BVG commissions TU Berlin and Charité to quantitatively examine aerosol dispersion in local public transport vehicles
Traveling by public transport in Berlin during the coronavirus pandemic remains safe for both passengers and staff. This is the conclusion of a recent study conducted by the Chair of Fluid Mechanics at Technische Universität Berlin and the Experimental Fluid Mechanics Lab at Charité – Universitätsmedizin Berlin. A team of researchers led by Professor Dr.-Ing. Christian Oliver Paschereit and Dr.-Ing. Ulrich Kertzscher conducted tests for the BVG (Berlin’s public transport authority) to determine the dispersion of aerosols in metro trains, trams and buses.
The tests were conducted using artificial theater fog and aerosol measurements of simulated respiratory air containing viruses breathed in by test dummies. The researchers were able to determine that ventilating vehicles and opening windows and doors results in an effective reduction in the concentration of aerosols of up to 80 percent. The research does not take account of the beneficial effects of the medical masks currently worn by passengers.
The volume of a bus is about the same as that of a medium-sized conference room. Opening the doors at every stop has roughly the same effect as opening the windows every 90 seconds during a meeting. It also needs to be remembered that passengers are often only on board for a few minutes at a time.
Professor Dr.-Ing. Christian Oliver Paschereit, head of the Chair of Fluid Mechanics at TU Berlin: “We are delighted that we have been able to use our new measurement technology to contribute to an assessment of aerosol dispersion in public transport and the risk of infection with SARS-CoV-2. We have been able to demonstrate that the use of ventilating systems and opening windows and doors results in a substantial reduction in the concentration of aerosols in the public transport vehicles we examined.”
Dr.-Ing. Ulrich Kertzscher, head of the Experimental Fluid Mechanics Lab at Charité: “Using our measurement system in various types of vehicles during operation was an exciting challenge. We are both surprised and delighted that the results have proven so positive. As we expected, measures are required, but opening windows and doors in combination with ventilating systems significantly reduces the build-up of aerosols in buses and trains.
Eva Kreienkamp, chair of the board of the Berlin Transport Authority (BVG) “I am delighted that this study has now confirmed that the use of buses and trains does not present an increased risk of infection for passengers or staff. Wearing a mask and keeping distance in combination with good ventilation means we can continue to travel together in safety.”
Dr. Manuela Huetten, senior company doctor and pandemic officer at the BVG: “It was particularly important for us that the study examined the effectiveness of protective screens on our buses. Unlike in metro trains and trams, our bus drivers do not work in a separate enclosed space. The study shows that our new protective screens are an effective means to reduce the spread of aerosols from passenger areas to driver areas and thus provide good protection. Used in combination with effective ventilation of the driver space, the screens provide a high level of safety in the work place.
Despite the fact that current demand is only 45 percent of that during the period prior to the coronavirus, the BVG continues to operate a full schedule of buses and trains and has actually increased its offers for school children as well as the number of vehicles on selected bus routes. This has resulted in less crowded vehicles. Wherever technically possible, the doors on trains and buses open automatically at every stop and station. The findings of the study are now being used to implement a more effective use of ventilation and the opening of windows on public transport vehicles to further reduce the concentration of aerosols.
The use of medical masks and regular air exchange provide protection for passengers in buses and trains. In April 2020, Berlin became the first German state to introduce mandatory wearing of masks in public transport as a measure to contain the pandemic. As of January 2021, passengers are required to wear a medical mask, such as a surgical mask or masks with FFP2 or KN95 standard.
In July 2020, the BVG became the first local transport authority in Germany to introduce its own fine of 50 euros for unauthorized non-use of masks. This fine is independent of official fines. For a number of months now, Berliners have demonstrated a reassuringly high level of mask usage of approximately 97 to 99 percent.