Citing fears that terrorists might try to blow up the nation's natural gas pipelines, federal regulators and the industry have made it extremely difficult for homeowners to learn the location of pipelines and any history of inspections and repairs - information that safety advocates say could save lives.
In the wake of a deadly pipeline blast earlier this month in San Bruno, Calif., and serious leaks in Michigan and Illinois, the secrecy surrounding the nation's 2.5-million-mile network of gas transmission lines is facing criticism.
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Many of these tightlipped practices sprang up after the Sept. 11, 2001, attacks, out of fear of another catastrophic attack. Before 9/11, for example, there were no restrictions on who could look at maps of the nation's gas pipelines, but since then, full access to the information has been limited to industry and local, state and federal officials.
The federal government also has asked utilities to remove maps of pipeline infrastructure from their websites.
But lawmakers, safety advocates and independent experts say crucial information is being denied to the public, including emergency workers who must respond when something goes wrong. They say homeowners, for example, have no clue to whether corrosion is eating away the pipeline steel under their feet.
"Large natural gas transmission pipelines are the equivalent of burying dynamite underground," said Paul Blackburn, a public interest lawyer in Vermillion, S.D., who has worked on oil and gas pipeline matters. "The public needs to know lives are being put at risk and property is at risk."
The cause of the San Bruno explosion - which killed four people, injured dozens and destroyed nearly 40 homes - remains under investigation, and it is not clear what problems showed up in prior inspections of the 44-year-old Pacific Gas & Electric transmission line.
What is known is that many in San Bruno first learned of the existence of the pipeline on Sept. 9, when gas leaking from the 30-inch line ignited and sent a fireball shooting hundreds of feet above the San Francisco suburb. Among those previously in the dark was San Bruno Mayor Jim Ruane. He said he is learning "more and more, day by day" about the pipeline, even as he attends funerals for the victims.
It was not the first time a community was caught tragically unaware.
Federal regulators and the industry within the last year were admonished by the National Transportation Safety Board after a propane explosion near Carmichael, Miss., in 2007. A pipeline ruptured because of a failed weld and sent a huge fireball over homes, killing two people and injuring seven.
Key emergency dispatchers had not known about the pipeline; nor were they trained in how to respond, the NTSB said. Also, the victims and others whose houses were destroyed had been left out of public mailings offering pipeline safety tips.
The NTSB said that if local authorities had known of the presence of the pipe, they could have immediately evacuated the area as the propane leaked, and they could have warned people against doing anything that might ignite the cloud of gas.
The Associated Press asked the federal agency that oversees the nation's pipeline network - the Pipeline & Hazardous Materials Safety Administration - for a list or map of the nation's pipelines, including those deemed "high risk" because they are in highly populated areas. But the agency said that information was not available.
The AP sought the same information from the California Public Utilities Commission and the American Petroleum Institute and did not immediately receive a response.
The AP was able to locate numerous gas line maps from the National Pipeline Mapping System, a website created by the U.S. Transportation Department and the industry. But the maps do not say which pipelines are high risk, nor do they include the pipelines' inspection history.
PHMSA spokesman Damon Hill said the agency's public disclosure program is a "work in progress" and more information will be disclosed in the future. For now, he said, a formal request under the Freedom of Information Act must be submitted before full inspection results are disclosed.
"We are trying to be as transparent as possible without giving out information that could be harmful," Hill said.
On Monday, Pacific Gas & Electric Corp. released a list of the utility's 100 riskiest pipeline segments, based on such factors as their design, age, seismic location and potential for corrosion or damage inflicted by others.
CEO Peter Darbee said the section of pipeline that ruptured did not meet the criteria to appear on the list, but he pledged full transparency from now on about the location of what the company considers to be the most dangerous pipe segments.
"We need to begin the process of restoring trust in PG&E and also in PG&E's pipelines," Darbee said. "The best way to accomplish this is to provide information, to be transparent and open in conveying you information."
Richard Kuprewicz, a Redmond, Wash., pipeline engineer and consultant, said his efforts to examine safety threats posed by lines in many communities are often slowed because inspection and repair information is so hard to obtain. He said he had "40 years' experience and it's hard for me to find this stuff out. How about the average homeowner?"
Industry representatives said they have worked to improve their public outreach programs but are reluctant to embrace full disclosure, particularly regarding inspections and repairs.
"In principle we support it, but there's a concern that just sending out raw data can be subject to misinterpretation," said John Erickson, vice president of the American Public Gas Association.
For example, he said, a company that aggressively looks for problems and repairs them could end up looking like a poorly run operation compared with a company that does not maintain its system as rigorously.
As the cleanup in San Bruno continues, some lawmakers are pledging to force more transparency on the industry.
Rep. Jackie Speier, a California Democrat who represents San Bruno and surrounding communities, said she is working on a "right to know" bill that would require utilities to tell residents if a high-pressure gas transmission line runs near or under their property.
"If you had a transmission line in your front yard and if you knew it existed there and you smelled gas, you would be much more certain to call your public utility," she said.