STEVE INSKEEP, host:
OK. So let's say we took all of the natural gas pipelines in this country -that would be 2.4 million miles of pipeline - and laid them end-to-end. Those pipes would wrap around the Earth almost 100 times. And they're made of many different kinds of materials, some in better shape than others, as NPR's Jeff Brady reports.
JEFF BRADY: Most of the big gas pipelines are in rural areas, but they do pass through cities. In fact, there's one just a few miles from where I live in Denver.
(Soundbite of door opening)
BRADY: Well, there's not much to see here and just about the only indication that this is anything other than an empty field is this yellow pole sticking out of the ground. Just right across the street though, there's houses just a couple hundred feet away. I think I'll head over and talk to some of the folks who live here.
Mr. DWIGHT ANDERSON: My name is Dwight Anderson, and we're in the - northeast Denver, a section called Montbello.
BRADY: Anderson says he was aware of the pipeline but he doesn't think about it much.
Mr. ANDERSON: It's never gave us no problems, or I never smelled gas coming from it or anything like that.
BRADY: The number of serious gas pipeline incidents - the ones that end up in death or injury - actually is on the decline. Still, there are plenty of problems, says Carl Weimar with the watchdog group Pipeline Safety Trust.
Mr. CARL WEIMAR (Pipeline Safety Trust): On average, if you look at all the pipelines in the country, there's a, you know, a significant incident somewhere, oh, about every other day. And someone ends up in the hospital or dead about every nine or 10 days.
BRADY: Weimer says the big transmission pipelines, like the one in San Bruno, don't cause most of the problems. Overall, these pipelines are newer and made of thick steel. It's some of the smaller distribution lines that bring gas close to your home that are a bigger concern. There are many more miles of them and they're made of a wide variety of materials.
Cities first started installing them in the late 1800s, according to Christina Sames with the American Gas Association.
Ms. CHRISTINA SAMES (American Gas Association): Of course, when some of these systems were first put in, they were wood. There's no more wood pipe - at least not that we're finding.
BRADY: 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, some made of plastic, but that process is slow.
Ms. SAMES: The cost of replacing it all at once would be astronomical for the consumer.
BRADY: State utility commissions often have to approve such projects and the rate increases that accompany them. Which leads to one of the tensions pipeline owners face: planning for a failure that's unlikely to happen, but if it does 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. Carl Weimar says the Pipeline and Hazardous Materials Safety Administration has become a more vigorous federal regulator.
Mr. WEIMAR: Ten years ago the agency was fairly atrocious. It was really hard to tell where the industry stopped and the regulators started. It was kind of a revolving door.
BRADY: But today that line is clearer, says Weimar.
And in the wake of the San Bruno explosion, he says it's likely Congress will give pipeline safety plenty of attention this year.
Jeff Brady, NPR News, Denver.