PORT ALLEN — Henry Williams made it out of his burning house with his girlfriend and her young granddaughter early Friday, but the 74-year-old perished when he ran back inside to try to rescue the 10-year-old boy he called his grandson, authorities said.

Investigators believe the fire that killed Williams and Trevor Baker, a student at Chamberlain Elementary, erupted around a mounted, natural gas space heater in the living room. They believe it spread so quickly because a plastic bottle filled with lamp oil had been sitting on top of it.

Williams’ girlfriend, Carolyn Baker, 55, and her 9-year-old granddaughter managed to escape the fire, which started around 6 a.m. Friday. They sustained only minor burns and were released from the Baton Rouge Burn Unit after treatment for minor burn injuries, according to Brant Thompson, chief deputy with the State Fire Marshal.

Williams also made it out of the home briefly with Carolyn Baker and the girl, Thompson said, but died when he went back into the burning home to save Trevor, who had become trapped inside.

"They heard him yelling out, 'PawPaw! PawPaw, help me!'" Thompson said. "Mr. Williams then re-entered the house, but obviously his rescue attempt was unsuccessful … This is just a tragic situation."

State Fire Marshal Butch Browning said at the scene there were smoke detectors in the two-bedroom wooden house, but they appeared to not be working.

"We had a fast-moving fire in an old home constructed of unprotected wood," Browning said.

The two children were Baker's grandchildren and appeared to be living with the couple. They considered Williams their grandfather, Thompson said. He said their mother lives in Baton Rouge.

Baker told investigators that Williams lit the gas heater that morning because there was a chill in the house when the couple woke up Friday.

At the time, Baker was in the adjacent bedroom where her two grandchildren were asleep. She told investigators she was getting ready to wake them up for school that day.

Shortly after Williams lit the heater and went to the back of the home, Baker told investigators, she heard the sound of crackling fire coming from the living room and then saw flames reaching into the bedroom as the fire quickly spread over the front portion of the small home.

"She immediately began to alert everyone to the fire," Thompson said.

When Baker opened a door in the bedroom leading out to the front porch, the fire erupted further. Baker and her granddaughter were burned by the flames that spread into the doorway as they ran outside, Thompson said.

Instead of following the rest of his family, Trevor Baker turned and ran in the opposite direction, toward the back of the home, Thompson said.

It took a few moments before the couple realized he hadn't made it out with them.

Thompson said the home had a rear exit, but it was blocked with equipment and tires being stored on the inside and tools and large lawn equipment on the outside.

Williams and the boy were later found near each other in the bathroom at the back of the house. Investigators said they believe they were overcome with smoke, although the exact cause of death had not been determined as of Friday afternoon.

Tony Paul, a longtime friend and neighbor of the couple, said he was jolted out of his sleep Friday morning by a call saying that his friend's house was on fire.

"Flames were sky high; smoke was everywhere," Paul said. "It was just a terrible thing to see. He really loved those kids. He would take them everywhere with him."

Parish firefighters and the State Fire Marshal's Office spent much of the day digging through charred remains of the family's home to determine if their theories about what caused the fire are right, and to learn more about why it spread so quickly.

Baker told investigators she had walked past the heater the previous night and considered moving the bottle of lamp oil sitting on top but decided not to since temperatures weren't expected to drop in the next few days.

"Any type of heating source can pose a danger," Thompson said. "Little Trevor's response to the fire was right: flee. Had the rear exit to the home not been blocked, they might have been able to escape."

As of mid-morning on Friday, a brick chimney was all that was left standing amid the smoldering ruins of the small house where the tragedy unfolded.

Follow Terry Jones on Twitter, @tjonesreporter.