In GM's terms, the process of "depowering" a Volt is the act of manually disconnecting the battery's flow of energy from the rest of the vehicle after a crash. And a rather serious crash at that--depowering might as well be the equivalent of giving your Volt its last rights. It's performed only by GM's internal team.
When To Depower?
For owners, the logical question becomes: when does my Volt need to be depowered? After a fender bender, a rear-end collision, or something even more serious, like a rollover accident?
"The vehicle would most likely have to be totaled," said Rob Peterson, GM's spokesperson for the Volt. "Simple fender benders will be not impact the battery."
"It's highly unlikely that a Volt would be drivable following a rear or frontal crash that resulted in damage to the battery," said Peterson. "The battery is located between the front and rear axles; i.e. it's highly protected."
The recently reported fire of a NHTSA-tested Volt happened three weeks after a rather strenuous series of crashes, and a proper depowering apparently wasn't performed. GM had yet to finalize the Volt's battery depowering procedure prior to the first NHTSA crash tests that resulted in fire, despite the car already being on sale.
Thankfully, the question of when to depower is moot for Volt owners today because GM's OnStar system (free for three years with the purchase of a Volt) tracks inbound alerts when the car's airbags deploy. If an accident involving a Volt is deemed serious enough, the company sends engineers to the vehicle.
"The vehicle, along with notifying OnStar that an airbag has been deployed, would also send key data that can be used by the engineering team to understand the area and impact of crash to the vehicle," said Peterson. "Engineers can use this data to determine if the battery was potentially compromised and requires evaluation."
And after three years, when the OnStar subscription runs out? Peterson says GM is evaluating its OnStar plans for Volt owners and points out that it's likely there will be an entirely new protocol in place for depowering at that time. The company says it is working with the Society of Automotive Engineers and other manufacturers on industry-wide protocols for post-crash EVs.
Nissan Says Leaf Doesn't Need To Depower
Like the Volt, the Nissan Leaf uses airbag deployment as one of its trigger mechanisms for safety notifications. But the Leaf and Volt have many differences--not the least of which is that the Chevrolet's battery is liquid cooled, while Nissan's is air cooled. Nissan reps are quick to point to this as a simpler and less expensive architecture. They also claim that Nissan doesn't need to send its engineers to a Leaf crash site, because its disconnection procedure happens onboard the vehicle itself.
"The Nissan Leaf is designed with battery safety systems that disconnect the high voltage from the vehicle in a severe crash," said Tim Gallagher, Nissan Senior Manager of Corporate Communications. "The Leaf is not required to be 'depowered' after a crash."
"When there is a crash that involves the airbags, the airbag control unit sends a signal mechanically to the battery and disconnects the modules."
All the same, Nissan published a guide for first responders that details procedures for handling a damaged vehicle at the scene of an accident, including a manual high-voltage system shutdown, rather than the automatic process described above.
The forthcoming results of the NHTSA's investigation into the Volt fire, however sensational they might appear, will likely prove to be another building block establishing normalcy around EVs. Until then, owners of vehicles with lithium batteries on board should do what they've always done: drive them, love them and treat them like, well, normal cars.
If you're in an accident with an electric vehicle, follow the NHTSA's guidelines:
• Consumers are advised to take the same actions they would in a crash involving a gasoline-powered vehicle-exit the vehicle safely or await the assistance of an emergency responder if they are unable to get out on their own, move a safe distance away from the vehicle, and notify the authorities of the crash.
• Emergency responders should check a vehicle for markings or other indications that it is electric-powered. If it is, they should exercise caution, per published guidelines, to avoid any possible electrical shock and should disconnect the battery from the vehicle circuits if possible.
• Emergency responders should also use copious amounts of water if fire is present or suspected and keeping in mind that fire can occur for a considerable period after a crash should proceed accordingly.
• Operators of tow trucks and vehicle storage facilities should ensure the damaged vehicle is kept in an open area instead of inside a garage or other enclosed building.
• Rather than attempt to discharge a propulsion battery, an emergency responder, tow truck operator, or storage facility manager should contact experts at the vehicle's manufacturer on that subject.
• Vehicle owners should not store a severely damaged vehicle in a garage or near other vehicles.
• Consumers with questions about their electric vehicles should contact their local dealers.