes with windows wide open during class. All windows must be opened wide (shock ventilation). The greater the temperature difference between inside and outside, the more effective the ventilation. Therefore, when the outside temperature is cold in winter, airing for about 3-5 minutes is sufficient. On warm days it is necessary to ventilate longer (about 10-20 minutes). In hot weather conditions in midsummer, when the air temperatures outside and inside are similar, the windows should remain open continuously.

In addition, airing should be done after each class for the entire duration of the break, even during the cold season.
Even better than shock ventilation is cross-ventilation. This means that opposite windows are opened wide at the same time. In schools, cross-ventilation can also be accomplished by wide open windows on one side and hallway windows on the opposite side.

During both shock ventilation and cross ventilation, the temperature in the room drops only a few degrees. After closing the windows, it quickly rises again.

What is the use of CO2 traffic lights and how do I use them correctly?

Carbon dioxide (CO2) is a good indicator of "stale" air because everyone exhales CO2. In enclosed spaces and with larger numbers of people, such as classrooms, CO2 can quickly accumulate in the room air without ventilation. Excessively high CO2 levels cause fatigue in those present. An increased CO2 concentration does not allow any statement about virus-containing aerosols, but it does indicate that the room has not been ventilated for too long and therefore the risk of infection may be increased.

CO2 traffic lights are measuring devices for determining the concentration of CO2 in indoor air. They indicate the air quality in terms of CO2 via the indicator colors green-yellow-red. Some devices also display the concentration measured in parts per million (ppm). Up to 1000 ppm, the indoor air quality is considered good (green). If this concentration is exceeded, the traffic light switches to "yellow" and usually to "red" for more than 2000 ppm.

The devices are best placed at breathing height (approx. 1.5 m for seated persons) and in the center of the room. Positioning them near windows or placing them directly along a wall or facing a hallway is not advisable. It is not absolutely necessary to permanently install a CO2 traffic light in every classroom. Rather, it is sufficient if ventilation behavior is first rehearsed in a room with the help of the traffic light, which is then maintained even without the traffic light. The CO2 traffic light can then be used in the next classroom.



Source: Federal Environment Agency
Presidential Department / Press and Public Relations, Internet
Wörlitzer Platz 1
06844 Dessau-Roßlau