Tesla to NHTSA: Investigate Our Model S Fires

Charles Murray

November 19, 2013

4 Min Read
Tesla to NHTSA: Investigate Our Model S Fires

The National Highway Traffic Safety Administration (NHTSA) said today it is opening an investigation to examine the potential risks associated with "undercarriage strikes" on Tesla's Model S electric cars.

In a web posting, NHTSA's Office of Defects Investigation (ODI) said it is opening the investigation in response to two incidents -- one in Washington and another in Tennessee -- in which vehicles struck metallic objects that led to thermal runaway. The posting described the problem as "Deformation/intrusion into the propulsion battery."

NHTSA's announcement came just hours after a blog post by Tesla CEO Elon Musk saying that the company is making changes in response to the recent fires. He said the company will make an "over-the-air" software update to Model S air suspension systems to provide higher ground clearance at highways speeds. The company will also amend its warranty policy to cover damage due to a fire, even in cases of driver error. Finally, Musk said Tesla had requested that NHTSA undertake a full investigation into the fires.

Given that the incidence of fires in the Model S is far lower than combustion cars and that there have been no resulting injuries, this did not at first seem like a good use of NHTSA's time compared to the hundreds of gasoline fire deaths per year that warrant their attention. However, there is a larger issue at stake: If a false perception about the safety of electric vehicles is allowed to linger, it will delay the advent of sustainable transport and increase the risk of global climate change, with potentially disastrous consequences worldwide. That cannot be allowed to happen.

A statement from NHTSA, however, offers a different view of the events. "NHTSA's decision to open any formal investigation is an independent process," the statement read. "In regards to Tesla, the agency notified the automaker of its plans to open a formal investigation and requested their cooperation, which is standard agency practice for all investigations. The automaker agreed to do so."

In his posting, Musk again made a case for the safety of electric vehicles, emphasizing the fact that gasoline-powered cars are far more dangerous:

There is a real, physical reason for this: a gasoline tank has 10 times more combustion energy than our battery pack. Moreover, the Model S battery pack also has internal firewalls between the 16 modules and a firewall between the battery pack and passenger compartment.

He added that the firewalls made it possible for the driver in the Tennessee fire to retrieve pens and papers from the glove compartment before exiting the vehicle.

The two recent Model S incidents that occurred in the US involved vehicles striking metallic objects. The first, near Seattle, happened after a driver rolled over a curved piece of metal. The second, in Tennessee, occurred after a Tesla owner hit a trailer hitch on an Interstate highway.

After the accidents, experts told Design News that there were two possible failure mechanisms. The metallic objects could have deformed the battery casing, causing short-circuiting and thermal runaway. Or the metal could have punctured the batteries, causing spillage of electrolyte, which might have been ignited by nearby sparks.

Although the recently announced fixes may improve the safety of the lithium-ion packs, experts have said that the designers couldn't be faulted in those incidents. "There's no such thing as absolute perfection," David Cole, chairman emeritus of The Center for Automotive Research, told us after the October fire. "As a designer, you just hope you can get fairly close to it."

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About the Author(s)

Charles Murray

Charles Murray is a former Design News editor and author of the book, Long Hard Road: The Lithium-Ion Battery and the Electric Car, published by Purdue University Press. He previously served as a DN editor from 1987 to 2000, then returned to the magazine as a senior editor in 2005. A former editor with Semiconductor International and later with EE Times, he has followed the auto industry’s adoption of electric vehicle technology since 1988 and has written extensively about embedded processing and medical electronics. He was a winner of the Jesse H. Neal Award for his story, “The Making of a Medical Miracle,” about implantable defibrillators. He is also the author of the book, The Supermen: The Story of Seymour Cray and the Technical Wizards Behind the Supercomputer, published by John Wiley & Sons in 1997. Murray’s electronics coverage has frequently appeared in the Chicago Tribune and in Popular Science. He holds a BS in engineering from the University of Illinois at Chicago.

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