The natural gas pipeline explosion that took down two buildings in East Harlem and killed eight people is raising additional questions about the United States’ reliance on natural gas – or more to the point, whether the infrastructure that carries the fuel source is both safe and adequate.

Similar tragedies have dotted the American landscape in recent years, with the main culprits being older lines that have suffered from corrosion and that have ultimately led to leakage and destruction. In nearly all such cases, the lines had not been inspected for years and they had been made of cast-iron materials that were prevalent more than a century ago – outdated when compared with today’s flexible plastic pipelines.

The increased concerns over pipeline safety are occurring alongside the boom in shale gas, which is increasingly used to fuel electric generation in the United States. That promise is potentially undermined by an aging infrastructure that needs wider tentacles. The network in New York City, for example, consists largely of cast-iron pipelines, just as other northeastern cities depend heavily on those same materials. The ruptured lines that connected to the East Harlem buildings were built in 1887.

“Simply put, too much of the city’s essential infrastructure remains stuck in the 20th Century – a problem for a city positioning itself to compete with other global cities in today’s 21st Century economy,” the Center for Urban Future said – eerily, a day before the Harlem explosions last week.

The New York blast is the latest in a recent string of such incidents. In 2010, a pipeline explosion in Northern California caused nine fatalities and destroyed 38 homes. Subsequently, the National Transportation Safety Board (NTSB) chastised the utility, PG&E Corp., saying that it had no methods in place to detect structural weaknesses in its pipeline. It also said that PG&E did not have shut-off valves to limit the explosion’s severity.

In January 2011, a cast-iron pipe in Philadelphia blew up, killing a utility worker and maiming five others. A similar accident a month later in Allentown, Pa., caused five fatalities.

In December 2012, a gas pipeline explosion occurred just outside of Charleston, W.V., and destroyed several properties, although no one was killed. There, the NTSB concluded that Columbia Gas Transmission had not acted with proper care after finding "external corrosion" in the network and that it had not inspected the pipeline since 1988. Other contributing factors, outlined in an NTSB report last week, included a rocky backfill that contributed to the corrosion and an inadequate alert system that prevented a timely response.

Currently, 2.5 million miles of natural gas pipelines exist in the United States, according to the NTSB. Half of that was installed prior to 1970 and, thus, to older, inferior standards. With the share of natural gas used to fuel power plants expected to keep rising, gas producers forecast that between 29,000 and 62,000 miles of new pipeline is needed over the next 25 years. How can policymakers reconcile that surge of demand with the need for safety?

The age of the underground lines is less important than whether they are getting adequately maintained, said Deborah Hersman, the departing NTSB chair, at a press hearing in Charleston, W.V. a few months ago. Robert Sumwalt, NTSB board member, at a press conference last Friday, reiterated the message saying that proper assessment and risk management are vital.

Federal law requires that pipelines located near population centers – a little under 7 percent of all pipelines – get inspected every seven years. The law doesn't cover other transmission lines - in rural areas, for example. [Editor's note: This paragraph was corrected to make clear that federal law requires inspections of only a portion of the pipeline system.]

With the added focus on natural gas pipeline safety, utilities such as Consolidated Edison, which owns the antiquated system in New York City, and Columbia Gas, say that they are actively working with regulators. ConEd says it is replacing its cast-iron lines with newer plastic, but that it will take two decades and cost $100 million a year.

Most of the accidents that occur do so outside the purview of the operator, according to the pipeline industry. Pipes are ruptured by excavation and other factors, such as fires, while 10 percent of accidents are the result of corrosion, construction, or operation of the lines.

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Nevertheless, a 2011 pipeline safety law is forcing the industry to up its game. New pipelines require the use of remote-control and automatic shut-off valves. It also mandates that operators verify records and reestablish lines’ maximum operating pressures and increases penalties on operators that fail to meet such standards. The law also requires authorities to be notified before any excavation occurs.

The pipeline explosion that rattled New York last week also shook the entire natural gas industry, which must put more safeguards in place to mitigate future accidents. Anything less may topple the foundation that the industry has built to become this country’s energy leader.