Corona virus: Are air-conditioning and air-conditioning systems thrown by viruses?

Our reader Stefan Steinbach from Aachen asks: "Can viruses be transmitted by air conditioning or air circulation systems, for example in supermarkets or similar buildings?" The answer from Almut Cieschinger, documentary at SPIEGEL:

That is not excluded. However, according to experts, spreading is only possible if the system has not been well planned and maintained. Sars-CoV-2 gets from one person to the next via droplet infection, for example when coughing or sneezing. The virus can also be transmitted indirectly, for example by coughing up an infected person and touching an object that someone else touches. This transmission path is called smear infection. However, transmission through the smallest virus particles in the air also seems possible, because according to a first, not yet fully verified, US study, the coronavirus could also be infectious in aerosols for up to three hours.

In this respect, it is theoretically conceivable that it could also be distributed in rooms by ventilation systems or get from one area to the next and infect people there. For example, it is assumed that in 2003 after the outbreak of the Sars epidemic in a Hong Kong residential complex, the virus had spread due to defective floor drains and exhaust fans. More than 300 people became infected there, more than 30 died. Most recently, the cruise ship "Diamond Princess" made headlines, which had been quarantined in the Japanese port of Yokohama with numerous corona-infected passengers. Among other things, there is a suspicion that the virus was able to spread through the central ventilation system.

A properly installed and maintained ventilation system can also make it more difficult for the virus to spread, on the other hand, if used air in the rooms is quickly removed and replaced by air from outside or at least highly enriched. If systems are installed in the ventilation system that render the particles harmless or filter them out, the concentration of virus particles can even decrease significantly. However, virus-sensitive particle filters, so-called hepa filters, are usually used primarily in hospitals or laboratories. However, even coarser filters can significantly reduce the particle load of viruses in the air, according to three German building equipment associations.

According to the Federal Environment Agency, the effectiveness depends on the planning and maintenance of the systems: "If the air is routed separately, so that the air extracted in one room is only in indirect contact with the supply air via a heat exchanger and cannot get into other rooms no risk of virus transmission in the building. " Incorrect planning or maintenance could, however, result in "incorrect flows" which lead to exhaust air from one area of ​​the building being supplied to another area of ​​the building as supply air. The three German trade associations also almost exclude this: The systems would be operated under negative pressure, which would allow "no exhaust air" to escape even if there were leaks in the pipes.
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