DETROIT (AP) — The liquid solution that cools the Chevrolet Volt’s batteries is the likely cause of fires that broke out inside the electric car after government crash tests, a person briefed on the matter said.

Engineers at General Motors Co., which makes the much-celebrated car, are working on structural changes to strengthen the car’s T-shaped battery pack, the person said. They are also looking at ways to bolster the Volt’s body to make it more resistant to side-impact crashes.

The coolant did not catch fire, but crystallized and created an electrical short that apparently sparked the fires, said the person, who asked not to be identified because the findings are not final.

On Nov. 25, the National Highway Traffic Safety Administration opened an investigation into Volt battery fires, which occurred from seven days to three weeks after crash tests by the agency. NHTSA spokeswoman Lynda Tran would not comment on the investigation Tuesday evening.

The chemical reaction that stores and discharges energy from the battery is not the culprit, and engineers believe that if they can stop the coolant from leaking, they can stop the fires, the person said.

Also Tuesday, Transportation Secretary Ray LaHood, whose agency includes NHTSA, told reporters that the Volt is safe to drive even though the government is investigating the fires. NHTSA is interested in setting up procedures for safely dealing with electric cars after crashes.

Transportation officials launched their investigation after a Volt that was damaged in a crash test caught fire at a test facility in Wisconsin in June. The blaze occurred three weeks after a side-impact crash test, and the car had been left out in the elements after the test. Investigators then tried to duplicate the fires by similarly damaging two Volt battery packs. Both set off fires.

GM has said that no Volts have caught fire in real-world crashes. The company is notified of any crashes through its OnStar safety system, and it dispatches a team to drain the batteries within 48 hours. GM said NHTSA didn’t drain the battery packs of energy after the tests, but the automaker acknowledged that it hadn’t told the agency of its procedures back in June when the first fire occurred.

Last week, GM CEO Dan Akerson told The Associated Press that in order to keep its customers happy, GM will buy back Volts from any owners who are afraid the cars will catch fire. He maintains that the car is safe and the fires occurred long after a crash and only when the batteries remained charged.

So far, GM said it has bought back about two dozen of the roughly 6,000 Volts now on U.S. roads. The company, clearly concerned about the image of its high-profile new technology, also offered loaner cars to Volt owners until it solves the fire problem. Akerson said he wants to fix the problem and make it right for customers.

Still, the fires could raise questions for potential electric car buyers just as the cars are hitting the market in greater numbers.

In the interview, Akerson said the coolant was among several causes that were under investigation, including circuit boards, the packing of the battery cells and the mixture of the coolant made of glycol, an alcohol compound.

“We’re not the only car company that has liquid-cooled batteries out there,” Akerson said. “There are many.”

He said it’s important for the entire auto industry and the future of electric cars to come up with procedures that work for all battery-powered vehicles. He said Lexus, Toyota Motor Corp.’s luxury brand, had quality problems when it was first introduced, but the company called all the cars back and fixed them, and Lexus went on to wild success. GM expects to follow a similar plan with the Volt batteries, he said.

“I think it behooves everyone including General Motors and all of our competition, but more importantly our customers, that we get it right,” Akerson said.

The Volt’s 400-pound (180-kilogram) battery pack is made up of individual cells that store power and a large case with channels that route coolant around the cells to keep them from overheating.

The Volt can go about 35 miles (56 kilometers) on battery power before a small gasoline-powered generator kicks in to keep the car running. The car can be recharged with a standard home electrical outlet.

The Nissan Leaf, a fully electric car and the Volt’s main competitor, has not had any similar fires after crash tests or real-world crashes, Nissan said. The Leaf battery is cooled by air rather than liquid.