MILAN (AP) — Italy's transport minister is questioning the spread of electric vehicle technology following the fiery crash of a fully electric shuttle bus that killed 21 people in mainland Venice. But the battery chemistry used by the Chinese bus maker makes it less prone to catastrophic fires, experts said.
Transport Minister Matteo Salvini said the accident involving an electric bus that drove through an overpass guardrail during rush-hour Tuesday should be "cause for reflection."
"It is early to comment,'' Salvini said, "But someone told me that electric batteries catch fire more quickly than other power sources. In a moment in when everything must be electric, there is cause for reflection."
Prosecutors have ordered an expert examination of the guardrail as one of several strands of the investigation, which is looking at such possible causes as a sudden illness to the driver, who was among the dead, or a risky road maneuver.
The city-owned, fully electric bus was traveling on a central raised thoroughfare when it drove against the guardrail for some 50 meters (yards) before breaking through both the guardrail and a rusted handrail and plunging 10 meters. It landed upside down, its front completely crushed. When rescuers arrived it was on fire, and some survivors, including a young Ukrainian girl, were being treated for severe burns.
Chief Prosecutor Bruno Cherchi said Thursday there was no evidence the fire started before the bus hit the ground.
The bus maker, Yutong Group of China, uses lithium-iron-phosphate batteries in nearly all its models. Experts say that mix is generally less prone to extra-hot, fast-spreading blazes than other chemistries, including nickel-manganese-cobalt oxides, which is used in many electric passenger cars.
"They're generally safer for fire safety," said Adam Barowy, an engineer at the Fire Safety Research Institute, the nonprofit arm of Underwriters Laboratories based in Columbia, Maryland. "There's not as much energy released from a cell of an LFP chemistry as pretty much any of the other chemistries."
On its English-language website, Yutong lists lithium-iron-phosphate as the chemistry on every model for which a battery type is shown. It's not clear which model was involved in the crash, and Yutong didn't respond to messages from The Associated Press.
Experts say that since lithium-iron-phosphate doesn't store as much energy as other chemistries, it has less traveling range. But it's also less prone to what experts call "thermal runaway," when one battery cell overheats and causes chemical reactions and fires in the others.
In batteries that use nickel or cobalt, oxygen can be released if the temperature gets too hot, fueling a fire. But in a lithium-iron-phosphate battery, there is a strong bond between oxygen and phosphorus, keeping the oxygen in place, said Reeja Jayan, an associate professor of mechanical engineering at Carnegie Mellon University in Pittsburgh.
Fires can still happen in lithium-iron-phosphate batteries in a crash if a cell is somehow breached and short circuits, raising the temperature. That would cause a chemical reaction that could ignite liquid electrolytes or lithium, Jayan said.
But without oxygen, the fire would less intense than batteries that have nickel, manganese or cadmium, she said.
"In many cases, for instance when the battery is operating normally, you can keep that oxygen within the structure," Jayan said. "But if you have a fire, none of that works."
Battery researchers are working on getting more range out of lithium-iron-phosphate batteries, Jayan said, and they are also figuring out how to make nickel-manganese-cadmium batteries safer.
"To get (high energy storage) capacities, you still have to make a deal with the Devil," using unstable chemistries, she said. "But it's going to be figured out. I am positive of that."
Venice Mayor Luigi Brugnaro told AP that the accident did not provoke any rethink of the city's plan to expand its fleet of electric-powered buses. The bus that crashed was just one year old.
That the bus drove off an overpass "has nothing to do with the fact that it is electric," the mayor said.
Salvini, who heads the right-wing Lega party, was criticized for focusing on electric vehicle technology when one of the elements under investigation is the guardrail that gave way, which falls under his purview as infrastructure and transport minister.
"Speculating on the 21 deaths … to revive his battle against electric vehicles is indecent and cruel,'' said Democratic Party lawmaker Alessandro Zan.
Venice's infrastructure official, Renato Boraso, told SKY TG24 private television that the guardrail scraped by the bus had been recently changed as part of regular maintenance and that the overpass met all standards.
"I agree with the prosecutors, who said they need to understand why this bus, which scraped against against the guardrail for dozens of meters, ... never engaged the breaks and never steered away,'' Boraso said.
Nine Ukrainians were among the tourists killed, along with four Romanians, three Germans, two Portuguese, one Croat and one South African. All had been sightseeing in Venice and were traveling on the shuttle back to a campground on the Venetian mainland when the accident occurred.
Prosecutors are looking at video recorded both at the scene and inside the bus as well as the vehicle's data recording device. Authorities also plan to do an autopsy on the driver and examine his cellphone.
The 15 survivors, including four Ukrainians, two Spaniards and a French person, are all hospitalized with serious to critical injuries. Some are not yet able to speak, both for physical and psychological reasons, Cherchi, the chief prosecutor, said.
"Many of the injured have lost close relatives, and are in a very delicate psychological condition,'' he said.
One of the survivors is a 24-year-old Croatian man on his honeymoon whose wife, reportedly six-months pregnant, died in the crash, according to Croatian press reports.
The four Romanian victims were a family residing in Germany, including two girls, 8 and 14 years old, according to Romanian media channel Digi24.