The vision of a car ablaze is startling. As the number of hits on the burning Tesla video climbed over two millions, people inevitably began to raise safety concerns. Elon Musk, the founder of Tesla Motors, responded on the company's blog with some facts about the damage sustained in the accident, the construction of the vehicle's battery, and the resulting fire.
Musk explained that damage to the armor plating on the bottom of the vehicle was inflicted by contact with debris of a specific shape that resulted in a lever action, puncturing the bottom of the Model S. He noted that 25 tons of force would be required to make the three-inch-deep puncture in the quarter-inch-thick armor plating.
Don Sadoway, a professor of materials chemistry at MIT and a leading advanced battery technology and energy storage expert, says that this event is incredibly rare. "Large format batteries are not intrinsically problematic and can be made to stand up to abuse, and I view this situation as an outlier event. The chances of running over something that actually punctures the underbelly of a car are small."
Upon detecting the puncture, the car's control system warned the driver to pull over and exit the vehicle, which he did without injury. At that point, fire broke out in one of the car's 16 battery modules. Musk pointed out, "At no point did fire enter the passenger compartment." This statement was true even after fire department personnel punctured the firewall in order to allow the fire to spread upwards, as seen in the video.
To further relieve fears of battery fires, Musk went on to compare the combustion potential of the Model S battery system to a typical internal combustion engine. "In contrast, the combustion energy of our battery pack is only about 10 percent of that contained in a gasoline tank and is divided into 16 modules with firewalls in between," he noted on the blog. "As a consequence, the effective combustion potential is only about 1 percent that of the fuel in a comparable gasoline-powered sedan."
Citing the National Fire Protection Association's statistics, Musk explained that combustion engines currently experience fires at a rate of one fire per 20 million miles driven. In contrast, Tesla has shown one fire per 100 million miles driven.
Sadoway agrees with that assessment, and says that this incident should not be a deterrent to adoption rates. "Unfortunately, we do see cars catch fire. There are accidents regularly where you see highly volatile fluids pouring out onto the road and catching fire. That doesn't stop people from buying them though. If you open the newspaper and see that there was a collision and that one car caught fire, you might say, 'Wow, that is too bad,' then go out and hop into your car and drive. If it is new technology that it happens to, people pay more attention.
"From my perspective, the bigger problem with lithium batteries is the cost. You don't see them widespread because the cars that are purely electric right now are far too costly to appeal to the general public. They won't have that attraction until we get one on the showroom floor for a total less than 20 thousand dollars.
How did the warning system work in Tesla? Did it detect the mechanical failure of the armor and infringement into the battery? Or did it detect a "battery over-heating" scenario after the punch was made and detect a possible fire (which I am guessing)? If the warning system is designed to detect infringement of the battery armor, this is incredible.
The last two paragraphs of this post are missing a quotation mark. It's not clear whether the author or Dr. Sadoway offered the opinion that EVs need to cost under $20k. Whoever did, that's an oddly high bar to meet when you consider the drastically reduced operational costs of EVs--fuel less than half the cost of that for a Prius and almost no maintenance required at all. Moreover EVs are smoother and quieter than any ICE on the road at any price, at least as self-generated (immunity to outside noises and suspension being independent of drivetrain). The market has already placed a high cost premium on those qualities. People just need to learn that and need to feel comfortable with adapting to something different. Human nature is against doing that.
In my opinion the technology obstacle is that battery development needs to be improved to allow an honest 200 miles of range with very little degradation over 200k miles or so. It may take a solid state battery or something else more stable. If the masses cannot feel comfortable paying the price of having to recharge overnight after "only" 200 miles in order to rid themselves of the drawbacks of fossil fuels, then our addiction to oil may indeed be fatal to humanity.
The number of fires per mile is not the statistic I think you need to consider. The number of petrol tank penetrations to battery penetrations is what you want to compare.
I'll bet there are many more petrol tank penetrations where gasoline is spilled and there is no fire. Unfortunately where a battery is concerned, most penetrations (where the physical cell is compromised) are likely to self ignite. That is why they had to put the extreme reinforcing on the base and between cells as firewalls.
For EV batteries you need to consider
1. There is a self ignition capability (chemistry or physical pack faults)
2. There is an immediate fire capability if the chemistry/construction is compromised
Tesla, if successful will produce millions of batteries to build into their EV packs, and just like laptop batteries they will have a failure rate above zero. Unfortunately, any failure may result in very large uncontrolled energy discharges almost guaranteed to have an associated fire (or as in the Boeing experience, heat destruction and smoke).
While gasoline tanks are an obvious potential fire hazard, it is not a given that every fault will result in fire. IMHO Hydrogen (metal hydride) storage is probably safer than either gasoline or any of the battery chemistries.
When a video goes viral, a sample size of one takes on an extraordinary weight in the public eye. Scientific explanations (regardless of how accurate) have a tough time competing with an iconic image that is seared into the mind. That said, it was very interesting to read the "rest of the story".