U.S. natural gas pipeline network
Department of Energy / msnbc.com
This map shows the network of major U.S. natural gas pipelines in 2009
By M. Alex Johnson Reporter
msnbc.com
updated 9/10/2010 5:02:58 PM ET 2010-09-10T21:02:58

Natural gas mains made of steel, like the one that apparently failed in Thursday’s deadly California explosion, are considered especially susceptible to corrosion and leaking, leading regulators in some states to consider replacing them.

Pacific Gas and Electric Co., which serves the San Francisco Bay Area, said Friday that it had isolated a damaged section of a 30-inch steel pipeline in San Bruno after the blast, which killed at least four people, injured 52 others, destroyed 38 homes and set off a fire that charred 15 acres.

In general, gas pipelines are safer than ever: “Distribution incidents” like leaks, fires and explosions have declined sharply since 1970, when many utilities began switching over to plastic pipes, which are less vulnerable to corrosion, according to the Pipeline and Hazardous Materials Safety Administration. Deaths in such incidents have declined in turn, from 246 in the 1970s to 120 in the 2000s.

But while the majority of natural gas pipes are plastic, about 60 percent of the nation’s 475,000 miles of larger gas mains — those wider than 16 inches in diameter — are steel, according to the Natural Gas Supply Association. That’s because steel pipes can better withstand the pressurization used to move gas efficiently through large pipes.

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That strength doesn’t necessarily translate to safety — federal figures show that steel pipes are implicated in more natural gas incidents than those made of plastic materials.

Through Aug. 11 — the last date for which data are available — the Pipeline and Hazardous Materials Safety Administration recorded 57 such incidents this year, 21 of them involving steel pipes and 11 of them plastic pipes. Most of the other incidents also involved metal pipes, usually aluminum or cast iron.

If you own a gas grill, you probably already deal with the main vulnerabilities of steel pipes. Steel corrodes, and because it’s rigid, it can crack under stress. As older steel gas mains have started giving way, explosions — some of them deadly — have led regulators in several states to reconsider whether they’re the best option.

Atmos Energy Corp., the second-largest natural gas distributor in the country, with operations in 12 states, agreed last month to replace 100,000 of the most vulnerable steel pipelines in its North Texas territories by late 2012. The agreement follows years of investigations by Dallas TV station WFAA into explosions involving steel pipes or steel couplings, like one in January, when leaking gas exploded in a home in Irving, killing the owner and seriously injuring his wife.

U.S. Department of Transportation’s Office of Pipeline Safety / msnbc.com

All told, regulators have identified at least six major explosions since 2006 involving Atmos steel pipelines in Texas, prompting the Texas Railroad Commission, which regulates natural gas pipelines, to study the feasibility of replacing all 525,000 steel service lines across the state.

“Experience has revealed that [steel] is the most prone to leak, so it all needs to come out,” said Geoffrey Gay, a lawyer representing several Texas towns in negotiations with Atmos and the Railroad Commission. “Obviously, my clients are always worried about the health and safety of their citizens.”

Regulators in other states are also starting to crack down.

In Washington, Puget Sound Energy Corp. has until the end of the year to replace about 9,000 older steel natural gas lines in the western part of the state. The deadline was set as part of a settlement with regulators after an investigation of an explosion that killed a 68-year-old woman at her home in Bellevue, a suburb of Seattle, in 2004.

And in Arizona, regulators include a notice in monthly bills sent by Southwest Gas Corp., which serves nearly 2 million natural gas customers in the state and in California and Nevada. The notice warns that “buried steel gas lines are subject to the effects of corrosion if they are not maintained, which could result in leakage,” and says it’s the customer’s responsibility to monitor the lines “to identify these potential problems before they become hazardous.”

It’s not yet known whether the steel composition of the pipe was a factor in Thursday’s blast, but PG&E said it would “take accountability” if it was at fault. The National Transportation Safety Board sent a four-member team to investigate.

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Photos: Massive fire in San Bruno

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  1. Emergency workers sift through rubble of a burned down home on Sunday, three days after the natural gas pipeline explosion. (Tony Avelar / AP) Back to slideshow navigation
  2. Search and rescue teams escort a cadaver dog through a destroyed San Bruno neighborhood on Sunday. (Josh Edelson / EPA) Back to slideshow navigation
  3. An unidentified man inspects the roof of a house labeled with a 'green card,' indicating that it is undamaged. (Josh Edelson / EPA) Back to slideshow navigation
  4. Julie Frechette, left, comforts neighbor Janel Costanzo shortly after the two returned to their fire-ravaged neighborhood on Sunday. Police allowed some residents home for the first time since Thursday night's gas line rupture. Frechette and Costanzo, who live on Glenview Drive, suffered minor damage to their houses. (Noah Berger / AP) Back to slideshow navigation
  5. Hundreds of displaced San Bruno residents jammed a town hall meeting at St. Robert's Catholic Church in San Bruno on Saturday. (Tony Avelar / AP) Back to slideshow navigation
  6. The remains of burned vehicles and homes are seen Saturday near the site of a natural gas explosion. (Noah Berger / Pool via Reuters) Back to slideshow navigation
  7. A wrecked gas pipe lies on the street as investigators gather at the scene on Saturday. (Stephen Lam / Reuters) Back to slideshow navigation
  8. The sun rises on Friday to reveal rows of chimneys where homes once stood. (Peter Dasilva / EPA) Back to slideshow navigation
  9. The explosion left this crater, which by Friday morning had filled with water. (Jeff Chiu / AP) Back to slideshow navigation
  10. Homes sit destroyed or damaged by the fire, which spread from the explosion that produced the crater near top left. (Justin Sullivan / Getty Images) Back to slideshow navigation
  11. A for sale sign is shown in front of three San Bruno homes that were destroyed in the explosion. (Paul Sakuma / AP) Back to slideshow navigation
  12. A massive fire roars through the mostly residential neighborhood of San Bruno on Thursday. (Jeff Chiu / AP) Back to slideshow navigation
  13. Cars were among the possessions destroyed by the fire that followed the explosion. (Paul Sakuma / AP) Back to slideshow navigation
  14. A helicopter drops water on the huge blaze. (Paul Sakuma / AP) Back to slideshow navigation
  15. Firefighters battle house fires Thursday night. In all, 38 homes were destroyed. (Peter Dasilva / EPA) Back to slideshow navigation
  16. A woman is treated after the explosion. (Mike Adaskaveg / AP) Back to slideshow navigation
  17. Evacuees check in with officials in San Bruno. (Jeff Chiu / AP) Back to slideshow navigation
  18. Judy and Frank Serresseque move their cats and a few belongings after they were evacuated following the explosion. (Mike Adaskaveg / AP) Back to slideshow navigation
  19. A video frame grab from KNTV shows part of the fire. (NBC News) Back to slideshow navigation
  20. San Francisco firefighters monitor the flames. (Justin Sullivan / Getty Images) Back to slideshow navigation
  21. A law enforcement official runs toward the massive San Bruno fire. (Justin Sullivan / Getty Images) Back to slideshow navigation
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Video: San Bruno mayor expects more fatalities

  1. Closed captioning of: San Bruno mayor expects more fatalities

    >> latest on the investigation into this disaster from jim ruwane, the mayor of san bruno . mr. mayor, good morning to you.

    >> good morning to you.

    >> most importantly, what's the latest? have you accounted for everybody? i know they've been going street to street. are there still some residents unaccounted for?

    >> we don't know the full count and we won't know until some time tomorrow morning or later this morning, actually, when the sun comes up. late last evening, it was way too hot and too dangerous for the firefighters and the first responders to get into that neighborhood and actually assess the total amount of damage, but we do expect a number of more fatalities.

    >> still the investigation goes on as to what exactly caused this. i know there is some kind of a ruptured transmission line there, but we don't know if that's the exact cause. but look at the numbers here. we have one fatality, 50 homes destroyed, 120 damaged. you've lived in that town for i think over 30 years. what's going to happen to that community?

    >> hard to say right now. we're right in the throes of taking care of the people that we had to evacuate, making sure that they have accounted for all of their family members, getting them assistance, getting them aid, setting up hotlines, doing all the things we have to do to assist them when the sun comes up later this morning. it's a very difficult procedure, and the first response from this whole county as well as san francisco has been absolutely incredible.

    >> well, as i said to mr. pellegrini, mr. mayor, our thoughts and prayers are with all the people in san bruno .

    >> i appreciate that. and as i told the first responders earlier today and earlier at a news conference, for all who are listening, say a special prayer for those people today . thank you.

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