Federal authorities are investigating the safety and proper handling of lithium-ion automotive batteries after a Chevrolet Volt plug-in hybrid caught fire three weeks after a routine crash test.

The National Highway Traffic Safety Administration has asked General Motors, Nissan, Ford and others about the fire risk posed by li-ion batteries used in EVs and plug-in hybrids, Bloomberg said in an exclusive report. The feds want suggestions for charging and discharging batteries, “including any recommendations for mitigating fire risks.”

The agency said it is not suggesting electric vehicles pose a greater threat  of fire than other vehicles, but their powertrain designs and configurations “require different safety standards and precautions.”

“NHTSA is focused on identifying the best ways to ensure that consumers and emergency responders are aware of any risks they may encounter in electric vehicles in post-crash situations,” the agency said in a statement. “Ultimately, we hope the information we gather will lay the groundwork for detailed guidance for first-responders and tow truck operators for use in their work responding to incidents involving these vehicles.”

The probe — and hand-wringing it is sure to generate — comes as automakers follow the Chevrolet Volt and Nissan Leaf to market. The Obama administration has shown tremendous support for the technology and wants to see 1 million electric vehicles and plug-in hybrids on the road by 2015.

General Motors was quick to defend the Volt. Jim Federico, chief engineer for electric vehicles, insisted, “First and foremost, I want to make this very clear: The Volt is a safe car.”

“We are working cooperatively with NHTSA as it completes its investigation,” he said in a statement, according to Reuters. “However, NHTSA has stated that based on available data, there’s no greater risk of fire with a Volt than a traditional gas-powered car.”

The Volt in question caught fire while parked at a National Highway Traffic Safety Administration testing center in Wisconsin, three weeks after being subjected to a side-impact pole test on May 12, Bloomberg reported. According to Green Car Reports, the test cracked the T-shaped battery pack running down the center of the vehicle.

General Motors spokesman Greg Martin told Bloomberg that GM has outlined safety procedures for dealing with the Volt and its 435-pound, 16-kilowatt-hour battery after an accident. Had those been followed, he said, there wouldn’t have been a fire.

GM spokesman Rob Peterson told the Associated Press the NHTSA failed the drain the battery of energy as outlined in GM’s crash protocol. However, GM had not told the agency about that before the test, Peterson said. Federal regulators typically drain fuel from gasoline-powered cars after crash tests, he said.

General Motors and the NHTSA have replicated the crash on “at least two other vehicles” without the cars catching fire, according to several published reports.

GM has sold approximately 5,000 Volts in the past 11 months. A senior NHTSA official said the agency has received no consumer complaints about fires involving GM or other electric cars, Reuters reported.

The NHTSA has tested the Volt before and given it a five-star safety rating. The Insurance Institute for Highway Safety also has given the car high marks. The Volt’s European cousin, the Opel Ampera, has done well in safety tests by Euro NCAP.

Nissan and Tesla Motors said they have not received any reports of fires involving their vehicles.

Photo of a Chevrolet Volt underground crash testing: Insurance Institute for Highway Safety