Engineers have been designing electric vehicles for years with electrical isolation technology to cut off power from EV batteries in the event of a crash to prevent electrocution of first responders or occupants and to lessen the chance of a fire.
Recent crash tests by the independent, nonprofit Insurance Institute for Highway Safety on the 2021 Volvo XC40 Recharge and the 2021 Ford Mustang Mach-E bore out that such battery cut-off technology was working as designed along with other systems to prevent deadly crumpling of the passenger containment area of the vehicle.
Such technology designs have become increasingly important as EVs gain interest from global vehicle manufacturers who want to attract buyers and as the Biden administration pushes for 500,000 more U.S. charging stations for EVs in coming years.
A recent Tesla crash that killed two men near Houston also is being probed by federal officials partly because the vehicle kept burning well after the crash, taking first responders four hours to extinguish. The inquiry will look at the problems putting out the fire, but also whether the semi-autonomous Autodriver feature was working.
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The National Transportation Board issued a report in November on the safety risk to emergency responders from Lithium-Ion battery fires in EVs.
In a Youtube live event streamed May 5 by IIHS, a senior crash test coordinator said Lithium-Ion fires have been known to occur in EVs weeks after a collision as the crashed vehicle sat apparently undisturbed in a scrap yard.
General Motors recently announced plans to install EV battery diagnostics onboard in all its future EVs after facing a recall of 69,000 Bolt hatchbacks from 2017 to 2019. Five of them had caught fire and two people suffered smoke inhalation and a house was set ablaze.
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IIHS test coordinator Sean O’Malley said its EV crash tests, including the recent ones conducted on the Ford and Volvo, used IIHS-designed tools to verify that the battery power was indeed cut-off when the crashes occurred. Most EVs generate 350 to 400 volts and are made up a series of smaller batteries grouped together in modules that together form a flat compartment that covers the floor of the vehicle.
“Anything over 60 volts is considered high voltage,” he said from the IIHS test facility in Ruckersville, Virginia. “If you were to grasp the vehicle without a glove on, and it was electrified, your muscles would tense up so much you wouldn’t be able to get yourself off the car,” O’Malley said. IIHS ties off its technicians examining a test-crashed EV with a fiberglass pole to pull them away in the event of an electrification.
The crash tests for EVs are similar to those for gas-powered vehicles except for the electrical isolation test, which replaces a test in a gas-powered vehicle to ensure a fuel pump is shut off after a crash to limit the possibility of a fire.
“After a crash we want to make sure that the battery… has been disconnected,” O’Malley said. “Instead of a fuel pump being shut off [in a crash of a gas-powered car] when an airbag deploys, a switch or a fuse is blown in the battery itself, cutting off the voltage to the vehicle.” In an IIHS crash test, any vehicle crashed that did not cut off voltage would be receive a “poor” rating, the lowest rating.
After a test crash, IIHS checks for electrical isolation then also uses thermocouples connected to the battery case and a thermal imaging camera to check for hot spots. “We’re just looking for any kind of quick, accelerated increases in temperature,” he said. “At 78 degrees, the alarms will go off from the thermal couples and we’ll move the vehicle outside where the fire department will be waiting.”
IIHS has not experienced any “thermal runaway events” or an electrical problem in its testing of EVs so far, but has procedures in place for emergency response in the event one occurs. EV crash tests have gone back to as far as 2011, when IIHS tested the Chevy Volt and Nissan Leaf. The Tesla model S was tested in 2016 and the Audi e-tron in 2019.
O’Malley revealed that IIHS crash tests vehicles with EV batteries that have been charged at only 12.5% of a full charge. He explained why: “These batteries have a lot of energy in them, and a thermal runaway accelerates quicker the more power is in the battery itself. If a battery is fully charged and something happened inside it, the thermal runaway would happen really quick. At 12% it still is going to happen with a damaged battery, but it just happens much slower, so that’s why we settled at 12%. That’s kind of a common range across the industry…and based on other labs.”
After it tested the 2021 Volvo and Ford vehicles, IIHS said “evidence is growing that electric vehicles are at least as safe as conventional ones,” granting the Volvo model its highest “top safety pick+” award and the Ford its lower tier “top safety pick” award.
“We can now say with confidence that making the U.S. fleet more environmentally friendly doesn’t require any compromises in terms of safety,” IIHS President David Harkey said in a statement.
O’Malley said, “I would definitely consider an EV [in the future] and I think we all would need to consider one in the next 10 years. We won’t have much of a choice. I would drive one today.”
A bonus to owning an EV is that they are usually significantly heavier than gas-powered vehicles and can better withstand a crash. The XC40 Recharge weighs 4,787 pounds compared with 3,811 pounds for the conventional model, while the Mach-E weighs 4,516 pounds, higher than many conventional SUVs.
IIHS said that injury claims related to drivers and passengers of EV were 40% lower than for identical conventional models over 2011 to 2019.