Gas leak explosions, like the March 12 blast that leveled two five-story buildings in New York City's East Harlem, are commonplace nationwide and are not always due to aging infrastructure. In fact, experts in and out of industry say significant incidents in U.S. gas distribution pipelines occur on average every four to six days, and excavation work is often to blame for pipeline damage, according to the Pipeline & Hazardous Materials Safety Administration (PHMSA).

Photo By Jeffrey Cox/ENR
Investigators are still combing the blast site, where two five-story buildings once stood, for clues.
Photo By Jeffrey Cox/ENR
Side streets off of Park Avenue are used for staging.

While the first of the lawsuits related to the deadly Harlem blast has been filed, the National Transportation Safety Board's (NTSB) investigation is ongoing. The agency says it will consider all and any possible causes, but many industry experts cited in the media blame the explosion — which killed eight and injured more than 60 people — on aging pipeline infrastructure.

On March 18, the agency confirmed suspicions that there was a gas main leak and said that an 8-in. cast iron and plastic main on Park Ave. between 116th and 117th streets failed a recent pressure test at the normal operating pressure. NTSB said the leak was adjacent to 1646 Park Ave., one of the two collapsed buildings. Con Edison, which NTSB has named as a party to the investigation, plans to run a camera probe through water and sewer pipes between those streets.

Workers have removed a 20-ft-long service line segment and a 3-ft-long segment in the basements of both buildings for examination. Pressure testing of the service lines to Park Avenue buildings adjacent to the destroyed buildings is under way.

Investigators plan to examine cut and removed pipe segments as well as a cracked water main pipe in front of 1644 Park Ave., the other collapsed building. NTSB says that, pending fire department recovery work, the leak location will be excavated to expose the gas main pipe for further investigation.

The agency says it will continue to collect gas and water systems operation, maintenance and repair records for the affected area.

Con Edison, which refers calls on the matter to NTSB, says on its website that it last surveyed the blast area on Feb. 28 and found no leaks.

The Harlem blast came the day after the Center for an Urban Future, a Manhattan-based think tank, released a comprehensive report on New York City’s aging infrastructure. The group estimates it would cost $47 billion during the next four to five years to bring the city's infrastructure to a state of good repair.

Upgrades to New York State’s 4,254 miles of gas distribution cast/wrought iron mains — second only to New Jersey with 4,279 — can’t happen soon enough, says Samya Lutz, outreach coordinator at Pipeline Safety Trust, a Bellingham, Wash., advocacy group.

"It's a terrible quandary for the state, but it is something that needs to be replaced," she says.

PHMSA says that while the lineal footage of cast iron pipelines is declining nationwide, there are still incidents involving those that remain. The agency cites, for example, a Jan. 9, 2012, incident in Austin that resulted in one fatality and one injury. A leak originating at a break in a four-in cast iron gas main occurred. The break in the 62-year-old main followed rainfall and extended drought conditions.

New York State has 47,880 miles of gas distribution lines, and last year had 11 significant incidents; 12 injuries and no fatalities, according to PHMSA. That compares with more than 2.1 million miles of gas distribution lines nationwide, with 60 incidents, 39 injuries and eight fatalities in 2013.

PHMSA is working with stakeholders including states and pipeline operators to raise awareness and provide guidance on how to work around existing underground infrastructure, says Damon Hill, a PHMSA spokesman. This includes the cast and wrought iron distribution pipelines that were installed as early as a century ago in certain regions of the country and are especially common in the Northeast.