MICHIGAN, United States – GENERAL Motors, concerned about the image of its Chevrolet Volt, is offering free loaner vehicles to owners who are worried about the electric cars catching fire.

The move comes after a government safety agency said on Friday that it is investigating fires involving the Volt’s lithium-ion battery packs following crash tests. Thus far, the Volt tests have not raised concerns about the safety of other electric cars, the agency has said.

GM said on Monday that the vehicle is safe. But it will contact owners of the more than 5,000 Volts sold in North America since December 2010 to reassure them. It will also offer loaner cars to ensure that owners are satisfied and confident in their purchase. GM has not put a time limit on how long customers can keep the loaners, but said the offer is not a response to demands from customers.

The National Highway Traffic Safety Administration (NHTSA) said a Volt battery pack that was being monitored caught fire on Thursday, a week after it was hit in a side-impact crash test. The agency said another battery that was crash-tested recently gave off smoke and sparks. The latest fires are in addition to a battery fire at a test facility in Wisconsin back

in June.

The Volt, which can travel about 35 miles (56 kilometers) on electric power before a small gasoline generator kicks in to run the car, has helped Chevrolet’s public image, and GM is eager to protect that good will. The company has promoted the car extensively

as a first step toward independence from foreign oil, and the Volt has helped counter a gas-guzzling image left over from years of GM selling mainly pickup trucks and inefficient sport utility vehicles.

Mary Barra, GM’s senior vice-president of product development, said both fires reported by NHTSA occurred seven days to three weeks after the crash tests, and could have been prevented if the battery charge had been drained as GM has called for in its post-crash procedures.

She said only a few Volts have crashed on public roads. None have caught fire,

nor have the battery packs been compromised.

“We don’t think there’s an immediate fire risk,” said GM North American President Mark Reuss, who addressed the media in a conference call along with Barra. “This is a post-crash activity.”

NHTSA wasn’t aware of the post-crash procedures at the time of the June fire, GM officials have said. In the US, GM is notified of any severe Volt crashes through its OnStar safety system, and it sends a team to the car within a day to drain the battery charge to prevent any fires.

In the Volt’s system, Lithium-ion battery cells, which essentially are a single battery, are assembled into a pack of cells, and coolant is pumped between the cells to keep them from overheating. In the June fire at a test facility in Burlington, Wisconsin, coolant leaked from the battery and crystallised, and that could have been a factor in the fire, GM has said. The fire came three weeks after a side-impact crash test and was severe enough to cause several other vehicles parked nearby to catch fire as well.

Barra said that in all the Volt incidents, the battery cells were not involved in the fires, only the electronics within the battery pack. But she would not be more specific until NHTSA’s investigation is over.

Reuss said GM won’t sell any Volts in other countries until

it makes sure emergency responders, salvage yards and dealers have been trained to discharge the batteries after a severe crash.

The Volt and Nissan’s Leaf, with a total of more than 8,000 cars on the road in the US, 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.

The safety testing hasn’t raised concerns about electric vehicles other than the Volt, but NHTSA is asking manufacturers who have electric cars on the market, or who plan to introduce them, for more detailed information on battery testing. The agency also is asking for the companies’ procedures for discharging and handling batteries, including recommendations for reducing fire risks.

Lithium-ion batteries, which are rechargeable, have been the subject of several recalls of consumer electronics. Millions of laptop batteries made by Sony Corp for Apple Inc, Dell Inc, Lenovo Group Ltd and other PC makers were recalled in 2006 and 2007 after it was discovered that they could overheat and ignite.

The Federal Aviation Administration issued a warning to airlines about the potential for fires in cargo containing lithium-ion and non-rechargeable lithium metal batteries after a United Parcel Service plane crashed near Dubai last year, killing both pilots. The plane, which was on fire, was carrying thousands of lithium batteries.