Tesla Motors Inc (NASDAQ:TSLA) chairman, CEO, and product architect Elon Musk has responded to what caused the fire on the Model S that was reported earlier this week. A curved section that fell off of a semi-trailer was recovered from the roadway near where the accident took place and that seems to be the culprit for the accident. Based on the geometry of the object, there was a powerful lever action as it went under the Model S vehicle. It punched upward and impaled the Model S with a peak force of around 25 tons. Based on a force of this magnitude, it was strong enough to punch a 3-inch diameter hole through the quarter inch armor plate that protects the base of the Model S, according to Musk in a blog post.
“The Model S owner was nonetheless able to exit the highway as instructed by the onboard alert system, bring the car to a stop and depart the vehicle without injury. 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,” said Musk. “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.”
The fire did not enter the passenger compartment. It all stay within the internal firewalls built in the pack structure of the vehicle. If this same situation happened to a traditional gasoline car, the result could have been much worse. Typical gas cars have a thin metal sheet that protects the underbody, which leaves the fuel supply lines and fuel tank vulnerable.
There are 150,000 car fires per year, according to the National Fire Protection Association. Americans drive 3 trillion miles per year. This means that there are 1 vehicle fire for every 20 million miles driven, compared to 1 fire in over 100 million miles driven in a Tesla vehicle.
Musk also reprinted the e-mail correspondence (with permission) that Tesla Motors VP of sales and service had with the owner of the vehicle, Robert Carlson:
From: robert Carlson
Sent: Thursday, October 03, 2013 12:53 PM
To: Jerome Guillen
Subject: carlson 0389
Thanks for the support. I completely agree with the assessment to date. I guess you can test for everything, but some other celestial bullet comes along and challenges your design. I agree that the car performed very well under such an extreme test. The batteries went through a controlled burn which the internet images really exaggerates. Anyway, I am still a big fan of your car and look forward to getting back into one. Justin offered a white loaner–thanks. I am also an investor and have to say that the response I am observing is really supportive of the future for electric vehicles. I was thinking this was bound to happen, just not to me. But now it is out there and probably gets a sigh of relief as a test and risk issue-this “doomsday” event has now been tested, and the design and engineering works.
On Oct 3, 2013, at 12:29 PM, Jerome Guillen wrote:
Dear Mr. Carlson:
I am the VP of sales and service for Tesla, reporting directly to Elon Musk, Tesla’s CEO.
I am sorry to hear that you experienced a collision in your Model S 2 days ago. We are happy that the Model S performed in such a way that you were not injured in the accident and that nobody else was hurt.
I believe you have been in contact with Justin Samson, our service manager, since the accident. We are following this case extremely closely and we have sent a team of experts to review your vehicle. All indications are that your Model S drove over large, oddly-shaped metal object which impacted the leading edge of the vehicle’s undercarriage and rotated into the underside of the vehicle (“pole vault” effect). This is a highly uncommon occurrence.
Based on our review thus far, we believe that the Model S performed as designed by limiting the resulting fire to the affected zones only. Given the significant intensity of the impact, which managed to pierce the 1/4 inch bottom plate (something that is extremely hard to do), the Model S energy containment functions operated correctly. In particular, the top cover of the battery provided a strong barrier and there was no apparent propagation of the fire into the cabin. This ensured cabin integrity and occupant safety, which remains our most important goal.
We very much appreciate your support, patience and understanding while we proceed with the investigation. Justin keeps me closely informed. Please feel free to contact me directly, if you have any question or concern.
Jerome Guillen I VP, WW sales and service