The Tesla Model S electric sedan was already unique among commercially available vehicles in having a quarter-inch armored plate protecting the whole bottom of the vehicle. Non-electric cars might not have a battery to protect, but they have a fuel tank. As explained here, car fires are a lot more common than most people think, with about 187,500 vehicle fires just on US highways in 2011. They just aren't newsworthy when they happen in non-Teslas...
Here's a search for "car fire" on Youtube:
Even after those accidents, Tesla maintained that the Model S was extremely safe, and that it took very violent accidents to cause the fires, and that despite these there had been no fatalities or serious injuries. An enviable record for any car, despite all the media frenzy.
Most companies would've left it there. "Our car is safe, let's wait for this negative attention to die down and move on..."
But Tesla tends to go the extra mile to serve its customers and inspire confidence. After all, their goal is not just to sell a few cars; they want to make electric cars mainstream and catalyze the rest of the industry. Anything that slows down adoption must be dealt with decisively.
"The odds of fire in a Model S, at roughly 1 in 8,000 vehicles, are five times lower than those of an average gasoline car and, when a fire does occur, the actual combustion potential is comparatively small," Elon Musk wrote. "Nonetheless, we felt it was important to bring this risk down to virtually zero to give Model S owners complete peace of mind. Starting with vehicle bodies manufactured as of March 6, all cars have been outfitted with a triple underbody shield. Tesla service will also retrofit the shields, free of charge, to existing cars upon request or as part of a normally scheduled service."
The new beefed-up EVs won't get just a slightly thicker armor plate. They'll get a titanium underbody shield and aluminum deflector plates!
Tesla performed 152 tests on these, and the new enhanced shields prevented any damage that could cause a fire or penetrate through the quarter inch "ballistic grade aluminum armor plate" that is already on the Model S. "We have tried every worst case debris impact we can think of, including hardened steel structures set in the ideal position for a piking event, essentially equivalent to driving a car at highway speed into a steel spear braced on the tarmac." So the underside of the Model S is now basically Fort Knox.
Here are some videos of the tests. First is a three-ball tow hitch:
Then a concrete block:
And an alternator:
For those who are worried that this new shield will impact the driving range, Tesla's tests show only a 0.1% impact (so basically impossible to notice without ideal testing conditions), and it also doesn't affect ride or handling.