The National Highway Traffic Safety Administration said Thursday there's no indication at this time that the fire was caused by a safety defect or that there was any violation of federal vehicle safety standards.
The agency said in a statement that it reviewed all available data and will continue to check consumer complaints and other information. A NHTSA spokesman said that he could not comment beyond the statement.
The Tesla Model S hit road debris on a freeway in Kent, Wash. The debris punctured an underbody shield and the battery, which is mounted beneath the passenger compartment. The crash touched off a fire that engulfed the front of the car. The driver escaped without injury and firefighters put out the flames.
Experts say when a battery cell is pierced, it can cause a short circuit that can lead to arcing and sparks that can touch off a fire.
The fire happened during the 16-day partial government shutdown earlier this month, delaying NHTSA's response. Normally the agency would send investigative teams to such an event shortly after it happens.
The fire became an Internet sensation when witnesses posted a video of it. The stock of Tesla Motors Inc., which is based in Palo Alto, Calif., tumbled as word of the fire spread.
Tesla CEO Elon Musk said the car, which starts at $70,000, apparently was impaled by a metal object. Musk, in a blog post, defended the car's battery technology and said fires are more common in conventional gas-powered vehicles.
The CEO said a curved metal object on the road was apparently to blame. The large object's shape led to a powerful hit on the underside of the vehicle, punching a 3-inch hole through an armour plate that protects the battery.
The car properly contained the blaze in one section of the battery, the company said.
Of the estimated 194,000 vehicle fires in the U.S. each year, the vast majority are in cars and trucks with gasoline or diesel engines. Electric vehicles make up less than 1 per cent of the cars sold in the U.S.
Tesla said the incident is the only fire ever to happen in one of its batteries. Although a Chevrolet Volt made by General Motors caught fire two years ago after a government crash test, neither GM nor Nissan, which make the top-selling electric cars in the nation, know of any real-world blazes in their vehicles. The government opened an investigation into the Volt fire, but closed it after GM agreed to a safety campaign to bolster shielding around the battery.
Tesla Motors' stock was up $4.10, or more than 2 per cent, to $177.25 in aftermarket trading on Thursday.Suggest a correction