The blaze on Wednesday afternoon near Smyrna, Tenn., engulfed the front of the car. A spokeswoman for the Tennessee Highway Patrol says the Model S ran over a tow hitch, which hit the undercarriage of the car, causing an electrical fire.
It's the second Model S blaze involving road debris. In early October, a driver near Seattle hit debris that pierced a shield and the battery pack, causing a fire. In the other fire, a driver in Mexico crashed into a concrete wall and a tree at a high speed.
Shares of the carmaker, based in Palo Alto, Calif., fell 7.5 percent to $139.77 on Thursday. That's on top of Wednesday's plunge of 14.5 percent, after concerns about a battery shortage, as well as the costs Tesla will incur as it builds more cars, spooked some investors. The shares are still up 312 percent this year.
The Model S has as a large battery pack under the passenger compartment, protected by a quarter-inch-thick metal shield. Experts say that if debris punctures the shield and damages the battery, it can cause shorts and arcing that can touch off fires.
The National Highway Traffic Safety Administration, the U.S. government's auto safety watchdog, says the agency will contact Tennessee authorities to determine if there are safety problems that need further action. NHTSA decided last month not to investigate the Seattle-area fire, saying there was no evidence it was caused by a safety defect.
The driver in Tennessee was able to pull onto an emergency lane and escape. Tesla said it has sent a team to investigate.
Company spokeswoman Liz Jarvis-Shean says the fire was not spontaneous. She says Tesla contacted the driver, who believes the car saved his life. Tesla CEO Elon Musk has said that the design of the Model S is safer than that of a car with a conventional fuel tank.
The fire burned the front of the car, according to pictures posted on the Jalopnik.com and Valuewalk.com websites.
Larry Farley, Rutherford County fire chief, says the blaze was so hot and intense that it melted the front of the car. "It pretty much just melted to the road," Farley says.
The passenger compartment was in pretty good shape after the flames were extinguished, Farley says. A Fire Department report estimated the value of the loss from the fire at $120,000.
According to the U.S. Fire Administration, there are around 194,000 vehicle fires on U.S. roads each year. The vast majority — 61 percent — start in the engine area, while 15 percent start in the passenger area. Approximately 300 people die and 1,250 are injured in U.S. vehicle fires each year. Most happen in gas-powered cars, which make up the vast majority of cars on U.S. roads. Electric vehicles make up less than 1 percent of the cars sold in the U.S.
General Motors and Nissan make the top-selling electric cars in the nation, the Volt and Leaf. Neither knows of any real-world blazes in those vehicles. A Chevrolet Volt caught fire two years ago after a government crash test, but the government closed an investigation into the incident after GM agreed to a safety campaign to bolster shielding around the battery.
GM has sold more than 50,000 Volts in the U.S. since late 2010. Nissan has sold almost 38,000 Leafs. Tesla has sold an estimated 16,251 Model S cars in the U.S., according to Autodata Corp.
The Model S, which starts at $70,000, can go up to 265 miles on a single charge.
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