IVEL – Federal investigators say external corrosion weakened a natural gas pipeline, leading to a rupture and explosion that destroyed five homes and injured nine people in Floyd County on Monday.

“That’s preliminary,” said Damon Hill, spokesman for the U.S. Department of Transportation’s Office of Pipeline Safety. “We won’t know for sure until we get results back from a metallurgical examination.”

Investigators removed the faulty section of the underground transmission pipeline yesterday. The 4-inch pipeline, made of steel, was constructed some 50 years ago.

Meanwhile, 22 families evacuated from their homes after the explosion were allowed to return to their homes in the Rolling Acres subdivision yesterday afternoon. Some said they were hesitant to return for fear that the explosion may have weakened their dwellings.

John Salisbury said he also is worried the pipeline could explode again when Colorado-based MarkWest Hydrocarbons resumes pumping the natural gas liquids through it. “We just invested $300,000 in our house,” he said. “We’re not going to feel safe enough to live there.”

Kentucky State Police Trooper Scott Hopkins said local building inspectors are available to evaluate the stability of the homes shaken by the explosion.

Smoke was still rising from the smoldering subdivision yesterday morning.

The pipeline carried natural gas liquids to a plant in South Shore in Greenup County, where they’re turned into fuels including butane and propane. The line crosses 81 miles of Eastern Kentucky.

One person burned in the explosion was recovering in a West Virginia hospital yesterday. Rick Conn, a state trooper who helped rescue a woman and 2-year-old child from one of the destroyed homes, was in good condition at Cabell-Huntington Hospital in Huntington, W.Va.

Another resident, James Fulks, was released from University of Kentucky Medical Center yesterday. Seven others were treated for minor injuries after the explosion.

The transmission line that ruptured is owned by Equitable Production Co. but is operated by MarkWest.

Kentucky has 8,242 miles of transmission pipelines crisscrossing the state, often running through residential areas, said Andrew Melny-kovych, spokes-man for the Public Service Commission.

“On top of that, there are literally tens of thousands of miles of distribution pipelines,” he said. “Distribution lines inherently are in residential areas.”

Residents said Rolling Acres was developed in the 1970s, some 20 years after the natural gas line was installed. Salisbury said he didn’t even know a transmission line was near his house.

He and other residents said they want the company to reroute the line around Rolling Acres to eliminate any chance of another explosion.

Hill said the leak occurred under a driveway in the subdivision.

Hopkins said he had no knowledge of any recent work being done on or near the driveway. He said crews had worked on sewer lines in the subdivision about a year and a half ago.

Melnykovych said explosions like the one in Ivel are infrequent. The last one in Kentucky was in November 2003, when a natural-gas transmission line exploded in rural Bath County, shooting flames hundreds of feet into the air. No one was injured, and no property damage was reported.