The driver said the car hit a chunk of metal debris on the freeway, presumably at freeway speeds. He pulled off the road because of the incident. But then at the end of the exit ramp, his car caught fire and was eventually consumed in flames. Firefighters arrived and attempted to put out the fire, only to find that even though they thought it was extinguished, the car reignited.
Tesla has reacted to the accident, noting that the car had a "direct impact" with a "large metallic object," which hit "one of the 16 modules within the Model S battery pack." This impact seemingly pierced various physical protective layers around the lithium-chemistry cells inside the module, causing the battery to catch fire. Tesla stressed that the power pack for its car is designed to be resilient to this sort of failure, and to contain damage to as few modules as possible—that's why the fire was contained to what Tesla calls a "small section in the front of the vehicle." But a quick glance at the video of the event may cause you to question the use of the word "small."
What's happened here may remind you of the lithium cell fires that caused Boeing's Dreamliner aircraft so many expensive woes, and it may even remind you of the incident that largely ended Concorde's supersonic career—after it hit a large metallic object at high speed on a runway, piercing a fuel tank and leading to a fire. But don't be too quick to condemn Tesla or its technology. The use of large lithium cells in cars is very new. As more and more electric cars hit the streets there will, inevitably, be more headlines like this one—and the technology, just as it has done for a century of gasoline powered cars, will simply get safer with time.
Update: On Oct. 24, the National Highway Traffic Safety Administration said it will not investigate the Model S fire. The agency said in a statement: "After reviewing all available data, the National Highway Traffic Safety Administration hasn't 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 noncompliance with federal safety standards."