A natural gas pipeline explosion that killed an Alabama man and injured another and shut down Interstate 20 for hours is being investigated by federal authorities, a spokesman for the company that owns the line said Saturday.

The blast happened just east of Delhi about 1 p.m. Friday and sparked a fire that burned for a couple of hours. About nine hours later, both the eastbound and westbound lanes were reopened, said a news release from the Louisiana State Police.

Officials worked though the night Friday, clearing the scene, which shut down a 4-mile stretch of the interstate. Westbound lanes reopened about 6:45 p.m., and eastbound lanes reopened about 9:40 p.m.

The pipeline is operated by Houston-based Columbia Gulf Transmissions, a subsidiary of energy company NiSource. Columbia Gulf operates about 4,000 miles of pipelines that run from the Gulf Coast to the northeastern United States. The lines pass through 15 states, including Louisiana, Mississippi, Tennessee and Kentucky, before joining other networks near the West Virginia border.

In Warren County, two multistate natural gas pipelines are being constructed, one of which will connect to a hub in Delhi. One of the pipelines is being built by Gulf South Pipeline LLC, the other by Spectra Energy Corp. and CenterPoint Energy Inc.

The Gulf South line is to begin carrying gas Jan. 1, the other in June 2008.

The two pipelines are not affiliated with the NiSource line that erupted Friday.

“This is a tragic situation, and it hurts us too,” said Kelly Merritt, a spokesman for NiSource, Saturday. “We’ve had an excellent safety record over a 54-year period. Until this week, there hadn’t been a fatality involving our company. This is highly unusual, and this is very rare. We work hard every day to keep our pipelines safe, and we take safety very seriously.”

The 30-inch underground pipe, installed in 1954, ruptured near a small bridge that crosses a bayou on Interstate 20 at the Richland-Madison Parish line. A second pipeline near the site was installed in the 1960s, and a third in the early ’70s, said Merritt. All are made of steel.

The other two lines, which were shut off after the blast as a precaution, were not damaged, Merritt said. Gas flow was restored to one Friday evening, he said, and the second was likely to be back in service Saturday night.

“We’ve been hard at it today, working on the investigation, and we’ve brought in independent investigators and structural engineers to look at the damaged pipeline,” Merritt said Saturday.

The U.S. Department of Transportation is part of the investigation, and pieces of the ruptured pipe will be sent off for scientific analysis, Merritt said. “We’ll take as long as necessary to find out what happened.”

The damaged pipeline will not be repaired or restarted until the source of the rupture has been determined. “We need to look at what happened here” to avoid this again, he said.

Following the explosion, automatic equipment kicked in to stop the flow of gas, Merritt said. Other safety features, said the company’s Web site, include around-the-clock monitoring by control centers and routine on-site inspections.

Killed in the explosion was Corbin Fawcett, 47, of Haleyville, Ala. Injured was George McCaleb, 58, of Fayetteville. The two were eastbound on Interstate 20 in a 1985 Chevrolet pickup, driven by Fawcett when the pipeline ruptured.

McCaleb was taken to a hospital Friday with what police called minor injuries. The nearest medical facility is Delhi Hospital, but a person who answered the phone there Saturday night said he could not confirm if McCaleb was a patient.

Sgt. Julie Lewis, a spokesman with the Louisiana State Police, said Friday that evacuations had been ordered, though she didn’t know how many people were affected or for how long. No homes were visible near the scene of the explosion.

Lewis could not be reached Saturday for further details.

Friday’s blast was the second in a month that shut down interstate traffic in Louisiana. An oil well blowout closed a 55-mile stretch of Interstate 10 between Baton Rouge and Lafayette for 10 days from Nov. 10 untol Nov. 25.

In Mississippi, two people were killed in Quitman Nov. 2 when a propane pipeline exploded.