One Volt battery pack that was being closely monitored following a government crash test caught fire Nov. 24, the safety administration said in a statement. Another recently crash-tested battery emitted smoke and sparks, the statement said.
GM, which was informed of the investigation on Friday, said in a statement that the Volt “is safe and does not present undue risk as part of normal operation or immediately after a severe crash.”
The latest fires are in addition to a battery fire in a crash-tested Volt six months ago.
NHTSA learned of a possible fire risk involving damaged Volt batteries when a fire erupted in a Volt that was being stored in a parking lot of a test facility in Burlington, Wis. The fire was severe enough to cause several other vehicles parked nearby to catch fire as well.
The car had been subjected to a side-impact crash test more than three weeks earlier, on May 12, during which the battery was punctured and its coolant line ruptured.
The more recent tests of three battery packs were designed to replicate the May test. In that test, the Volt was subjected to a simulated side-impact collision into a narrow object such as a tree or a pole, followed by a rollover, the agency said.
The first battery tested didn't catch fire. But a battery test on Nov. 17 initially experienced a temporary temperature increase and, on Nov. 24, caught fire while being monitored. Another battery tested on Nov. 18, which was rotated 180 degrees within hours after the test, began to smoke and emit sparks shortly after the rotation.
The tests were conducted by NHTSA and the Energy and Defense departments at a defense facility near Hampton Roads, Va.
So far, no fires have been reported in Volts involved in roadway crashes, NHTSA said. More than 5,000 of the vehicles have been sold.
It's too soon to tell whether the investigation will lead to a recall of any vehicles or parts but the government will ensure consumers are informed promptly if that occurs, the agency said.
Electric vehicles are critical to President Barack Obama's plans to reduce U.S. dependence on foreign oil. He has called for putting one million of the vehicles on the road by 2015.
The Volt and Nissan's Leaf, with more than 8,000 cars on the road in the U.S., are among the first mass-marketed plug-in electric cars. They went on sale in the 2011 model year. Other automakers are also working on electric vehicles.