Updated at 5:45 p.m. with latest statement from Atmos.

Atmos Energy refused Friday to say which parts of Dallas have steel pipes like those in the neighborhood where a 12-year-old girl died in an explosion caused by a gas leak.

A company spokeswoman said identifying those neighborhoods would pose a "security risk" under practices Atmos has followed since the Sept. 11 attacks.

The refusal comes as Atmos shut off the gas to the northwest Dallas homes near where Linda Rogers was killed in a blast last week that knocked the home off its foundation and collapsed the roof.

More than 2,800 customers are without gas for up to three weeks while Atmos replaces the lines with more flexible plastic. Steel pipes are common in homes like Linda's that were built in the 1940s and '50s.

Steel pipes have long been known to cause problems. It is unclear why the pipes in the northwest Dallas neighborhood hadn't been replaced before because the company has regularly asked for rate hikes to replace pipelines.

North Texas' clay soil exerts pressure on gas pipelines, as it contracts and expands in wet and dry weather, causing leaks that can lead to deadly explosions if the pipes can't withstand the stress.

Houses in the M Streets, Lakewood, Lake Highlands, along Swiss Avenue, and parts of Oak Cliff and Pleasant Grove may have steel pipes. But old homes don't necessarily mean their pipes are old. They may have been replaced.

The Railroad Commission of Texas, which regulates utility companies, has never ordered a blanket replacement for steel pipelines, said Ramona Nye, a spokeswoman for the commission.

In 2010, The Dallas Morning News reported that Atmos agreed to replace 100,000 aging steel service lines over the next two years to prevent natural gas explosions — work that the company says was completed on time. At one point that year, the commission considered making gas utilities replace all 2.2 million steel service lines with plastic, following several explosions in North Texas.

In 2011, the commission instead adopted a comprehensive pipeline safety rule requiring all Texas natural gas distribution companies to survey their pipeline distribution systems for the greatest potential threats for failure and make plans to replace them.

It was not a mandate to replace all steel pipelines in Texas, but rather a rule directing gas utility companies to survey their lines, determine their greatest potential threats for failure and come up with a plan for replacements. The commission rule stated: "If steel service lines are determined to be the greatest risk in a distribution system, an operator must implement a replacement schedule for these lines."

Any steel segments found with an annualized service line leak rate of 7.5 percent or greater were deemed "Priority 1" and were mandated to be replaced by June 30, 2013.

Lines with leak rates between 5 percent and 7.5 percent per year were deemed Priority 2, and the operator had to remove at least 10 percent of them per year. A segment with an annual leak rate less than 5 percent was deemed Priority 3, and those lines only had to be removed or replaced upon discovery of a leak.

"Unless otherwise approved in an operator's risk-based plan, all replacement programs require a minimum annual replacement of 5 percent of pipelines or facilities posing the greatest risks identified," the rule stated.

Operators were required to submit an implementation plan to the Railroad Commission pipeline safety division by 2011. An Atmos spokeswoman said Friday the company submitted the plan as required to the commission but was not able to immediately provide a copy to The News.

Atmos said the company has replaced 1,700 miles of distribution main and a total of 250,000 steel service lines since the rule was adopted.

A spokeswoman for the commission declined to answer specific questions Friday, saying via email "as part of the RRC's on-going investigation into whether there were any violations of our rules, pipeline safety staff are reviewing all appropriate records to determine compliance."

A National Transportation Safety Board sign on Friday warned people to stay out of the alley behind a home on Espanola Drive where a home exploded last week, killing 12-year-old Linda Rogers. Crews are digging up the surrounding neighborhood to replace natural gas lines in northwest Dallas. (Tom Fox / Staff Photographer)

Federal investigation

A federal inquiry into the explosion has found at least one gas leak at the home that exploded last week as the investigation continues to determine what went wrong.

Atmos Energy has shut off service to the neighborhood, leaving 2,800 customers without gas for as long as three weeks. The company is paying for people to stay in hotels, but residents have not been forced to evacuate as they have been at various times since Linda died Feb. 23. Linda, known by friends and family as Michellita, was buried Friday.

The National Transportation Safety Board said rain has delayed its search for leaks and other evidence. The investigation continued Friday.

The gas line that failed and led to a deadly explosion has been dug up in a neighborhood on Espanola Drive. (National Transportation Safety Board)

"A leak has been found at a service tee connection to 3524 Espanola Drive. This 6-foot long distribution mainline segment has been collected and will be shipped to the NTSB materials laboratory in Washington for examination," the NTSB said in a written statement. "The NTSB plans to conduct further pressure tests on customer gas lines at 3534 Espanola Drive in the next three to four days."

Among the possible causes federal investigators will consider is whether the combination of clay soil and recent rains put too much pressure on old steel pipes and caused leaks. Two nearby homes caught fire in the two days before Michellita's death.

NTSB investigators have interviewed Dallas Fire-Rescue personnel and Atmos employees who responded to the explosion.

It usually takes about 10 days for investigators to finish their on-scene investigation, but an official determination of the cause in major cases can take up to two years.

The failed service tee connection to 3524 Espanola Drive is prepared to be shipped to Washington, D.C. (National Transportation Safety Board)

Residents frustrated

More than 120 crews will work seven days a week around the clock to complete pipe replacements and repairs, Atmos officials said.

Residents whose gas was shut off but want to stay in their homes will be given $250 a day per household, paid five days at a time. Homeowners won't be charged for any repairs. Residents who stay in a hotel paid for by Atmos aren't eligible for the extra money.

Tonya White lives in the 3800 block of Gaspar Drive. She's not under a mandatory evacuation order. But she said that without gas, it's a real challenge for her family to stay in their home.

“We have in-laws, but they’re over an hour away and our children go to school right up the street,” she said. “We’real at the point now where the showering, the cooking is the issue.”

White and several residents expressed frustration Thursday about waiting in line for hours for the money and information. By Friday, Atmos said wait times had been trimmed to 20 minutes at most.

Atmos also said Friday that the company is working with the American Red Cross to improve operations at its two information centers. More than 800 customers have been served and $1.25 million in monetary assistance has been provided so far, Atmos said.

Staff writer Dana Branham contributed to this report.