A thunderous gas explosion devastated a rowhouse neighborhood, killing five people, and suspicion fell on an 83-year-old cast-iron gas main. The fiery blast was the latest natural-gas disaster to raise questions about the safety of the nation's aging, 2.5-million-mile network of gas and liquid pipelines.

The explosion, which flattened a pair of rowhouses and set fire to a block of homes late Wednesday night, occurred in an area where the underground gas main lacked shut-off valves. It took utility workers five hours of toil in the freezing cold to punch through ice, asphalt and concrete and seal the 12-inch main with foam, finally cutting off the flow of gas that fed the raging flames.

Dorothy Yanett, 65, said she was in her living room with her husband awaiting the evening news when she heard a series of booms.

"Everything falling and crashing, glass, just a nightmare," said. She found glass in the shoes she was going to put to leave the house. "There was no odor, there was no smell. Then it was like all hell broke loose."

Joe Swope, a spokesman for Reading-based UGI Utilities Inc., said that a routine leak-detection test in that area had come up clean on Tuesday, and that there had been no calls about gas odors before the disaster.

Lehigh County Coroner Scott Grim said four bodies had been recovered — a 4-month-old boy, a 16-year-old girl, a 69-year-old woman and a 79-year-old man — and cadaver dogs searched for the fifth person known to be dead. Their names were not immediately released.

Forty-seven homes were damaged, and eight of them appeared to be a total loss, said Allentown Fire Chief Robert Scheirer.

The exact spot of the explosion and what triggered it were under investigation.

"The investigation will look at the 12-inch main, but will also look at service lines that feed gas into the nearby homes and businesses, as well as potential causes inside the home," Scheirer said. "Until that investigation is complete, it's premature to conclude exactly where the leak took place."

Investigators planned to send cameras through the main to look for cracks, and perform air pressure tests on the service lines.

Last September, a 44-year-old gas transmission line ruptured in San Bruno, Calif., killing eight people, injuring dozens and leaving 55 homes inhabitable. Investigators said the pipe had numerous flawed welds. And in Philadelphia last month, a gas main explosion sent a 50-foot fireball into the sky, killing a utility worker, injuring six people and forcing dozens from their homes. Fire officials are investigating.

Past pipeline explosions have been blamed on such factors as corrosion or damage done by heavy construction equipment.

Rick Kessler, worked on pipeline safety issues for many years as a Democratic congressional aide, said that cast-iron pipe is a vestige of an earlier era and that the federal Pipeline Safety Improvement Act of 2002 envisions its replacement with safer materials, such as steel. He said Pennsylvania may have the most cast-iron gas lines in use.

"Think about the things in your daily life that are made of cast iron, besides a frying pan," said Kessler, now a lobbyist and vice president of the Pipeline Safety Trust, a watchdog group. "We should always be concerned when we have pipes dating back a century, made of materials that may have been state-of-the-art at the time, and really aren't."

Swope said there was no history of leaks in the immediate area of the Allentown explosion. Asked about any plans to replace the main, the utility spokesman said that the section had been deemed safe and reliable. He also said there had been no recent reports of construction in the neighborhood.

As for the possibility that the freezing weather caused a pipe to rupture, Swope said: "In the winter, there's always the concern about the freezing-thawing cycle, but seeing that we just ran the leak survey less than 48 hours before the incident, that doesn't appear to be a cause."

The blaze was too hot to allow workers to go to the curb or a home to cut off the gas, so they had to go into the street to plug up the main, according to the fire chief. Swope said shut-off valves are not considered feasible for that type of main construction, which dates to 1928.

An Associated Press investigation published Saturday found that many pipelines around the country are not equipped with remotely operated or automatic shut-off valves that can quickly stop the flow of gas in an accident, even though federal safety officials have recommended such devices to industry and regulators for decades.

Pennsylvania Public Utility Commission spokeswoman Jennifer Kocher said age is not the only consideration in deciding when to replace gas lines. Other factors include the number of leaks per mile, how the soil's composition could affect the pipe, whether it is located in a densely populated area, the amount of pressure and the size of the line. The gas main in that area was under comparatively low pressure, she said.

The Morning Call newspaper reported that the residents of a rowhouse at the center of the blast were Beatrice and William Hall, according to their daughter-in-law, Michelle Hall. Yanett, one of their neighbors, called the Halls "a beautiful couple" and "just lovely people" who were active in the Methodist church and a local food bank.

Antonio Arroyo said he and his wife fled their home with only the clothes on their backs. Their home was considered a total loss.

"I thought we were under attack," he said in a shelter with about 250 other evacuees a few hours after the explosion.

On Thursday, backhoes dug into the rubble in the devastated neighborhood and plywood covered blown-out windows of a church.

"I was reading a book in the living room and it felt like a giant kicked the house. It all shook. Everything shook," said Tricia Aleski, who lives a few blocks away. "I checked the stove and everything, make sure everything's off."

Jason Soke was watching college basketball when the explosion rattled his windows. He went to the third floor and looked out and saw flames and smoke.

"Your senses kind of get stunned," he said. "It puts you on edge."