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Corona: Air filtration equipment for daycare centers and schools

The city administration will order mobile air filtration devices for all classrooms and childcare rooms in daycare centers and schools in Bonn that cannot be adequately ventilated, in order to reduce the risk of infection with the corona virus. The mobile units are only a temporary solution. In the long term, the rooms are to be equipped with a permanent supply and exhaust air system. The administration intends to take advantage of funding opportunities announced by the federal and state governments for both.

I very much welcome the decision of the crisis team to purchase mobile air purification devices for 150 rooms and thus for all category 2 rooms in schools and daycare centers," explained Mayor Katja Dörner. "The mobile devices are a good interim solution until we have the more sustainable solution of permanently installed supply and exhaust air devices."

Against the backdrop of the infection events in the wake of the Corona pandemic and the conflicting statements on the risk of infection for children and young people, it was necessary to clarify the extent to which daycare centers and classrooms can be adequately ventilated and thus minimize aerosol exposure and the risk of infection for children, students and teaching and educational staff.

TÜV: High air exchange rates in examined rooms

At the end of April, the Municipal Building Management of the City of Bonn (SGB) commissioned TÜV Rheinland Energy GmbH (TRE) to assess whether the use of air purifiers in schools and daycare centers can contribute to better protection against infection or whether it is necessary.

Three schools and one daycare center were selected and examined: the Tannenbusch school center, the Marienschule, the Heinrich-Hertz-Europakolleg and the Gerhard-Hauptmann-Straße daycare center.

In each case, three rooms were examined under typical usage and ventilation conditions, for example windows or skylights in the tilt position or fully open and additionally with open doors. The air exchange rate and the necessary outdoor air volume flows were determined.

The TÜV came to the conclusion that, with one exception, high to very high air exchange rates were present in the rooms examined under the conditions described. Due to the high air exchange rate, mobile air cleaners are therefore not absolutely necessary from a hygienic point of view. However, mobile air cleaners that separate aerosols and virus particles from the aspirated room air via Hepa filters can reduce the virus load.

All the rooms investigated, with the exception of a basement room with skylights in the Heinrich Hertz College of Europe, were adequately ventilated. For this basement room, which had already not been used in the previous school year, and similar other rooms, purely manual ventilation is not sufficient from an infection hygiene point of view, and here the use of air purifiers could provide better air from a hygiene point of view. However, air purifiers alone can only improve the air quality, which deteriorates over time during teaching, to a limited extent with regard to the viral load. Furthermore, they have no influence on the CO2 concentration in the room. This can only be reduced by supplying fresh air.

Ventilation still essential

Since air purifiers cannot replace ventilation, the TÜV refers to a ventilation plan with regulated ventilation measures, to which the Federal City of Bonn regularly refers. The Federal Environment Agency (UBA) has also published such a plan.

Briefly summarized, it provides for the following:

Shock ventilation every 20 minutes for 3 to 5 minutes in winter and 10 to 20 minutes in summer. 
airing during all breaks
cross-ventilation if possible. 
During shock and cross ventilation, the room temperature drops by only a few degrees and rises again quickly after the windows are closed.

In addition, if CO2 concentrations are high, measurements with CO2 traffic lights could indicate the need for additional ventilation measures.

Federal Environment Agency classifies rooms in daycare centers and schools
For its part, the UBA has issued classifications of school and kindergarten rooms, dated July 17, 2021. Based on these recommendations and the results of the TÜV expert reports, the SGB has again reviewed and assessed the approximately 2,770 school rooms used for teaching or care and the daycare center rooms in the short term.

According to the results, around 2,640 rooms in schools belong to category 1 and can be used without any further technical measures. These rooms are either equipped with a ventilation and air-conditioning system or the windows can be opened to such an extent that the rooms are adequately ventilated.

117 rooms correspond to category 2 with limited ventilation possibilities. Rooms are classified in Category 2 if the windows can only be tilted or if ventilation flaps with a minimum cross-section and no ventilation system are present. While a good four percent of classrooms in Bonn are classified as Category 2, the Federal Environment Agency found in July of this year that the figure in two German states was between 15 and 25 percent.

Eleven rooms are classified in category 3. These are not to be ventilated. Like the basement room in the Heinrich Hertz College of Europe, they cannot be used until further notice. 

For the Kitas, the result of the inspection is that the rooms of the vast majority of Kitas are well ventilated and can be used without restrictions. "In probably three Kitas, 20 rooms have to be assigned to category 2 according to the current status. In the short term, we want to install air purification devices in these 20 rooms and, for a long-term solution, we want to examine the installation of fixed supply and exhaust air devices," says Lutz Leide, head of the Bonn Municipal Building Management.

By far the largest part of the rooms can be ventilated well

"I am very relieved that by far the majority of the rooms used by our children and young people are sufficiently and well ventilated," said Carolin Krause, Assistant Secretary for Schools, Social Affairs and Youth. "We are far below the state average for the small number of rooms in Category 2. That's gratifying."

"The rooms in Category 2 have also been examined in the past to see whether further improvements in the ventilation situation can be achieved through simple structural measures," Leide continued. Rooms where this is not and was not possible are to be given priority for a supply and exhaust air system. These are supply and exhaust air systems in skylights, for example, or permanently installed systems with ventilation to the outside.

Experts: Devices do not replace known hygiene measures

Professor Dr. Martin Exner, former director of the Institute of Hygiene and Public Health and executive director of the Center for Infectiology and Infection Control at the University of Bonn, and his successor in office, Professor Dr. Nico Mutters, see air purification devices as only part of the necessary measures to prevent SARS-CoV-2. They emphasize that the devices cannot replace the other measures, such as ventilation, AHA+L rules, masks, testing and vaccination, because they do not provide the necessary supply of fresh air. Professor Exner said, "Regular ventilation must continue, and the hygiene rules we learned during the pandemic must be consistently followed."

Professor Exner recalled that an outbreak occurred at a daycare center in Beuel, even though three mobile air purification units were in use there.

The professors, who advise the crisis team of the Federal City of Bonn, also prefer the installation of simple exhaust fans in skylights in category 2 rooms as a sustainable solution. The deputy head of the crisis team, city treasurer Margarete Heidler, therefore reaffirms the administration's plan to install exhaust and supply air systems in classrooms in the long term with financial support from the federal and state governments.

Concrete promotion conditions of federation and country are still missing
The state and federal governments have announced that they will fund both the necessary air filtration equipment and construction measures. However, the concrete funding requirements for the procurement of air filter units are still missing. Information on this has been announced for the near future. Nevertheless, the crisis management team of the Federal City of Bonn has decided to launch the tender for the procurement of the equipment now, as longer delivery times are to be expected due to the high demand. The administration assumes that the subsidies will then also flow for the purchased devices.

Mobile air purification units that meet the requirements currently cost around 3,000 euros plus any installation and maintenance costs. At the same time, further planning for structural installations is being carried out. According to current knowledge, each permanently installed exhaust and supply air system will cost around 15,000 euros plus planning, installation and maintenance costs.

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