Tesla adds titanium shield to prevent Model S battery fires, ending federal probe

Following three reports last year of fires from punctured battery packs, Tesla Motors today revealed updates to its all-electric Model S sedan that it says should eliminate the chance a piece of road debris could cause a fire. The solution: More armor, including a titanium plate that the company's own tests show can withstand impacts from steel and concrete — an answer that was good enough for federal auto safety officials to close a probe without finding a defect.

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In a public letter, Tesla CEO Elon Musk repeats his claim that the Model S is the safest vehicle on the road, noting that with some 35,000 cars in service there have been no deaths or injuries to date. But he's also careful to present the changes as upgrades rather than a safety improvement — which would trigger the legal requirements of a recall.


"We felt it was important to bring this risk down to virtually zero to give Model S owners complete peace of mind," Musk said.

But the changes also come after the National Highway Traffic Safety Administration opened a probe into the two fires; unlike other electric cars, Tesla mounts its battery pack on the bottom of the chassis, exposing it to more road debris.

Tesla says the new triple underbody shield went into production March 6, and will be offered to all current Model S owners who ask for it. It consists of three pieces: an aluminum bar just ahead of the battery pack, a titanium cover for the pack itself and an additional aluminum shield that will push the car up over anything strong enough to survive an impact with the first two devices. Musk says the company ran 152 tests on the new armor, and nothing it could find penetrated the batteries.

"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," Musk wrote. As you can see above, a concrete post under the shield gets crushed to powder; a tow hitch and an alternator thrown under the car meet similar fates.

Two of the three fires reported last year were later traced to road debris; the third came from a crash in Mexico where the driver had been going 110 mph before hitting a wall, ripping the wheels from the car. I

In a notice Friday, NHTSA says the changes "should reduce both the frequency of underbody strikes and the resultant fire risk," and closed its probe, saying no safety defect exists in the Model S.

Musk says the new pieces will have a minimal effect on the range of the Model S. And Tesla's customers have brushed off the fire reports as flukes; sales have continued to grow beyond what Tesla can supply. Getting ahead of your problems would seem to be a strategy that other automakers could learn from.

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