Lithium battery experts say EV batteries are at least 20 times less likely to catch fire when used in road vehicles than diesel or gasoline vehicles.

Hitachi’s train uses Nissan Leaf cells, which have been involved in 16 fires in the 14 years they’ve been used in road vehicles, according to EV Fire Safe, which collects data on battery fires around the world. This consists of more than 500,000 cells sold worldwide.

“Lithium batteries are very safe when managed properly,” says Jon Simpson, a former firefighter turned fire safety consultant.

However, when lithium batteries fail, they can experience thermal runaway; This means the cell is exposed to uncontrollable temperature increases, making the fire difficult to control and extinguish.

Jon Hughes, managing director of Fire Training UK, says the kind of “catastrophic event” that could cause something like this would be a crash or derailment where a cell is damaged.

But consultant battery electrochemist Euan McTurk says Nissan Leaf cells are “a lot tougher than people realize.”

For them to catch fire, he says, “the actual cells have to be pierced in a spectacular way, which means passing through a very strong external structure.”

Part of Hitachi’s testing involved deliberately destabilizing the cell, including puncturing it and overheating it, says Chris Dautel, the manufacturer’s senior electrical engineer.

He adds that Hitachi has placed a heat shield around each cell to prevent the problem from spreading to other cells, meaning “there is no danger to passengers in the event of (a) thermal runaway.”

There is also a cooling unit on the roof of the train to regulate the temperature of the batteries, and the company has developed software that monitors and regulates the cells.

Fire safety consultant Mr Simpson says the immediate response to a lithium battery fire is to fill the cell with as much water as possible to cool it, but depending on where the fire occurs this may not be appropriate.

“Tunnels are probably the riskiest areas in the railway environment,” says electrical engineering consultant Graham Kenyon. “If there’s a fire, probably the worst thing you’re going to encounter when evacuating people is smoke, fumes, steam and toxic fumes.”

In some cases, it is safer for the fire crew to leave the battery to ignite on its own. But leaving a train on the track can cause major disruption.

Dautel says a wagon with a battery fire can be moved out of the way even while it’s burning, such is the effectiveness of the fire barrier around the cells.

“We would evacuate the passengers in case of an incident, but they wouldn’t see anything,” he says.

He adds that since each unit operates independently, the train can move on its own using batteries in other carriages or be pulled by another train.