It's been a week since a massive natural gas explosion leveled a neighborhood in the San Francisco suburb of San Bruno.
Investigators still don't know why the decades-old pipeline ruptured and burned like a giant torch.
They do know that the incident could have happened anywhere because so many communities are built near aging pipelines.
The fiery explosion claimed four lives and destroyed more than 30 homes.
Residents of the neighborhood have been asking the same question: Why didn't anyone tell us we were living near a natural gas pipeline?
"I had no idea," says Michelle Ashley, a mother of two young children. "It's something you don't think about. You think about the neighborhood, the schools and access to the freeway, but you don't think about what's underneath you."
Ashley's home is across the street from the ruptured pipeline. Her home is still standing but everything inside is smoke damaged and has been declared a total loss.
"If I did know, it might not have mattered," Ashley says. "I've never heard of a fire, you know, something so devastating caused by this."
But Carl Weimer knows a lot about the underground potential for a catastrophe. He directs the Pipeline Safety Trust, an advocacy group based in Bellingham, Wash.
"There's 2.5 million miles of pipelines all over this country, and on average there's a significant pipeline incident every other day," Weimer adds.
Weimer believes the San Bruno incident was bound to happen.
"The pipeline companies have worked real hard to keep their pipelines out in the middle of nowhere," Weimer says. "Unfortunately, our communities have grown over the past 40, 50, 60 years when the pipelines were put in. Often times, we're now putting housing developments or businesses right near or on top of pipelines."
The San Bruno pipeline that ruptured was 50 years old, and across the country, there are thousands more like it. Since 1990, federal officials have reported more than 2,800 significant gas pipeline accidents.
The nation's pipeline network is in private hands but subject to federal and state inspectors who are spread too thin.
"Part of the way the regulations are set up is that they need to come up with a regime to do the inspection to make sure their pipelines are safe," Weimer says. "Then the government looks over their shoulders to make sure they are doing it at least to the minimum regulations. Some of the companies go way beyond what they are required to do, and other companies are skirting by doing the bare minimum."
After last week's tragedy, Pacific Gas and Electric Co., the owner of the ruptured gas line, found its operations under increased scrutiny.
The industry watchdog group The Utility Reform Network, or TURN, released documents showing that three years ago PG&E asked for and received a rate hike to replace a portion of the same pipe that ruptured.
That portion was 2 miles north of the explosion, but PG&E never did the job, says Mindy Spatt of TURN.
"We're not saying that the explosion could have been avoided had it been fixed, but it couldn't have hurt to look at a section of pipe that close by," Spatt says.
In a statement posted on its website, PG&E said it is constantly prioritizing its projects, and that it is committed to the safety of its gas transmission system.
At the same time, the Obama administration has proposed new laws to increase the maximum fines for major safety violations that lead to death or injury. Plus, it wants to hire more inspectors.