Tesla fire originated in battery pack

Officials are saying a fire that destroyed a Tesla electric car near Seattle earlier this week began, unsurprisingly, in the battery pack. The driver, according to the AP, said he believed he had struck metallic debris on the highway. The incident could reignite concerns about the safety of Li-ion batteries. Tesla shares fell $12.05 to $180.95 Wednesday.

Will Oremus in Slate says that NHTSA would normally investigate such an incident but cannot do so because NHTSA’s field investigations have been suspended because of the government shutdown.

Update: Elon Musk now has a blog post up regarding the incident. He writes, “…a Model S traveling at highway speed struck a large metal object, causing significant damage to the vehicle. A curved section that fell off a semi-trailer was recovered from the roadway near where the accident occurred and, according to the road crew that was on the scene, appears to be the culprit. The geometry of the object caused a powerful lever action as it went under the car, punching upward and impaling the Model S with a peak force on the order of 25 tons. Only a force of this magnitude would be strong enough to punch a 3 inch diameter hole through the quarter inch armor plate protecting the base of the vehicle.”

Musk notes that the driver was able to stop the car and exit the vehicle safely. He said that the fire was contained by internal firewalls within the battery pack.

He adds, “Had a conventional gasoline car encountered the same object on the highway, the result could have been far worse. A typical gasoline car only has a thin metal sheet protecting the underbody, leaving it vulnerable to destruction of the fuel supply lines or fuel tank, which causes a pool of gasoline to form and often burn the entire car to the ground. In contrast, the combustion energy of our battery pack is only about 10% of the energy contained in a gasoline tank and is divided into 16 modules with firewalls in between. As a consequence, the effective combustion potential is only about 1% that of the fuel in a comparable gasoline sedan.”

He cites National Fire Protection Association figures indicating, for conventional automobiles, one vehicle fire for every 20 million miles driven, vs. one fire in 100 million miles for Tesla. He concludes, “…there should be absolutely zero doubt that it is safer to power a car with a battery than a large tank of highly flammable liquid.”

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