Tesla fires spark search for safety lessons

At Tesla Motors Inc. and beyond, a hunt for answers is on.

The three Tesla Model S electric sedans that have caught fire since Oct. 1 have drawn wide public scrutiny, pushing down Tesla's stock price and prompting angry rejoinders from CEO Elon Musk, who says the media have overlooked the hundreds of gasoline cars that catch fire in the United States every day.

But the fires have served as a clear reminder that vehicles running on lithium ion batteries -- although not filled with a combustible fuel -- have risks of their own. Executives and engineers across the industry say they are watching the episodes closely, hoping to glean lessons on protecting battery packs from harm.

Engineers have put forth a number of hypotheses: Is it Tesla's battery chemistry that's to blame? Is it the way Tesla packages its battery cells into battery packs? Or is it Tesla's idiosyncratic batteries-between-the-axles design?

Or is it just bad luck?

"The kind of thing happening to the Tesla is pretty bad," says Venkat Srinivasan, a lithium ion battery expert at Lawrence Berkeley National Laboratory in Berkeley, Calif. "Under those conditions, any battery would have problems. That's just the reality."

And yet, several years after automakers started selling battery-powered cars by the thousands, flaming EVs are relatively rare. Several large automakers that sell them, such as General Motors, Mitsubishi and Nissan, say none of their EVs have burned on the road.

"There have been no fires involving the Nissan Leaf, either through extensive and extreme testing or in the real world," a Nissan spokesman wrote in an e-mail to Automotive News.

U.S. auto safety regulators opened an investigation into the Chevrolet Volt in late 2012 when it caught fire days after a crash test; the investigation was closed a few months later, when they concluded there was no defect.

"Generally, all vehicles have some risk of fire in the event of a serious crash," the regulators said at the time.

Still, "this does not help any EV manufacturer," said a source at a competing automaker, who asked to not be named because he was not authorized to talk about Tesla. "Yes, we're paying attention. Yes, we're seeing what we can learn."

Tesla doesn't intend to call back the Model S sedans it has sold. There is "definitely not going to be a recall," Musk said at a conference last week.

It could be months before regulators decide whether to investigate the Tesla for possible defects. "We are still in a data collection mode," David Strickland, head of the National Highway Traffic Safety Administration, told reporters last week.

To open a formal investigation, NHTSA engineers would need to conclude that the Model S probably has a safety-related defect, which means gauging how often comparable cars catch fire and whether the circumstances that caused the fire are common.

Allan Kam, a former senior enforcement attorney at NHTSA, said he doubts the agency will start a formal investigation. Cars must be designed to handle normal driving conditions and mild abuse, he said, but not extreme abuse.

"It's a pretty unusual circumstance," Kam said of the Model S incidents, which involved the cars running over large pieces of debris. NHTSA "could argue the shield was inadequate compared to an industry norm, but I'd be reluctant to say it's a safety-related defect when the battery was damaged by metal debris. Normally, you wouldn't be driving over that."

Experts say the chemistry of the Model S battery is probably not an issue. And Tesla has made clear that it stands by its configuration. On Oct. 30, the automaker said it has expanded a 2011 contract and will now buy about 2 billion battery cells from supplier Panasonic Corp. over four years.

A top executive at a rival battery supplier agreed that the Panasonic batteries are not the problem but said there may be room to improve the quarter-inch-thick aluminum shield that protects the battery in the Model S.

"The more mature companies view the battery as the fuel tank and they know how to handle the fuel and build in the appropriate protection," the source said. "So it could be a design issue and a robustness issue."

Daniel Doughty, a private consultant from Albuquerque, N.M., who led an SAE study of battery safety, said Tesla's under-the-floor placement of the battery isn't flawed.

"I don't see any inherent problems with that," he said. "It seems to me to be a pretty well thought out, robust design."

Even if there are differences from EV to EV, the fact that gasoline is so flammable may also inoculate Tesla against recalls.

"There's a lot more energy in gasoline per pound or per liter than you'll ever get into any sort of battery," said Srinivasan, the battery researcher. "So if you ever want to see something bad, you can see something really bad with gasoline."