Fire officials said flames seen rising from the car's top hatch were part of a controlled burn and officials expressed confidence the car was stable, The Sacramento Bee reported.
Firefighters pumped the rail car full of water and aqueous foam Wednesday to try to force out any liquid and propane vapors, Lincoln Fire Chief Dave Whitt said. The flame was lit to burn off residual vapors, he said.
Once water and foam starts to overflow from the top of the car, the car's contents will be inert, Whitt said.
"We feel pretty confident that the water is filling up the tank, pushing out the vapors," Whitt said late Wednesday. "Basically we've got a nice propane fireplace type of thing."
Whitt said the fire could have been caused by an accidental spark but remained unknown pending an investigation.
Nearly 5,000 homes were evacuated Tuesday after the tanker car caught fire, the Bee said.
"It's a blessing to be able to go home," said Ruth Escobar, 33, who stayed in a shelter with her two children.
Fire crews responded Tuesday to 911 emergency calls about flames seen shooting from the top of the full 30,000-gallon propane rail car parked off the Union Pacific main line. One person hospitalized for burns has been released, Whitt said.