There are 2.4 million miles of natural gas pipelines in the U.S. Laid end to end, that infrastructure would wrap around Earth 96 times.
The big pipelines are mostly in rural areas, but they do pass through cities. In Denver's Montbello neighborhood, there's a large gas pipeline just a few hundred feet from Dwight Anderson's home.
"It never gave us problems," Anderson says. "I never smelled gas coming from it or anything like that. So the pipeline stays buried, and we forget about [it]."
The number of serious gas pipeline incidents — the ones that end in death or injury — is on the decline. Still there are plenty of problems, according to Carl Weimer, executive director of Pipeline Safety Trust.
"On average, if you look at all the pipelines in the country, there's a significant incident — somewhere — about every other day," Weimer says. "And someone ends up in the hospital or dead about every nine or 10 days."
Weimer says the big transmission pipelines — like the one in San Bruno, Calif., that exploded last September — don't cause most of the problems. There are 300,000 miles of them in the U.S. and, overall, they're newer and made of thick steel.
It's some of the smaller distribution lines that bring gas close to homes that are a bigger concern. There are 2.1 million miles of these pipelines, and they're made of a wide variety of materials.
Cities first started installing them in the late 1800s, according to Christina Sames, vice president of operations and engineering at the American Gas Association.
"When some of these systems were first put in, they were wood," Sames says. "There's no more wood pipe — at least not that we're finding."
These days, cast iron pipes are a concern in wetter climates where the pipe doesn't hold up as well. Some utilities are replacing those lines with more durable pipes, made of plastic or steel. But that process is slow.
"The cost of replacing it all at once would be astronomical for the consumer," Sames says.
State utility commissions often have to approve such projects — and the rate increases that accompany them — which leads to one of the significant tensions pipeline owners face: planning for a failure that, though it's unlikely to happen, could be catastrophic.
Questions like how much to spend on maintenance can be tricky when there are shareholders to keep happy. An aggressive regulator can help by looking over a company's shoulder. But the primary federal regulator, the Pipeline and Hazardous Materials Safety Administration, hasn't always had a good reputation.
"Ten years ago the agency was fairly atrocious," says Weimer of the Pipeline Safety Trust. "It was really hard to tell where the industry stopped and the regulator started. It was kind of a revolving door."
But now that line is clearer, Weimer says.
It's likely that pipelines will get extra attention in Congress this year. With the San Bruno explosion still fresh, lawmakers are set to reauthorize the Pipeline Safety Act.
"I think that we need to make sure that we're restoring the confidence of the public in the safety of the transmission pipeline industry," says Donald Santa, president of the Interstate Natural Gas Association of America.
Santa says that could be accomplished by making sure the legislation is seen as strong and credible.
"I think it's also having us commit the resources to pipeline safety," Santa says, "to move us closer to the goal of having no pipeline safety incidents."