I spoke with Doug Parks, GM's global vehicle chief engineer for the Volt, who started off by saying, "I believe the Volt has always been safe, but this was an event we needed to investigate thoroughly." After some sleuthing, they found the source of the fire was a short circuit caused by something called dendritic growth. The phenomenon occurs when energized silicon chips get wet and their metals are leached through the substrate, growing into what looks like tree roots that eventually lead to a short circuit. The battery in the Volt is shaped like a capital T, with the top of the T under the rear seats and the remainder running up the center tunnel between the front seats. During the test the undercarriage crash structure successfully absorbed crash energy but also punctured the battery case and cooling system. When the car was rotated, coolant worked its way onto the top of the battery, where a major control module lives, and got its silicon chips wet. Because the testing standards at the time did not require the battery to be discharged after the crash (analogous to draining the gas tank, which is standard practice), dendritic growth occurred and the chip short-circuited, connecting the poles of the battery and leading to a battery fire.
After repeated testing to replicate the scenario, GM found the probability of this happening in a real-life crash to be nearly zero but took preventive action anyway. The area of the battery tunnel around the crash beam was reinforced, and a coolant-leak sensor was added as well. All new Volts built since February come with these upgrades, and older cars can be taken in to dealers for what GM calls enhancements, since this isn't considered an official recall. Parks also noted, "The major automakers including GM are now working with the Society of Automotive Engineers to standardize discharge methods following an impact event." I've paid close attention to this story, and after reviewing the testing, failure mode, and response, I'm comfortable with the performance of the Volt in crash testing. As a final thought, consider this: Traditional cars tote around 15 gallons of highly flammable (and carcinogenic) gasoline in an easily pierced tank under the car, yet you don't even think about it.
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