A defect in the manufacturing of the batteries, which caused a short circuit, is responsible for two fires in electric buses manufactured by the Bolloré group and exploited by the RATP in April 2022, according to the investigation report published on Wednesday, October 30.
A Bluebus electric bus caught fire on the 13thmy district of the capital on April 29, 2022, a few weeks after another bus fire, in 5my city. There were no injuries in these two incidents. After the second disaster, the RATP was immediately withdrawn from circulation, “as a precautionary measure”the 149 electric buses of the series produced by Blue Solutions, a Bolloré group company.
“The most probable direct cause” the fires are “a short circuit” at the cell level, inside the batteries. “The investigations carried out showed that this cause lay in the battery manufacturing process”concludes the Land Transport Accident Investigation Office (BEA-TT).
Each bus is powered by six battery packs, each containing nine modules, in turn composed of a “stacking” of twenty cells, isolated from each other by insulation sheets. “Some leaves” has been “poorly positioned” in the factory and did not allow sufficient insulation between the cells, a defect that was not detected by quality control, explains the report, which highlights that the manufacturer had launched the withdrawal of the buses in question in 2022.
“thermal runaway”
The batteries used in these buses are solid-state lithium metal polymer (LMP) batteries, which compete with the lithium-ion batteries most commonly used in electric vehicles. They suffered a “thermal runaway”that is, an uncontrolled reaction until conflagration.
The investigation report also notes “a delay in the definition of the applied technical regulations” to vehicles with innovative technologies. In this case, the approval does not require any device to warn the driver in the event of thermal failure of the batteries. And certain approval tests planned for conventional lithium-ion batteries, “in particular, fire resistance tests”does not apply for LMP technology.
The report also recommends, for example, “provide the roof” electric buses, whose batteries are installed in the roof structure, a “thermal protection” For “guarantee” safe evacuation of passengers.
