Martin Kriegel sometimes no longer understands the world. The rumor “Ventilation = virus-free” continues in the corona debate. But that’s bullshit. “Ultimately, it’s a simple equilibrium equation: we have an infected person, the mixture of viruses is there – this mixture can only be confined in the room, but it will never completely disappear.”
Even when you ventilate, the concentration is never zero. “The longer we are in a room, the more we breathe in,” emphasizes the head of the Hermann Rietschel Institute at the Technical University of Berlin. As a father of three daughters, Kriegel knows all levels of the L question – one daughter in daycare, one in primary school and one in high school.
Spahn took him to the press conference
On October 8, he was introduced to the public in an unknown role, a sort of “government fan”. The corona crisis has led to a demand for completely new experts and advisory bodies. Health Minister Jens Spahn (CDU) invited Kriegel to accompany him to the federal press conference, title of the event broadcast live on television: “The Corona Situation in the Fall”.
Spahn explained there that the AHA rules (distance, hygiene, everyday mask) would now be supplemented with the “L”. L for ventilation. To avoid the other L, a new lockdown with closed nurseries and schools. Spahn thought the topic could be discussed in detail.
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But after Kriegel’s explanation of how ventilation can reduce the viral load in school classes and companies in the fall and winter, the journalists were hardly interested in this.
“That other big topic came up,” says Kriegel. He has to think about it for a moment. Oh yes, the ban on accommodation.
Since Kriegel was appointed to the TU in 2011, he has expanded the research focus on air pollution. Since then, he and his team have been working more closely with medical partners such as the Robert Koch Institute and Charité. “Corona gave it all an enormous dynamic at the time.”
TU professor Martin Kriegel advises the federal government on ventilation issues Photo: imago images / Jürgen Heinrich
When the question recently arose as to why the entire cabinet should not have to be quarantined after Spahn’s corona infection, reference was made to the great distance in the international meeting room from the chancellery and the constant ventilation. The cabinet is currently meeting there. A minister told “Spiegel” that the Chancellor himself provided the corona protection in the room for 180 people. Now air is refreshed there seven times an hour.
Kriegel has not yet personally visited the Chancellor, but she too relies on his expertise. “Political interest is new to us,” he says. Now, after the autumn break, the litmus test comes with more than 12,000 new infections per day, especially in schools and nurseries.
Spahn and Chancellor Angela Merkel (CDU) want to keep it open. And rely on the expertise of Kriegel for this. “Normal normal use is not really possible. The fewer people there are in the room, the less they will become infected, ”says Kriegel.
Like cigarette smoke
Fans for a few hundred euros are a waste of money, they simply do not thin the air, the virus load remains too high. “With such a weak device, we reduce the risk by a few percent, but not significantly. The most important thing besides ventilation is the time you spend in the house. Because all the dirt accumulates in rooms.
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It’s like cigarette smoke. “The smoke also floats around forever and never completely disappears. Regardless of whether a ventilation system is running, you can smell it everywhere in a few minutes. The same goes for virus particles. “
To zero the concentration, you need massive amounts of air, which is practically impossible. An infected person would permanently bring in a new viral load, such as when blowing out smoke through aerosols.
Chancellor Angela Merkel is said to have personally provided for the regular ventilation of the closet room.Photo: imago images / Jens Schicke
Whether it is an air filter or shock ventilation: it is only a matter of dilution. “That is why it is wrong to say that the room is cleaned by supplying fresh air or filtered air. Only the amount of air that flows through a device or is supplied from outside is virus-free.
That only changes the mixing ratio of the air contaminated with viruses. “I don’t understand at all. Misleading curves are now displayed everywhere showing that the virus load is reduced by more than 90 percent in minutes. You only get clean air when there is no more infected person in the room,” says the 45- year old.
The federal government has now launched a 500 million euro funding program with the Federal Ministry of Economic Affairs. It provides grants for the adaptation and improvement of stationary air-conditioning systems (RLT). The financing amounts to a maximum of 40 percent of the eligible expenditure, with a maximum of 100,000 euros. “We have all learned that aerosols are crucial in the transmission of the coronavirus,” stressed Economy Minister Peter Altmaier (CDU).
Systems are funded where many and varying people meet: in lecture halls and schools, in theaters and museums, in communal meeting rooms and mansions.
The ventilation expert Kriegel worked with experts from the Robert Koch Institute and Charité, as well as the Berlin-Spandau health department, to calculate specific scenarios in detail. Ultimately, ventilation is like a mask, the risk of infection can only be reduced.
Kriegel calculates this with an example: “We do not want one infected person to infect more than another. (R value = 1). If 20 people meet and one infected person comes along, the chance of infection may be a maximum of five percent, so that at the end of the meeting no more than one person is infected. “
If people stay in the room for two hours, the amount of clean supply air must be 3000 cubic meters per hour. This is usually more than can be provided by ventilation or filtering devices. When the 20 people come together for three hours, the supply air volume should be 4500 cubic meters per hour (m3 / h).
If you want an even lower risk of contamination – for example one percent – then the example requires 15,000 m3 / h of supply air for a stay of two hours and 22,500 m3 / h for three hours.
Limit the number of people indoors and the amount of time they stay
However, many devices can only handle 1000 cubic meters per hour. Depending on the room, with such a room ventilation the chance of infection can possibly be reduced to 20 percent. “But that also means that if there are 100 people in the room, 20 more could be infected.” That’s why it’s so important to limit the number of people indoors and the time they spend there.
Operating regularly in schools cannot go well for long in the current situation. “Especially in the higher classes you can check whether two to three days a week face-to-face lessons are sufficient and the rest of the work is done digitally,” says Kriegel. “It’s always better to get through the winter with a compromise than to risk another lockdown.”