Intense Scrutiny of Tesla Model S Fires Exceeds Evidence of Mechanical Problems

By · January 02, 2014

Kent, Washington Tesla Model S fire

Tesla Motors has taken on a huge task in leading the way on electric vehicle development. This has brought intense scrutiny with the rollout of the Model S, and while reviews of that car have been overwhelmingly positive, in some quarters Tesla and the Model S have drawn huge criticism. On motoring.com.au, Michael Taylor says his biggest gripe for 2013 is the “vilification of Tesla for a handful of fires” which he describes as maliciously orchestrated, and asked, (referring to the Tucker Car Corporation,) “Are they trying to turn Tesla into the new Tucker?”

We don’t know of any way to prove there is a conspiracy to discredit Tesla Motors, but as Taylor says the response to the four Tesla Model S related fires are out of line with the response to equivalent gasoline car fires. Over on Seeking Alpha, Juan Carlos Zuleta claims that everyone in the automobile industry is afraid of Tesla Motors because the company is executing its plan extremely well and is realistically on track to producing 500,000 electric cars a year from their factory in Fremont, CA. It’s a small stretch of imagination to say some organizations would take action to quash Tesla.

With that in mind let’s review the Model S fires to see if there is a serious flaw that bodes ill for Tesla’s future. The fires were (in order):

  • Kent, WA, a Model S battery pack impaled by road debris, with fire resulting from short circuiting in the battery pack leading to fire.
  • Yucatan, Mexico, a late night high speed (over 100 miles/hr) crash where a Model S smashed through a concrete wall, hit a tree, before bursting into flames.
  • Nashville, TN, another Model S battery pack impalement
  • Irvine, CA, a garage fire related to using the Universal Mobile Connector

Garage Fire

The garage fire occurred in November, and a Reuters report citing an Orange County Fire Authority is getting widely referenced for this quote from the OCFA: "The fire occurred as a result of an electrical failure in the charging system for an electric vehicle." The OCFA report went on to say investigators could not conclude a cause for the fire, and that "The most probable cause of this fire is a high resistance connection at the wall socket or the Universal Mobile Connector from the Tesla charging system." A statement provided by Tesla Motors likewise said that the Model S itself was not the cause in the fire, but:

"Based on our inspection of the site, the car and the logs, we know that this was absolutely not the car, the battery or the charge electronics. There was a fire at the wall socket where the Model S was plugged in, but the car itself was not part of the fire. The cable was fine on the vehicle side; the damage was on the wall side. Our inspection of the car and the battery made clear that neither were the source and were in fact functioning normally after the incident. In addition, a review of the car’s logs showed that the battery had been charging normally, and there were no fluctuations in temperature or malfunctions within the battery or the charge electronics."

Garage fires are fairly common, so we wonder why a garage fire, in a garage that happened to contain a Tesla Model S, is worthy of international news coverage. It’s not like garage fires never occur, so why is this fire treated differently than other garage fires? According to the National Fire Protection Association, 13% of home fires were electrical fires, which resulted in 18% of civilian (non-firemen) deaths and 21% of property damage.

If, though, the Universal Mobile Connector is flawed and prone to causing fires, that would be worthy of some news coverage. Indeed, over on the teslamotorsclub.com forum, many Model S owners report overheated and melted Universal Mobile Connectors. Tesla is already on its 2nd generation UMC design, and has been quietly replacing customers’ UMC’s. Further, there's a hint that a 3rd generation UMC design is on its way.

Tesla Motors isn't the only automaker to have this problem. Back in early 2012, GM replaced the portable EVSE's for the Chevy Volt because of overheating and melting complaints from owners, replacing them with units that had thicker wires. If there is a flaw in the UMC design, Tesla is doing the sensible thing, as did GM before them, in redesigning and replacing the charging equipment.

Car Fires

Nashville, TN, Model S fire

What about the Tesla Model S car fires while in operation on the road? The crash in Mexico is obviously a fluke, where we’re surprised anyone survived at all, but not only did the occupants survive, they were able to flee the scene.

The two Model S impalements have the appearance of repeatability. Seemingly, any Model S driven over road debris could have that debris lodge between the road surface and the battery pack, puncturing the pack, and producing a fire. The ¼” aluminum plate protecting the Model S battery pack, while a good idea, clearly wasn’t enough to prevent impalement and fires in every circumstance. The short-term fix Tesla sent out, to adjust the ride height, is sensible because it lessens the likelihood of metal debris lodging between road surface and battery pack.

As with the garage fire incident, the coverage of the two Model S impalements are far in excess than coverage impalements of gasoline powered cars or car fires. Impalements by road debris do occur, sometimes with deadly results. In 1991 a German tourist driving his family near Elko, NV, died after an impalement. A tire jack on the road flipped up through the floorboards, impaling him in the groin. He was able to safely drive the car to the side of the road, but died shortly afterward. A lot of road debris is thought to have fallen off trucks when drivers don't securely tie down loads, which is called a "leaking load." In another incident, a piece of rebar skewered the rear passenger door of a car, and while nobody was hurt there could have been injury if it had skewered the car elsewhere.

Battery Pack Flammability

The question on everyones lips, however, is whether the Model S battery pack is explosively flammable, and whether it’s a risk. Unfortunately this specific question is difficult to answer because there don’t seem to be studies available to the public of the battery cells Panasonic sells to Tesla Motors. Generally speaking, lithium ion battery flammability depends on the specific chemistry of a pack. A 2012 paper for the Electrochemical Society says it's about the thermal stability of the electrolyte and other battery components. Heat a lithium ion cell to a high enough temperature and it will catch fire, but that temperature depends on the chemistry. One way to cause heat is to short-circuit part of the pack, such as by impalement.

Do these two fires mean Tesla’s engineers totally flubbed the Model S design? No. Instead, we see that Tesla’s engineers successfully designed the Model S to minimize fire risk to the occupants. The Model S battery pack has firewalls between segments of the pack, to minimize the spread of fire and to channel fire toward the front of the car. This means the whole battery pack is unlikely catch fire, but with the side effect of scary-looking walls of flame shooting out the front of burning Model S's. The result is that passenger compartments weren't much impacted by fire, which could be important to passengers who might be unable to quickly exit the vehicle.

The NHTSA is investigating the Tesla Model S, and it’s possible the investigators will come up with an actual flaw in the Model S. What we know so far though are two things. First, Tesla’s engineers are proactively working to fix problems. Second, common occurrences (impalements, car fires, garage fires, high speed wrecks) get extraordinary news coverage when they occur to a Tesla Model S. We shouldn’t be surprised, the Chevy Volt firestorm two years ago had news coverage so over the top that GM CEO Dan Akerson quipped that while GM’s engineers had designed one of the best cars in the world, they hadn’t designed it to be a political punching bag.

It is a fair question to ponder. Are those who stand to gain from the electric car being "killed" again actively trying to undermine the companies who are furthest along with electric cars?

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