As of: 10/21/2021 9:47 a.m.
After a fire in a Stuttgart bus depot, individual transport companies temporarily shut down their e-buses. According to the police, a charging process could have caused the fire. How mature is the technology?
Many people in Stuttgart will not soon forget the evening of September 30th: A huge column of smoke rises above the city on the Neckar. The bus depot in the Gaisburg district is on fire, 25 buses are destroyed. Small explosions of bursting tires cause the residents to startle again and again. The more than 200 firefighters fight for two hours before they can get the fire under control.
Fear of further fires
Even around three weeks later, the traces of the fire are still clearly visible. The bus skeletons are unchanged in their place in the bus depot. Since the roof of the hall is in danger of collapsing, the fire investigations and clean-up work are delayed.
It is now clear: Two of the 25 destroyed buses in Stuttgart were on the road with a fully electric drive. According to the investigators’ first findings, charging an electric bus could have triggered the fire. To SWR-Information could be an e-Citaro from Mercedes-Benz with a new type of solid-state battery. In March, the manufacturer recalled buses of the same type due to insulation faults. The question that is in the room: How secure is the technology? Are further fires looming?
Battery technology is considered safe
Maximilian Fichtner is a battery expert and managing director of the Helmholtz Institute in Ulm. If you talk to him about the use of batteries in vehicles, it quickly becomes clear that Fichtner trusts the technology and gives the all-clear after the fire in Stuttgart. A fire can never be completely ruled out, according to Fichtner, “but from the statistical point of view, battery-powered vehicles burn twenty times less often than combustion engines.” An assessment that the General Association of the German Insurance Industry GDV shares: “In our assessment, electric cars do not pose a higher fire risk than vehicles with internal combustion engines.”
The Fichtner expert even rates the solid-state battery as installed in the e-Citaro from Mercedes-Benz as particularly safe. This type of battery has already collected 20 million fleet kilometers in the “Blue Cars”, an electric car from France. “The batteries are very safe. By the way, very similar batteries are used in the iPhones.”
Charging error as the cause?
In the classic battery, a liquid separates the storage material in the plus and minus poles. “In the classic battery, this electrolyte consists of an organic liquid,” says Fichtner. This liquid could also burn. “Those are the battery fires that we know. That can hardly happen with solid-state batteries. There is no liquid here, but a plastic film between the plus and minus poles. And that is per se safer.”
If the fire in Stuttgart was actually triggered by the Mercedes e-Citaro, Fichtner assumes a charging error: “If you overcharge the battery, for example, it can theoretically lead to a critical condition and a fire.”
Fires also in Hanover and Düsseldorf
The fire in the bus depot in Stuttgart is the third major fire at a transport company in 2021. In June, a fire at the ÜSTRA depot in Hanover destroyed eight buses, including five electric buses. The Rheinbahn lost 38 buses in Düsseldorf in April as a result of a major fire. E-buses were also affected here. A report by the Düsseldorf public prosecutor comes to the conclusion that “the fire had a technical cause”. Exactly which one remains unclear. The investigation continues in Hanover. When asked, it was said, “But they are so advanced that we can rule out a special or increased fire risk due to the type of drive and charging technology of the e-buses”.
A burnt out bus in the depot in Stuttgart. A total of 25 buses were destroyed.
Image: SWR
The fires are unsettling the industry. And come – in the middle of the transformation from diesel to electric bus – at an inopportune time. After the fire in Stuttgart, transport companies in Germany reacted very differently. While the Wiesbadener Verkehrsbetriebe want to continue using their 40 e-Citaros with solid-state batteries, the Münchner Verkehrsgesellschaft decommissioned eight electric buses of the same type in October. “Safety is always our top priority,” says MVG Managing Director Ingo Wortmann. “We have therefore decided to take the vehicles out of operation as a precaution until detailed information about the fire in Stuttgart is available.”
More buses, too few depots
The responsible industry association, the Association of German Transport Companies (VDV), has a completely different explanation for the three major fires this year. “We have no accumulation of damage from electromobility,” says VDV’s technical director, Martin Schmitz. “We have kept increasing the number of bus depots in recent years. There has been a strong increase in demand, more buses, but not necessarily more depots. If vehicles are less than a meter apart, there is a high risk that other vehicles will come with them start to burn, “says Schmitz. You need more space again.
In order to prevent further large fires, more decentralized depots could help, and one also has to think about fire protection walls and smaller fire compartments in the future. But it is clear, according to Schmitz: “E-buses are not extremely dangerous.” There is a certain risk of fire regardless of the drive, and this ultimately also affects diesel buses.
In Stuttgart, the police continue to focus their investigations on the battery of the electric bus. “Comparative measurements are planned for buses of the same construction,” says police spokeswoman Ilona Bonn on request. For example, it is about the development of heat and the question of whether voltage is generated when the battery is not connected. At the request of the SWR the Daimler Group emphasizes that the cause of the fire has not yet been determined. EvoBus, the manufacturer of the Mercedes-Benz e-Citaro, supported the investigation and was very interested in the investigation.