A defect in the manufacturing of the batteries, leading to a short circuit, is responsible for two fires in electric buses manufactured by the Bolloré group and operated by the RATP in April 2022, according to the investigation report published Wednesday October 30.
A Bluebus electric bus caught fire in the 13e district of the capital on April 29, 2022, a few weeks after another bus fire, in the 5e borough. There were no injuries in these two incidents. After the second disaster, the RATP immediately withdrew from circulation, “as a precautionary measure”the 149 electric buses in the series produced by Blue Solutions, a Bolloré group company.
“The most probable direct cause” fires is « un court-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, themselves made up of a “stacking” of twenty cells, isolated from each other by sheets of insulation. “Some leaves” have been “poorly positioned” in the factory and did not allow sufficient insulation between the cells – a defect which was not detected by quality control, explains the report, which highlights that the manufacturer had launched the recall of the buses concerned 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 for electric vehicles. They suffered a “thermal runaway”that is to say an uncontrolled reaction until conflagration.
The investigation report also points out “a delay in defining the technical regulations applied” to vehicles with innovative technologies. In this case, the approval does not require any driver warning device in the event of thermal failure of the batteries. And certain approval tests planned for conventional lithium-ion batteries, “in particular fire resistance tests”do 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” pour “guarantee” safe evacuation of passengers.
Read also | Article reserved for our subscribers In big cities, buses slow down
Read later
