Firefighters took a bold step Wednesday to drain a burning propane tanker and prevent the rail car from blowing up as thousands of people were forced from their homes for a second day.

Officials decided to take the step after consulting with members of a national response team from Houston, who were flown in overnight to offer advice to authorities in the Sacramento suburb of Lincoln.

Fire officials initially said the blaze could continue for 21 days, but Lincoln Fire Chief Dave Whitt determined that scenario was unacceptable.

Between 4,000 and 5,000 homes in the city of 40,000 people were evacuated, and more than 6,000 students were missing their first days of classes, with district schools ordered closed until Monday.

Whitt said firefighters now hope to have the blaze under control within 24 to 48 hours.

Officials are trying to head off a potentially catastrophic failure of the 29,000-gallon tank. A buildup of heat could lead to an explosion that Whitt compared to a "small thermal nuclear bomb" that produces a fireball several hundred yards wide.

An explosion also could throw metal shards up to a mile away. Officials ordered mandatory evacuations within a one-mile radius.

Whitt said firefighters have been successful in keeping the tanker cool since it caught fire Tuesday, but he worried that it was showing signs of melting.

"Quite frankly, we are very lucky," he said. "We were really able to put a dent in the progression of the fire."

The procedure to drain the rail car of propane, called a "hot tap," will begin later Wednesday. The tanker will remain in place as a fire crew cuts the outer layer of the tanker and welds a pipe to the side. Steam will then be pushed inside, forcing out the propane and funneling it into a freshly dug basin, where it will be ignited and allowed to burn itself out. The burning process is expected to take up to eight hours and produce black smoke.

Jeff Carman, assistant chief for the fire department in nearby Roseville, said workers hope to start the flames at 5 p.m., meaning the fire could burn until 1 a.m. The city said the mandatory evacuation will remain in place at least through Thursday.

"We hope by the time you wake up in the morning that the entire situation will be resolved," Carman said.

It was unclear how the tanker caught fire. It was burning at the Northern Propane Energy yard in Lincoln, about 30 miles northeast of the state capital in Northern California. It was surrounded by trucks, other rail cars and storage tanks containing at least 170,000 gallons of additional propane that Whitt said were at risk as the fire burned. A gas pipeline also runs through the area.

One worker at the rail yard was injured in the initial fire and suffered flash burns but has been released from a hospital.

A similar fire in 1973 in the Arizona town of Kingman killed 11 firefighters and a gas company worker when a rail car carrying a propane tank exploded. The resulting fireball injured more than 100 others and showered the surrounding area with shrapnel. The propane tanker flew a quarter of a mile and its impact dug a crater 10 feet deep.

Extinguishing the fire near Sacramento would be welcome news to the thousands of residents forced to flee their homes. The American Red Cross said 270 people have taken shelter in three evacuation centers.

Leslie Reyes and her husband, a city maintenance worker, spent the night in their van outside the Lincoln Community Center, one of the three shelters set up for evacuees. Her oldest son slept outside next to the van while three other children were placed with family and friends.

She said they chose to stay outside because they were not allowed to bring in their 2 1/2-year-old toy rat terrier.

Reyes, 35, said she got a call at home Tuesday from her husband to evacuate. A short time later, an officer came to evacuate their street.

"At that point, I told my kids grab your memorables, pictures, things that are near and dear to your heart," Reyes said.

She said she appreciates the precaution despite the inconvenience. Reyes said she plans to relocate her family to her mother's in Antelope, about 15 miles away.

"Of course I would rather go home but it's better to be safe," Reyes said.

Roza Calderon, who lives with her family about a block away from the propane yard where the tanker was burning, described flames as high as utility lines before she evacuated.

"It was a big flame. It was getting worse," she said.

The 26-year-old accountant said she was staying with her husband, daughter and mother at a hotel in Sacramento.

At another shelter, the Kilaga Springs Lodge at a nearby Sun City community, volunteers set out 20 cots but had to add more as evacuees streamed in through the night.

One evacuee at the center, 21-year-old Richard Reyes, said he was hoping to be allowed back to his house soon.

"I guess we began to realize the situation was rapidly deteriorating when they had to call in a team from Texas. They called them super firefighters who fight petroleum fires," said the student and part-time mechanic.

Highway 65, a major commuter thoroughfare between Sacramento and Lincoln, remained closed near the blaze.

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Associated Press writers Sheila V Kumar in Sacramento and Michelle Price in Phoenix contributed to this report.