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Corona pandemic at schools: air filters should reduce risk of infection – not all devices are suitable

Air purifiers against corona: reducing the risk of infection?

Researchers at Goethe-Unversity Frankfurt have investigated various mobile air purifiers. To do this, the team led by Joachim Curtius,

Professor of Experimental Atmospheric Research, set up four air purifiers in a school class of 27 students for a week. The air purifiers had a simple pre-filter for coarse dust and lint, as well as a class H13 HEPA filter and an activated carbon filter.

The result: air purifiers can reduce aerosol concentrations in a classroom by 90 percent in half an hour. “An air purifier reduces the amount of aerosols so much that in a closed room even the risk of infection by a highly infectious person, a superspreader, would be reduced very significantly,” Joachim Curtius sums up after a model calculation based on the measurement data. (Colds and Corona: Regular ventilation in winter helps prevent infections)

Air purifier against corona: sensible technical solution

A study by the German Federal Armed Forces in Munich also came to a similar conclusion. In the Munich study, Christian Kähler of the Institute of Fluid Mechanics and Aerodynamics tested a device with a large volume flow and high-quality H14 filters. According to the study, the room filter had a filter combination that ensures that aerosol particles with a diameter of 0.1 to 0.3 micrometers are separated from the room air by 99.995 percent. (Corona in asthma, COPD and diabetes: How dangerous is the condition for high-risk patients?)

“The results show that aerosol concentrations in a room 80 square meters in size can be reduced to low levels anywhere within a short period of time,” the authors conclude. Accordingly, certain air purifiers are a sensible technical solution for greatly reducing infection risks  from aerosols.

Air purifier against Corona: It depends on the filter

But not all air purifiers are equally suitable. Who plays with the idea of acquiring such a room air filter, should therefore inform themselves sufficiently before the purchase. For example, filters installed in ventilation systems tend to be less suitable. This is because the classic fine dust filters only separate about 50 percent of the aerosols.Better are so-called H13, H14 and ULPA filters. According to aerosol researcher and head of the Hermann Rietschel Institute at the Technical University of Berlin, Martin Kriegel, these filters clean the air almost particle-free.

Air purifiers against corona: also suitable for schools?

The filters could also be a possible alternative for schools. Hesse’s state government, for example, has already announced that it will support school authorities with ten million euros for the purchase of air purification devices. “These are to be purchased in particular for classrooms where it is not possible to ventilate sufficiently because, for example, windows cannot be opened,” explained Education Minister Alexander Lorz (CDU).

Experts from the Federal Environment Agency take a rather critical view. Hence, the Commission for Indoor Air Hygiene continues to advise classic ventilation. In a detailed statement, it says: “The highest possible supply of fresh air is one of the most effective methods of removing potentially virus-containing aerosols  from indoor spaces.” The conclusion: mobile air purifiers in classrooms or at home cannot replace active ventilation, but at best act as a supplement in individual cases. (Ventilation against coronaviruses: Can air purifiers reduce the risk of infection?)

Mit Luftreinigern gegen die Corona-Pandemie: Sinnvolle Ergänzung zu regelmäßigem Lüften in Schulen? | Leben & Alltag (