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 had an '88 Dodge Shadow that went up in flames in my driveway. The fuel system had a small leak on top of the engine, I wasn't yet sure which connection it was coming from and it didn't look serious enough to worry about so I drove the car to work one more day. After the fact, I remember the engine backfired right when I shut if off back home. That must have been when it lit the leaking gasoline on the intake manifold. A few minutes later I was inside checking my email when I hear what sounded like a couple car doors slamming shut, so I go outside expecting to find someone out there. My car had flames rolling up the windshield from underneath the hood and there was a pool of burning gasoline on the ground in between the front tires. I grabbed a garden hose and tried to put it out but it seemed to be getting worse and then I saw that the windshield was cracked and the car was likely totalled. So I paused to evauluate the situation, that's when I realized the fuel pump was on and pumping gasoline into the fire. I tried to get the hood open but the release cable had melted apart, there was no way to reach the battery from underneath and it would take too long to find something to cut through the hood. So I got in the car and let off the parking brake, put it in nuetral and rolled the car back down the driveway. Reset the parking brake and got back out fast as there was a lot of heat coming through the windshield. The door was wide open the whole time I rolled it back. Then I thought to go underneath the back of the car where the fuel tank is, and pull the wires coming off of the tank. I couldn't get the connector apart so I just pulled hard enough to break the cable apart. This disconnected the fuel pump, and stopped adding fuel to the fire. I later discovered that the relay that controls the fuel pump has it's wiring running right behind the engine along the top of the firewall, so that it can be run down the opposite side of the car from where they decided to put the relay. This wiring had melted together and shorted during the initial fire, this in turn kicked on the fuel pump and made a small fire into a very serious fire. I was able to get the fire out after cooling it down from all sides. That car was a total loss. The radiator was half melted, firewall looked like it had buckled, adhesive along the bottom of the windshield had started to disintegrate. Carpet inside the car was scorched. Nowdays, I find myself considering the routing of wiring like that on other cars.
Yes, let's maintain perspective. Let's not allow unsafe vehicles on the road just because they are relatively new. Steps need to be taken to minimize the damage to batteries in a accident or to limit the resulting fires!
Napaerlou, what is 'not true'? That car fires still occur? That fuel is combustable? That we don't need perspective? Here's some perspective for you;
From the NFPA; In 2003-2007, U.S. fire departments responded to an average of 287,000 vehicle fires per year. These fires caused an average of 480 civilian deaths, 1,525 civilian injuries, and $1.3 billion in direct property damage annually. (Issued in June 2010)
I see no correlation between my examples and Tesla, except that they were car fires caused by unique situations. I base no strong conclusions based on any single incident.
Sure, cars are much safer than in the past, but how much safety must be demanded, particulary from a lone case? Although I'm sure NHSTA is having discussions about this, presumably they will have to have a larger data base than one to justify major changes to testing. Far as I know, the NHSTA does no testing of debris puncture of undercarriages or fuel tanks, on any car.
In this age, the most unsafe and deadly thing about any car out there is the driver, and we demand precious little testing of them.
I wonder if Tesla will replace this guy's car under warranty?
I've been involved in designing machines using sizeable Lithium Ion batteries. We've had a couple "thermal events". It's not a pleasant thing.
I've also witnessed car fires in gasoline powered vehicles. In fact one burned in my driveway years ago. As a foolish teenager I got in the vehicle and put it in neutral and rolled it back from the house. I then put it out with an extinguisher.
We get all worried over a battery fire, but we don't think twice about carrying around 20 gallons of gasoline. Ever witnessed a car fire? If the fire spreads to the tank it's lights out. Typically however, the fires starts in the engine compartment and never reaches the tank in the back of the vehicle. There's usually enough fuel pressure in the lines to create a nice fire in the engine compartment anyway once things start melting. That's when tires explode.
Electric car manufacturers are going to have to find ways to protect the batteries. The massive size of the batteries tends to mean they are distributed throughout the vehicle. This complicates the safety aspect. But they'll figure it out, it'll end up being a compromise -- like every engineering decision -- between cost, risk, and performance.
When I read your post, I found myself humming the 'Speed Racer' theme song (from the cartoon, not the abomination of a movie). I pictured the hydraulic jacks popping out at the press of a button on the steering console and the sound effects ''don-don-don-don-don" as the vehicle pole-vaulted away from the flaming battery.
The unfortunate drawback of your suggestion is that there would need to be a fire sensor in the battery compartment to jetison the flaming cells and then the car behind you would not only hit the metal piece but also run over the flaming battery. That is not a very safe thing either, considering the car behind you would likely be a gasoline powered model. A safer mechanism might be a fire suppression system with a battery cutoff so the car stops and you know to get your ass out of and away from the vehicle. Of course, the best bet would have been for the driver to NOT hit the metal object in the road, but if you can afford to buy a Tesla Model S, you have enough dollars not to need common sense (pun intended). Maybe Tesla needs to re-examine the road clearance and either raise it, or put a metal skid plate on the bottom to protect the battery compartment. Yes, that would increase the mass of the car and decrease the ability to get those super-fast highway speeds that Tesla loves to market, but hey, don't you want your customers to buy a second car from you? They can't do that if they die in the first one!
Ken E., that is not true. Car fires in many models of car were a great concern in the past, especially fire on impact. Remember the Ford Pinto in the 1970s. Just looking this up in on the web, there is recall on Ford trucks from 1997 t0 2003 becuase of concerns about a fuel tank straps that could be a problem in high corrosion areas. There certianly is concern about fires in cars, and they have become much more safe. It is a problem, but many car fires are like the first one you mention. This is a concern, but based on the number of vehicles and miles driven, it is not as big an issue as it might be with the Tesla. Also, the chemicals involved in the Tesla fire are a lot more dangerous. Based on your examples, one would conclude that the Tesla battery placement is badly flawed and it will be interesing to see how the NHSTA deals with it.
Eject the Lithium! - just like the Enterprise (NCC-1701) can eject the warp core along with the di-lithium cystals in case everything goes to hell in a hand basket. Impulse power only to maneuver away from the core.
As I stated when people were crowing about the 5* rating of the Tesla. that the tests were based upon tests written and designed for common ICE failures. Many of the tests were added after failures on the road of vechiles. example (rollover -jeeps, reend collisions-Pinto). They have not updated their tests for the specific dangers presented by Battery vechiles. Many of which will not be know until tens of thousand of units are on the roads for years.
Kinda of scary but also sadly how it works. We know batteries can melt down from minor damages, that is what caused this fire. What other failures are out their that we do not know and may not know for 3-10 years
The question of whether engineers could have foreseen the shortcut maintenance procedures that led to the crash of American Airlines Flight 191 in 1979 will probably linger for as long as there is an engineering profession.
More than 35 years later, the post-mortem on one of the country’s worst engineering disasters appears to be simple. A contractor asked for a change in an original design. The change was approved by engineers, later resulting in a mammoth structural collapse that killed 114 people and injured 216 more.
If you’re an embedded systems engineer whose analog capabilities are getting a little bit rusty, then you’ll want to take note of an upcoming Design News Continuing Education Center class, “Analog Design for the Digital World,” running Monday, Nov. 17 through Friday, Nov. 21.
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