There are skeptics who doubt that running over a large metal object could really trigger a battery fire, but there are electric vehicle experts who say it's entirely possible.
Tesla Motors says the dramatic fire happened after the driver struck a large metal object in the road. While it uses lithium ion batteries similar to ones that have caught fire spontaneously in laptops, jetliners and other electric vehicles, Tesla says this was not spontaneous at all.
Automotive technology instructor and department head Randy Bryant at De Anza College explained what probably happened. "Something hit the battery and caused a short circuit. And a lithium battery, if it's shorted, will cause extreme heat and could possibly catch on fire," he said,
Tesla's Model S battery compartment is housed in a steel case that covers most of the bottom of the vehicle. Inside, are 16 partitions containing millions of lithium ion cells. The battery pack is made at Tesla's Fremont plant.
"Tesla builds their batteries as many people do, in a compartmentalized state, so that this entire battery isn't just one great big lithium ion mass," said automotive analyst Brian Douglas.
The fire broke out in one of the front partitions and firefighters say it was a stubborn fire. They thought they had it out, but then it re-ignited. Tesla says the driver was out of the vehicle before the fire erupted.
The company commented on the incident saying, "The car's alert system signaled a problem and instructed the driver to pull over safely, which he did. No one was injured and the sole occupant had sufficient time to exit the vehicle safely."
The battery pack is low to the ground on purpose. "You want a low center of gravity in the car and this is obviously the heaviest component of this aluminum-bodied car. And the other reason is you may want to change that battery either to update it at some point in the car's future or, as some models have suggested, change batteries like filling a tank with gasoline," Douglas said.