A Tesla Model S electric car caught fire after hitting road debris on a Tennessee freeway, the third fire in a Model S in five weeks.

The blaze last week near Smyrna, Tennessee, 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.

In early October, a Model S 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, California, fell 7.5 per cent to US$139.77 on the news. That was on top of a plunge of 14.5 per cent the previous day, 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 per cent this year.


The Model S has a large battery pack under the passenger compartment, protected by a 6.3mm-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 US Government's car safety watchdog, says it will contact Tennessee authorities to determine if there are safety problems that need further action. The agency 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 on to an emergency lane and escape. Tesla 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 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 US$120,000.

According to the US Fire Administration, there are around 194,000 vehicle fires on US roads each year. The majority - 61 per cent - start in the engine area, while 15 per cent start in the passenger area. Approximately 300 people die and 1250 are injured in US vehicle fires each year.

Most happen in petrol-powered cars. Electric vehicles are less than 1 per cent of the cars sold in the US.


General Motors' Volt and Nissan's Leaf are the top-selling electric cars in America. A Chevrolet Volt caught fire two years ago after a government crash test, but the investigation into the incident was closed after GM agreed to a safety campaign to bolster shielding around the battery.

GM has sold more than 50,000 Volts in the US since late 2010, Nissan has sold almost 38,000 Leafs, Tesla has sold an estimated 16,251 Model S cars.