Road Debris Causes Another Tesla Model S Battery Fire

In an incident that may turn out to be eerily similar to one that occurred a month ago, another Tesla Model S electric car caught fire last week after the driver struck a metal object on a Tennessee roadway.

”From what we understand, the driver ran over a trailer hitch, like a receiver hitch ball,” Larry Farley, Rutherford County Tennessee fire chief, told Design News. “When we got to the scene, there was heavy fire involvement.”

The accident, which occurred on Interstate 24 near Smyrna, Tenn., did not involve any injuries. It did, however, cause the vehicle's front end to be engulfed in flames. Photos on the Tesla Motors Club website showed the car’s body to be charred. ”It got so hot, the front of the car pretty much sank right into the asphalt,” Farley told us. “We had to jack the vehicle up to get water up under there to flood it and put it out.”

Tesla Motors told Design News it is looking into the incident. “We have been in contact with the driver, who was not injured and believes the car saved his life,” the company said in a prepared statement. “Our team is in Tennessee to learn more about what happened in the accident.”

The fire is the third for a Model S in a little more than a month. The first occurred in Kent, Wash., in October after a Model S struck a curved piece of metal in the roadway. The second took place in Merida, Mexico, after a Model S crashed into a tree and a concrete wall.

After the first fire, the National Highway Traffic Safety Administration issued a statement saying, “After reviewing all available data, NHTSA has not found evidence at this time that would indicate the recent battery fire involving a Tesla Model S was the result of a vehicle safety defect or non-compliance with federal safety standards.”

In his blog last month, Tesla CEO Elon Musk sought to quell concerns by writing that the Washington incident happened after the debris punched upward and impaled the car “with a peak force on the order of 25 tons.” Experts interviewed by Design News at the time described the incident as “bizarre,” and suggested there was little engineers could have done differently to prevent it.

Battery experts say lithium-ion packs can experience internal shorts and overheating after they are subjected to major mechanical deformation. “In a lithium-ion battery, you’ve got electrodes that are tens of microns from one another,” Elton Cairns, a professor of chemical and biomolecular engineering at the University of California-Berkeley, told Design News in 2011. “If you deform the cell case and it causes the electrodes to touch one another, there’s an internal short circuit. That can cause the cell to rapidly discharge and, in doing so, heat up.”

Tesla’s lithium-ion battery packs might be candidates for such mechanical deformations because they sit underneath the vehicle’s body.

Experts contacted by Design News last week said that if the incident happened as the driver described it, then it could be a concern. “Two of the same thing in a short period of time is definitely a pattern,” Ralph Brodd, a well known lithium-ion battery expert and founder of the consultancy, Broddarp of Nevada, told us. “They’ve got to do something to fix it if it happens that often.”

Brodd suggested that the armor plate protecting the bottom side of the car might need to be strengthened. “Nothing is indestructible,” he said.

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