After three recorded Model S electric car fires, The National Highway Traffic Safety Administration (NHTSA) is opening an investigation. Last month, the NHTSA said it would not investigate the fires, so what's changed? This time, Tesla Motors [NSDQ:TSLA] asked the agency to look into the matter.

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A Tesla blog post maintained that incidence of fires in the Model S is still lower than combustion cars, and noted that no one was injured in any of the fires. "However," the post said, "if a false perception about the safety of electric cars is allowed to linger, it will delay the advent of sustainable transport."

Tesla has also launched a software update for the Model S' air suspension system, which will give cars higher ground clearance at highway speeds. The company is also amending its warranty to include fire damage, even if it's the result of driver error.

The first fire occurred last month when a Model S driver hit a piece of metallic road debris near Kent, Washington. The owner got out unscathed and was impressed enough by the car's performance that he decided to buy another one.

A second fire occurred in Mexico after a driver reportedly jumped a curb at high speed and hit a tree. This one hasn't been quite as controversial, perhaps because it occurred outside the U.S., or because the driver may have been at fault.

LEARN MORE: Third Tesla Model S Fires: Still Not A Big Deal

The third incident happened in Tennessee. As with the Washington fire, the driver hit a piece of road debris, which apparently caused damage to the underside of the car and the battery pack.

Tesla CEO Elon Musk has defended the Model S throughout, noting that no one has been killed or injured in a Model S fire, and that fires are still an incredibly rare occurrence in the company's electric cars. Last week, he said the fires were caused by the severity of the accidents, and that Tesla would implement a fix if one were necessary.

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