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It was an announcement that made people sit up and take notice: “DLR is investigating the spread of viruses in planes and trains,” announced the German Aerospace Center (DLR) on May 27th.
It was two months ago that Germany went into lockdown because of the corona virus.
But little was still known about the disease and how it is transmitted.
The study that DLR and Deutsche Bahn (DB) wanted to carry out jointly was intended to remedy the situation.
"The first results of the recently started research can be expected in the coming weeks," it said at the time.
But then it happened for a long time: nothing.
In the summer, when asked at the DLR, the publication was delayed, the questions were explosive and they did not want to publish premature interim results.
They asked for patience until the end of the year.
At Deutsche Bahn, it is now denied that the publication had been postponed, the publication of interim results was never planned.
On Wednesday evening, nine months after the start of the pandemic, the time had come: “Study by DLR and DB shows: mouth and nose covering works,” said the research center.
At the same time as a press release, DLR published a “short version” of the study on the Internet.
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But the knowledge that can be found in it is poor.
"The tests carried out on the test vehicle show that the spread of aerosols and droplets within the passenger compartment mainly takes place directly and over a limited distance."
In other words: the closer you sit in the car to an infected person, the greater the virus load.
"A virological assessment of possible infection risks was not part of the investigation," it continues.
The study leaves the key question unanswered: How dangerous is a journey on the train?
If you take a closer look at the "short version", you can see that it only contains individual results, others have been left out.
In some cases, they are also interpreted to a very large extent, although the measurement data does not actually provide that, and experts also criticize the test setup.
Source: WORLD infographic
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The researchers carried out two different series of tests for their study: In the first, an artificial CO2 source was placed in 63rd place of an ICE car and then measured how much of the gas was still reaching the surrounding seats.
The fine aerosols behave very similarly to the gas.
In the second test setup, a generator did not emit any CO2, but rather larger particles of “artificial saliva”, which can also be found in a person's breath.
The result was not surprising: In the CO2 experiment, the place next to the infected person was the most heavily used.
The researchers defined the concentration directly at the source as 1. On the neighboring square it was still almost as high at 0.96.
Large parts of the gas (0.51) also reached the row of seats behind.
On the other side of the corridor, the concentration was also high at 0.41, and even two rows behind the source, the researchers measured a value of 0.3.
The values in the next row of seats further forward, which is placed at a table directly opposite the source, were also increased.
Here the values were between 0.21 and 0.28.
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The only problem is: These values say nothing at all if you don't know at what concentration there is a risk of infection.
Is 0.21 enough for this or does the concentration have to be significantly higher?
"A virological assessment of the risk of infection was not the subject of the investigations," said the railway.
“In this regard, the study lays the foundation for further scientific research and a virological evaluation of the results.” Nine months after the start of the pandemic, the basis for a virological examination is now available.
After all, the researchers found that the concentrations in the surrounding areas fell when they put a surgical mask on the source to cover the mouth and nose.
The highest exposure with a value of 0.44 was now on the passenger directly behind the infected person, on the next seat the value fell from 0.96 to 0.41.
But is that enough to prevent infection?
Even after reading the study, you don't know.
Larger particles: test with mask missing
In the second test setup with the larger particles, the riskiest place was the one opposite the source, where 0.2 percent of the particles arrived.
This is where the methodological weaknesses begin at the latest: The test was not carried out again with a mouth and nose cover, which is why, strictly speaking, not even the statement that the mask works in any case is not covered, the authors of the study only proved this for finer aerosols.
When asked, DLR announced that the device that generates the particles could not yet be equipped with a mouth and nose cover, but plans to make up for such measurements.
But experts also criticize the experimental setup as a whole.
Because only 6563 particles were emitted per minute.
"In reality, there are several hundred thousand or even millions," says Jürgen Blattner.
The managing director of BSR Messtechnik is one of the leading experts for particle measurement technology and aerosols in Germany.
He looked at the study by DLR and Bahn for WELT and thinks it is not very informative.
"I would not have published this study like this because I don't understand what it is supposed to say," says Blattner.
"You could have understood all of this with common sense."
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The expert cannot understand the section of the investigation into air conditioning technology either.
Here, the researchers tested whether the aerosol load can be reduced by using different filters.
So-called Hepa filters are used in air traffic, which can also separate particles the size of virus-contaminated aerosols.
But it was precisely these filters that the DLR researchers did not take into account in their studies; instead, the so-called G4 filters that are currently used in ICEs were only compared with so-called M5 filters.
However, according to Blattner, both models are not at all suitable for filtering out fine aerosols.
“G4s are coarse dust filters that you can use to filter pollen out of the air,” he says.
Study hides important things in the small print
Unsurprisingly, given the models chosen, the researchers came to the conclusion that the filters tested would not lead to any improvement.
For the railways, the matter is clear that expensive filters are not necessary: "The study shows that the indirect path of droplets and aerosols to the passenger through the air conditioning system in a rail vehicle does not really play a role," said the company.
"From the results there is no need to implement measures with regard to the air conditioning."
The researchers also simulated on the computer how particles spread in numerous different situations in the car.
But in the so-called short version only two figures are presented here.
At first glance, the result seems impressive: While the particles spread widely in the cabin without a mouth and nose covering, with a face mask they appear to remain above the infected person.
Only in the small print can it be seen that the situations are completely different: In the illustration without mouth and nose covering, the infected person coughed, in the illustration with mouth and nose covering, however, only breathed normally.
This gives the impression of a greater effect at first glance.
On request, DLR announced that not all simulations were carried out for “time constraints” and that a selection was made.
The short version "does not claim to be a complete scientific publication."
In general, it is noticeable that scientific standards such as literature references or measurement data series are completely missing in the short version.
When asked, DLR announced that a further publication in a scientific journal is planned, for which a so-called peer review will be carried out, i.e. other scientists will examine the results.
When and in which magazine it should be published has not yet been determined.
It will then also be interesting to see how the independent research colleagues rate the influence of Deutsche Bahn on the study.
It is true that both DB and DLR attach importance to the fact that this was not contract research, but a cooperation.
However, the railway was allowed to have a say in the test setup, the creation of the now published short version and the publication date.
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As early as September, Deutsche Bahn had caught the eye with a very far-reaching interpretation of another study on corona security in trains: The investigation had shown that train attendants were not infected with the virus more often than other people.
From this, the group derived that the overall risk on trains is not increased - even for passengers.
The fact that train attendants are constantly moving through the wagons and not sitting next to the same person for hours was not taken into account.
When it comes to interpreting the DLR study, the train goes very far: “The study shows that on the train, as in the rest of public life, the following applies: keeping your distance and wearing a face-to-face cover are the most effective ways of getting and to protect others from the corona virus.
Traveling by train is safe, ”said the company.
At least aerosol expert Blattner sees it a little differently: "I advised my people not to travel by bus and train during the pandemic."