A CT scan image of a battery cell shows breakdown of layers directly below an indentation. A recent report from Underwriters’ Laboratories Inc. suggests that such dents in the casing are a possible failure mechanism for lithium-ion batteries. “The resulting high stress/strain will lead to a mechanical failure of the separator (with failure of the casing), allowing for direct contact between electrodes at a distance only a few layers below the casing surface,” the report says. (Source: Underwriters Laboratories Inc.)
I would imagine that all of the tests that Tesla got a high rating for were for crashes at various speeds and angles which are of course typical for a car and all front, rear or side.
If the failure mode has been correctly anticipated one should point out that this sort incident downed a Concorde in France a few years ago. There a fragment of a previous landing of a different plane was catapulted up by a tyre and hit the underside of the wing and a piece of that splintered off and ruptured a fueltank or line.
The problem here is that floor strikes have traditionally not been an issue for cars with the tank sitting high to the rear and if it did leak it had to be combined with sparks for a disaster. With a battery of course sparks are a given.
From memory when I saw the Tesla tear down the battery was almost integral to the frame.
BTW, one of the tests that they do when an airbag module is being calibrated here is to hit the floorpan with a hammer really hard to ensure there is no deployment. I wonder if Tesla does that.
Which reminds me, I was driving this past weekend and slammed my floorpan on the ground due to the road being a little uneven and nothing much happened. It seems to me that the vertical impact strength of the Tesla battery would have have meant that it did not come off so lightly.
I've seen many a car fire in my lifetime, even experienced a minor one.
I saw a brand new Corvette burn down to the block, frame, and rims that had been been in a ticker tape parade for a world series win. (A pile of shredded paper it had plowed over started on fire underneath it.)
There was an accident in Chicago a few years back where a van full of kids was engulfed in flames because of road debris which punctured the fuel tank.
Car fires of varying degrees occur every day somewhere in America, without people clamoring for safety changes. Let's keep in perspective that the fuel load of any ICE powered car can be every bit as bad, and these thin fuel tanks are often less protected than the Tesla battery. The sky is not falling on Tesla because of one incident.
So the Pinto, Chevy saddle tanks, and the recent Jeep recalls should all be put aside if we let the Tesla get a pass?
On the otherhand, debris is a part of the road. If consumers expect the cars to be 100% safe, then the only solution is to get rid of the car. At least in this instance, the driver was able to pull over and get out. In fact, I think this was explicitily discussed when many here at DN were critical of the Boeing batteries. Lithium ion chemistry in an airplane, not so good as the option is a plane crash (or crash landing). But in an automobile one could pull over and get out of the car.
Wow that is scary stuff! It's unfortunate this keeps happening, because it certainly isn't going to do anything to promote the use of hybrid vehicles and EVs. It's especially troubling because of Tesla's high rating, as Lou points out.
apparently the battery has an armor plate beneath it, 1/4" thick. However,
hit something hard enough, fast enough and it will rip through almost anything.
Lets not forget some minor ice sank the Titanic.
Now that said, Lou's idea of dropping the battery pack isn't neccessarily a bad idea.
if you have a fire, it would seem easiest to have some explosive bolts on the body side, that would cut the structural attachments and let the battery drop off. You would need a small internal battery to drive away, but, it could be done as a future upgrade.
"Such occurrences are rare, however. A Tesla spokeswoman told Design News that the Model S has collectively been driven 83 million miles at this point, with dozens of known accidents, and no such battery problems, until now."
Seems to me that this is a misleading statement and is a poor defense for Tesla battery safety. 83 million miles refers to driving distance but does not take into account an impact with an object - and "dozens of known accidents" does not give any quantifiable data regarding this specific issue.
Ken, my understanding of the battery swap out machine is that it simultaneously unscrews a large number of bolts, drops the battery down, then raises another battery up into place. Reportedly, it is the same piece of equipment they use in the factory. It is not a mobile piece of equipment. In videos of it working, the car is driven up over the device. This is not a quick relesae mechanism. The device reportedly will cost Tesla $500K to intsall.
If the battery is susceptible to being breached the way this one was, any auxiliary battery would be susceptible as well. If it was anywhere near the part tha caught fire, it would also catch fire. Also, the battery weighs over 900 lbs., so I am not sure your idea would work.
I think the idea of having the battery basically cover the bottom of the car is a very bad one. This could prove their undoing. Now they will probably have to put some sort of shielding there. That will increase the weight even more.
Using sensors and a specialized test stand, engineers have discovered that the root causes of head trauma may lie in a complex pattern of forces that today’s football helmets aren’t equipped to handle.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.