None of the cars caught fire, and their batteries remained fully intact, shielded by an airtight steel exoskeleton and two other layers of protection that surround the 660-pound packs.
“Considering how they were tossed around and crushed, we think that is a very good indication of the safety performance of that vehicle,” said Bob Yakushi, the director of product safety for Nissan North America.
Nissan’s decision to encase the Leaf’s battery in steel may help explain why federal safety regulators investigating postcrash fire risks in the Chevrolet Volt do not have the same concerns about the Leaf. General Motors packages the Volt’s battery cells on a T-shaped steel tray with a plastic cover.
The durability and design of the Volt’s battery have come into question since two of them caught fire after being damaged in testing by the National Highway Traffic Safety Administration. The fires prompted the agency to open a formal defect investigation of the Volt, a low-volume but high-visibility model that G.M. has held up as proof it can lead the industry in advanced technology.
The N.H.T.S.A. examined the Leaf and other electric vehicles after the initial Volt fire but last month said its testing “has not raised safety concerns about vehicles other than the Chevy Volt.”
A General Motors spokesman, Robert D. Peterson, said the Volt’s battery was “fully encased by the steel floor pan or rails” and that the company chose to use material for the cover that did not conduct electricity. But the Ford Motor Company is following Nissan in putting a steel case around the pair of batteries that power an electric version of its Focus compact car, which it started building this month. The decision about the battery casing was made long before the Volt’s problems were known.
Although the N.H.T.S.A. has not yet crash-tested the electric Focus, Ford executives say internal testing has resulted in no damage to the actual battery cells. “Given that this is new technology, we chose to put that extra level of protection in,” said Derrick Kuzak, Ford’s group vice president for global product development.
Clarence Ditlow, executive director of the Center for Auto Safety, said he expected G.M. to recall the Volt to protect its battery more as Nissan and Ford do. Because G.M. has sold only about 6,000 Volts, doing so would cost a fraction of a typical recall, he said, but the bigger problem is repairing the damage to its image.
“Whenever you come out with an alternative vehicle, there will be problems with it,” Mr. Ditlow said. “But when you have a significant portion of the company’s success in the future based on a particular technology, you want to make sure you get it right, and they didn’t. Nissan clearly was ahead of G.M. in this.”
Mary Barra, G.M.’s senior vice president for global product development, said the company was studying whether it needed to make the Volt’s battery “more robust,” but she insisted that the car, which went on sale a year ago, was “fully developed” and not rushed into dealerships prematurely.
“If we have to do something, we will,” Ms. Barra said this month. “The one thing you don’t want to do is jump to conclusions.”
The Volt has been widely praised by reviewers and owners, but even a small flaw threatens to give the company a black eye. The Web site of the conservative radio talk radio host Rush Limbaugh depicts a crumpled Volt engulfed in flames, and a Republican congressman, Jim Jordan of Ohio, has called for a subcommittee hearing about the battery problems in January.
G.M. has defended the car, pointing out that no real accidents have resulted in a fire, but it has offered to lend a replacement vehicle to any Volt owners concerned about their safety. About 33 people have taken the company up on its offer, and G.M. has been working to satisfy a smaller number of owners who have asked to sell their Volt back.
In early June, a Volt caught fire three weeks after it was heavily damaged in a government crash test. The N.H.T.S.A. said the test, which simulates the car rolling over after striking a pole on one side, damaged the Volt’s battery and ruptured part of the liquid-cooling system that regulates the battery’s temperature.
The federal agency intentionally damaged three additional Volt batteries, one of which caught fire a week later. A second one emitted smoke and a brief spark.
G.M. officials have said they believe that the rotation allowed coolant to leak and later crystallize, possibly creating a short circuit. The N.H.T.S.A. did not disconnect the battery before storing the car, as G.M. has been training emergency personnel to do, because G.M. did not finish developing its postcrash protocol until July, after the fire occurred.
Any time a Volt is in a crash that deploys its air bags, G.M. learns of the incident through the car’s OnStar communication system. If the incident is deemed severe, G.M. sends engineers to examine the battery and drain it. Nissan says it does not need to respond to crashes in person but recommends that a damaged Leaf be taken to a Nissan dealership for repairs.
The Leaf also differs from the Volt in that its battery does not have a liquid-cooling system. Mr. Yakushi said laminated circuitry reduced the amount of heat produced.
The electric Focus and Tesla Roadster, a battery-powered car sold by California-based Tesla Motors since 2008, do have liquid-cooling systems. Tesla says it encloses each battery pack’s 6,831 cells in steel to protect them and dissipate heat.
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