They indulge in a strange game of tennis. After the spectacular fires of two electric buses in the heart of Paris in April, the manufacturer, Bolloré, and the operator, the RATP, passed the buck. Not yet on the possible responsibilities of one or the other, but on the progress of the investigation. For the first accident which occurred on April 4 on boulevard Saint-Germain in the 5th arrondissement, the investigations carried out by the company Bluebus are very advanced. “We determined the cause of the fire and applied a “corrective” in the days that followed on all the buses in the series (Bluebus 5SE), explains one of the spokespersons for the group subsidiary. Bolloré. It is not up to us to give details but to the owner of the devices.” For his part, the latter makes a comeback from the baseline in the opposing camp: “The maintenance of the batteries is not the responsibility of the RATP which remain guaranteed until half-life (7.5 years). It is to them that you have to turn if you want to know what this corrective consists of”, assures an official of the autonomous transport authority. For the record, this fire is not minor: if it caused no injuries, it led to the total destruction of the vehicle.
An electronic problem at the origin of the first fire
Very quickly, some specialists wondered about the composition of the batteries which could be the source of overheating: in the most common technology, that of lithium-ion batteries with liquid electrolyte, this phenomenon can occur with the creation dendrites, that is to say lithium metal filaments which can pass through the porous separator separating the anode from the cathode. In these rare cases, a short circuit is created which can cause sparks in the heart of a cell. Another known cause is linked to the presence of the elements Cobalt and Nickel at the positive electrode, the properties of which can cause “thermal runaway”. “These two scenarios are very unlikely with the batteries developed by Bolloré because these cells do not use liquid electrolytes and neither nickel nor cobalt, specifies Patrice Simon, Deputy Director of the Network on Electrochemical Energy Storage (RS2E) at the University of Toulouse III – Paul Sabatier. On the contrary, the “all-solid” technology specific to the Breton company has moreover largely proven itself with years of operation in Autolib cars.” Thus, since the RATP has mentioned the implementation of a “corrective”, it could be that the problem is of electronic origin, that is to say a malfunction of the battery charge control software . A hypothesis confirmed half-word by the head of Bolloré whom we interviewed: “it is not our batteries that are the problem.”
Three investigations carried out
It was still necessary to wait for the second disaster, on April 20, not far from the François Mitterrand Library (XIIIth arrondissement) much more spectacular since the 12-meter vehicle with its batteries on the roof saw a column of flames rise towards the sky, with a release of smoke and many cinders – fortunately the driver had the reflex to evacuate the passengers immediately before taking shelter – so that the RATP finally decided to temporarily withdraw the 149 Bluebuses in operation . “But for the time being, we are not making any connection between the two incidents”, continues the RATP spokesperson, who insists on the fact that no less than three investigations have been carried out: one internally, one on the side of Bolloré and a final one by the Land Transport Accident Investigation Bureau (BEA-TT). Before putting these incidents into perspective: “Since the beginning of 2021, there have been 26 fires, including 4 on electric buses”. But the more time passes to carry out these assessments, the more suspicion grows around the electric strategy of the RATP, which today has nearly 500 vehicles of this type (purchased from the Bolloré subsidiary, but also from the Heuliez and Alstom) out of a total of 4,700 buses.
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A greening of the fleet which is not currently in question since the Régie has placed an order for 451 additional vehicles. But that worries the unions: the RATP carries out preventive maintenance, that is to say that its agents check approximately every six months, all the organs of the bus with the exception of the batteries according to the manufacturer’s procedures. The RATP bus “maintainers” therefore see it as a loss of prerogatives which does not play in favor of safety, especially since their workforce “has halved”, according to Cemil Kaygisiz, the general secretary of the CGT Bus RATP , quoted by our colleagues from Les Echos.
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The RATP must therefore act quickly and speed up the investigation procedures. She promises, finally, that the return to service will not take place before an additional independent investigation has been completed. Suffice to say that the Bluebus should remain in the garage for a long time.
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