SAN BRUNO, CALIF. ? An ominous theme has emerged from the wreckage of a deadly pipeline explosion in California: There are thousands of pipes just like it nationwide.

A man walks past the remains of homes damaged from a fire caused by a rupture in a natural gas line in a mostly residential area Monday in San Bruno, Calif. The explosion prompted California regulators to order the utility, Pacific Gas and Electric, to survey all its natural gas lines in the state in hopes of heading off another disaster.

Utilities have been under pressure for years to better inspect and replace aging gas pipes — many of them laid years before the suburbs expanded over them and now are at risk of leaking or erupting.

But the effort has fallen short. Critics say the regulatory system is ripe for problems because the government largely leaves it up to the companies to do inspections, and utilities are reluctant to spend the money necessary to properly fix and replace decrepit pipelines.

“If this was the FAA and air travel we were talking about, I wouldn’t get on a plane,” said Rick Kessler, a former congressional staffer specializing in pipeline safety issues who now works for the Pipeline Safety Trust, an advocacy group based in Bellingham, Wash.

Investigators are still trying to figure out how the pipeline in San Bruno ruptured and ignited a gigantic fireball that torched one home after another in the neighborhood, killing at least four people. Pacific Gas and Electric Co., the pipeline’s owner, said Monday it has set aside up to $100 million to help residents recover.

Old gas lines

Experts say the California disaster epitomizes the risks that communities face with old gas lines. The pipe was more than 50 years old — right around the life expectancy for steel pipes. It was part of a transmission line that in one section had an “unacceptably high” risk of failure. And it was in a densely populated area.

The blast was the latest warning sign in a series of deadly infrastructure failures in recent years, including a bridge collapse in Minneapolis and a steam pipe explosion that tore open a Manhattan street in 2007. The steam pipe that ruptured was more than 80 years old.

The section of pipeline that ruptured was built in 1956, back when the neighborhood contained only a handful of homes. It is a scenario that National Transportation Safety Board vice chairman Christopher Hart has seen play out throughout the nation, as suburbs have expanded.

“That’s an issue we’re going to have to look on a bigger scale — situations in which pipes of some age were put in before the dense population arrived and now the dense population is right over the pipe,” he said.

Thousands of pipelines nationwide fit the same bill, and they frequently experience mishaps. Federal officials have recorded 2,840 significant gas pipeline accidents since 1990, more than a third causing deaths and significant injuries.

“In reality, there is a major pipeline incident every other day in this country,” said Carl Weimer, Pipeline Safety Trust’s executive director. “Luckily, most of them don’t happen in populated areas, but you still see too many failures to think something like this wasn’t going to happen sooner or later.”

Congress passed a law in 2002 that required utilities for the first time to inspect pipelines that run through heavily-populated areas. In the first five years, more than 3,000 problems were identified — a figure Weimer said underscores the precarious pipeline system.

Gaps in system

Even when inspections are done and problems found, Kessler said, there is no requirement for companies to say whether or what kind of repairs were made. And Weimer added industry lobbyists have since pushed to relax that provision of the law so inspections could occur once a decade or once every 15 years.

Other critics complain that the pipeline plans are drafted in secret with little opportunity for the public to provide input about the process.

The Pipeline and Hazardous Materials Safety Administration is the federal regulatory arm that enforces rules for the safe operation of the nation’s pipeline system. Most state public utility agencies have adopted the federal rules and carry out inspections and enforcement.

But the system often relies on the pipeline operators like Pacific Gas & Electric to survey their own gas lines and to decide which pipelines are high-risk.

The American Gas Association disputes the notion that it cuts any corners and says the industry is subjected to stringent state and federal regulations.

“Safety is unequivocally the No. 1 priority for the natural gas transmission and distribution industry and always will be,” spokesman Chris Hogan said. “The industry spends billions each year to ensure the safety and reliability of the natural gas infrastructure.”

The challenge of ensuring pipeline safety is compounded by the sheer enormity of the nation’s natural gas network. The Pipeline and Hazardous Materials Safety Administration says the U.S. has more than 2 million miles of pipelines — enough to circle the earth about 100 times.

The agency has only about 100 federal inspectors nationwide to ensure compliance, meaning there is no guarantee violators will be caught. “When you look at two-and-a-half million miles of pipeline with 100 inspectors, it’s not reassuring,” Weimer said.