Tesla’s rapid crash analysis; will NHTSA come in?
4 October 2013
On Tuesday, a Tesla Model S traveling at highway speed crashed into road debris, causing significant damage to the vehicle and resulting in a major vehicle fire. A video of the flaming wreck went Internet-viral (along with unwarranted EV fire hysteria), and Tesla stock shed up to $30 of its price per share at times during the next two days (about 15%). On Friday, Tesla Chairman, Product Architect & CEO Elon Musk posted a brief analysis of the accident and fire on the company blog. (The stock price began slowly climbing again.)
According to Musk and Tesla, a “curved section that fell off a semi-trailer ... appears to be the culprit. The geometry of the object caused a powerful lever action as it went under the car, punching upward and impaling the Model S with a peak force on the order of 25 tons. Only a force of this magnitude would be strong enough to punch a 3 inch diameter hole through the quarter inch armor plate protecting the base of the vehicle.”
...A fire caused by the impact began in the front battery module—the battery pack has a total of 16 modules—but was contained to the front section of the car by internal firewalls within the pack. Vents built into the battery pack directed the flames down towards the road and away from the vehicle.
When the fire department arrived, they observed standard procedure, which was to gain access to the source of the fire by puncturing holes in the top of the battery’s protective metal plate and applying water. For the Model S lithium-ion battery, it was correct to apply water (vs. dry chemical extinguisher), but not to puncture the metal firewall, as the newly created holes allowed the flames to then vent upwards into the front trunk section of the Model S. Nonetheless, a combination of water followed by dry chemical extinguisher quickly brought the fire to an end.
Musk goes on to point out that there are some 150,000 vehicle fires per year in the US, and asserts that the Model S, with its lower energy density battery pack, has a much lower “combustion potential” than gasoline-fueled cars.
An unknown at this point—mainly because of the shutdown of the Federal government—is whether or not the National Highway Traffic Safety Administration (NHTSA) will open a special investigation into the crash and fire, as it did with the Volt fire in 2011. (Earlier post.) That fire resulted not from a real-world crash, but was a delayed reaction to New Car Assessment Program (NCAP) side pole impact testing.
The resulting detailed investigation took about two months (earlier post). As a result of the investigation, General Motors modified the vehicle structure and battery coolant system in the Volt to further protect the battery from the possibility of an electrical fire occurring days or weeks after a severe crash. (Earlier post.)
At the time, NHTSA noted that:
NHTSA continues to believe that electric vehicles show great promise as a safe and fuel-efficient option for American drivers. However, as the reports released in conjunction with the closure of the investigation today indicate, fires following NHTSA crash tests of the vehicle and its battery components—and the innovative nature of this emerging technology—led the agency to take the unusual step of opening a safety defect investigation in the absence of data from real-world incidents.
(As a side note, the NTSB investigation and Boeing response into Li-ion fires on the 787 took about 3 months to work through before the FAA cleared the Dreamliner for flight again.)
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