Lynn Celia was in her kitchen talking on the phone when she heard -- and felt -- a blast so loud and powerful she at first thought her roof had collapsed.

She ran outside her home on Mardi Gras Drive in Plum and saw the house of her neighbors, Nino and Tina Pettinato, reduced to a pile of burning debris.

She ran across the street , scanning the burning wreckage to see if anyone was trapped inside.

Out of the corner of her eye, she spotted the Pettinato's 4-year-old daughter, Gianna.

The force of the explosion, strong enough to blow out Ms. Celia's front windows, had catapulted Gianna almost into the next-door neighbors' lawn.

"I just saw her there, sitting on her fanny amongst all this smoke and wood and rubble," said Ms. Celia, 56. "So I just ran over to her, grabbed her and pulled her toward me."

Ms. Celia said she knew Gianna's grandfather, Richard Leith, would come over to babysit her most days.

She started looking for him and shouted his name, but couldn't find him among the debris.

Mr. Leith, 64, of Trafford, was thrown into the street by the blast, Holiday Park Fire Chief Larry Glass said. He was burned over 50 percent of his body and died shortly after 3 p.m. at UPMC Mercy Hospital, according to the Allegheny County Medical Examiner's office.

Gianna was taken to Children's Hospital and treated for a broken leg. Officials declined to release her condition last night, but her injuries were not life-threatening, Plum Police Chief Frank Monaco said.

No other injuries were reported.

Gianna told Ms. Celia she was sitting on the living room couch at the time of the explosion. Her grandfather was in the basement, she said.

"It's a miracle that that little girl is alive," Ms. Celia said.

Public Safety and utility investigators will return today to comb through the debris and charred foundation -- all that remains of the house at 171 Mardi Gras -- in an effort to determine the cause of the blast. Authorities suspect a natural gas leak was to blame but had not confirmed that last night.

Flames were surging at least 30 feet into the air when the first firefighters arrived, said Chief Glass, who described the scene as "chaos.''

"I was out in the kitchen and I heard a sound like I've never heard before. The whole house shook and I didn't know if the roof had fallen in or what,'' said Nancy Wineland, 55, who lives with her mother, Helen Anderson, 86, at 148 Mardi Gras.

"I ran out and just stood there in disbelief,'' she said. "All you saw was smoke and flames."

The explosion also damaged at least 15 other homes in the suburban plan of 1960s-era split-levels and two-story colonials, blasting out windows, cracking walls and tearing chunks from roofs. People reported the impact of the blast in homes and businesses up to a mile away, officials said.

"It was horrendous,'' said Pat Cirocco, 66, who was about to step into the shower at her home at 144 Mardi Gras when the blast nearly shook her off her feet. "I thought my house exploded."

About 80 firefighters from Plum and nearby communities battled the fire for more than four hours as flames continued to flicker in the basement and driveway, fueled by gas that seeped from the ground.

Workers from Dominion Peoples, which provides gas service to the neighborhood, located the house's shut-off valve in the wreckage around 6 p.m.

About 40 homes on Mardi Gras Drive and neighboring streets were evacuated as Dominion Peoples crews went door to door and checked for gas leaks. Authorities quickly opened a temporary shelter at Holiday Park Elementary School.

Red Cross workers said seven families registered for assistance there, but that it appeared everyone displaced by the blast found a place to stay with friends or family. Dominion Peoples offered to pay for a hotel room for any family needing shelter for the night.

Residents who weren't immediately ordered to leave their homes stood shivering in yards or on porches, watching as firefighters worked to douse the blaze. They also marveled at the force of the blast that flung belgian blocks and chunks of dry wall, wood and steel for more than a block and high into treetops, leaving only a blackened hole where a home much like theirs had stood.

Only portions of the home's block foundation remain, creating a partial boundary around piles of wire, fluffy pink insulation and burned wood. Hundreds of strips of siding from that house and others lay tangled on the street and sidewalks, along with nails and shards of glass.

The house on the left side of the destroyed home remained standing, but the side adjacent to the destroyed home was blackened and its windows were blown out. On the right side of the Pettinatos' house, another home's entire side was blown off, exposing its interior.

The explosion also heavily damaged the house behind the Pettinato's home.

Ms. Celia's housemate, Ellie Cravotta, said she'd been in their family room when she heard the explosion and ran outside to find Gianna in the yard outside her house.

"She was in shock," Ms. Cravotta said. "She was just shaking and shaking."

David Heiser, who lives three doors down from the Pettinatos, said he saw Ms. Celia standing in the front lawn near the flames, calling out Mr. Leith's name with Gianna cradled in her arms.

"She was in the yard running around yelling for Rick," said Mr. Heiser, 61. "It was heart-breaking."

Beaten back by the intensifying flames and unable to locate Mr. Leith, Ms. Celia said she retreated from the home.

After checking for injuries, Ms. Celia, a retired nurse, said she waited for an ambulance with Gianna, whose leg was starting to swell. Ms. Celia remembers Gianna repeating, "Where's Pappy?"

"Sweetie, the police are looking for Pappy," Ms. Celia recalled telling the girl.

"I just felt so helpless," she said.

Public safety authorities as well as officials with Dominion Peoples said they suspect natural gas triggered the explosion, but they had not located a leak or determined the cause of the blast last night.

Dominion Peoples spokesman Elmore Lockley said no crews from the utility or its contractors had been working in the neighborhood recently. Crews were last there in September and May to perform routine maintenance, he said.

No residents of the neighborhood reported smelling gas yesterday before the blast, Chief Monaco said.

"Our investigation is still underway and we expect to find more details and facts as we examine our lines," said Ken Johnston, director of gas operations for Dominion Peoples in Pennsylvania and West Virginia. "We'll be there ...until we have this matter resolved."

The neighborhood is served by two Dominion Peoples underground lines, one on each side of the street, that carry gas to lines serving individual houses, he said. Those lines were being checked last night, and gas had been shut off to the line on the side of the street where the explosion occurred, Mr. Johnston said.

Workers will dig down to reveal that buried line and will examine it for potential leaks, he said. But the neighborhood also contains a number of old, plugged gas wells -- some belonging to the utility, some of undetermined ownership, he said.

Those wells also must be located and examined for leaks, Mr. Johnston said.

Residents of the 40 homes that were evacuated remained without gas service last night and the utility was working with the American Red Cross to ensure they had housing, Mr. Lockley said.

"I would like to extend our deepest sympathy to the families involved in this tragedy, and to acknowledge that we'll do everything within our capability to restore service to the area and to have customers back into their homes as soon as possible," Mr. Johnston said.