Although employers must allow employees to work from home, many Berliners still rely on public transportation. A joint study by the Technical University of Berlin (TU) and the Charité Hospital has now tried to clarify how risky it is to use it. It was conducted on behalf of BVG.

Researchers from the TU's Experimental Fluid Mechanics department and the Charité's Laboratory of Biofluid Mechanics studied the dispersion of aerosols in various means of transportation in Berlin. According to their results, the aerosol concentration in BVG vehicles is reduced by 80 percent compared to a ventilated reference room.

In their experiments, the researchers used artificial theater fog for aerosol measurements. In this way, "virus-laden breathing air" was simulated, which human-like mannequins "inhaled." The positive influence of medical masks was not considered in the setup.

In particular, vehicle ventilation and the "targeted opening of windows and doors" helped reduce viral loads, the BVG statement said. Although this is not always possible, especially in older subways, overall 90 percent of the vehicles would open the doors automatically. In addition, the subways would have a ventilation system. This is an advantage in the current situation, as air is constantly blowing into the subway from outside.

Reference space is crucial for results
In fact, the reference space is crucial in determining how high or low the aerosol concentration in public transport is in comparison.

In response to a question from the Tagesspiegel, Christian Oliver Paschereit, head of the Department of Experimental Fluid Mechanics at the Technical University of Berlin, and Ulrich Kertzscher, head of the Laboratory for Biofluid Mechanics at the Charité, explained that the risk of infection can currently only be "represented relative to reference situations" because it is not known from virological research how many viruses lead to disease.

According to the researchers, the measurements show a comparison to a "ventilated reference room," where the risk is low, according to the RKI. The press release cites a medium-sized conference room as an example of such a reference room, as it would roughly correspond to the volume of a bus.

Level of infection risk depends on other factors
However, the risk also depends on other factors. For example, the researchers refer to an average travel time in the Berlin subway of ten minutes. However, if a sick person and other passengers spend a longer time together, the risk of infection also increases, the two researchers told the Tagesspiegel. So, for example, if you commute on the U5 for half an hour from Hellersdorf to Alexanderplatz, the risk of infection is higher.

The distance to other passengers also plays a role. The release says that due to the lower demand with full service, there is particularly much space in the vehicles. In the study, distances of half a meter to three meters were examined, the researchers stated to the Tagesspiegel. With increasing proximity, the aerosol concentration and the risk of infection would also increase.

Overall, only about 50 percent of passengers are currently on the road compared to before the pandemic, BVG said when asked. Although there are sometimes more and sometimes fewer passengers depending on the time of day, classic peak times can no longer be identified due to the low number of passengers.

Starting May 3, passengers a will be allowed to board buses at the front, BVG announced Monday. The driver's cabs are now equipped with dividers.

Photo by Keena Ventus