A defective joint at the connection of a natural gas main and a service tee was among the causes of an explosion that claimed eight lives and injured dozens in the East Harlem neighborhood of New York City last year, according to the National Transportation Safety Board.

Antecedents of the March 12, 2014 explosion (see Daily GPI, March 12, 2014) "had been building for years," NTSB Chairman Christopher Hart said at a hearing in Washington, DC, on Tuesday. "In particular, the inadequate preparation of the service tee resulted in incomplete fusion welding of the service tee to the gas main in 2011, which caused the joint to be defective.

"At least five years prior to that there was a breach in a nearby sewer main, discovered in 2006, which went unrepaired. This neglect resulted in the sagging of the gas main in the vicinity of the service tee."

Those factors "aligned to create the accident, but there were others," Hart said. A New York State Department of Public Service audit program for pipeline operators "does not address all aspects of the state regulations, making it less likely that the defective joint would be detected." In addition, people in the area of the accident failed to report the gas leak on the night of March 11, "calling into question the adequacy of Con Edison's public awareness efforts," and when the leak was reported the following morning, Con Edison failed to notify the New York City Fire Department. And the utility had not installed appropriately located isolation valves, which would have minimized danger to first responders and minimized the delay in recovery operations, Hart said.

Con Edison said that evidence uncovered during the NTSB investigation indicated "that a pre-existing sewer breach beneath the roadway in front of the buildings caused years of street depressions and an undermining of the soil supporting gas and water mains. This undermining resulted in a crack to a water main, as well as a crack in a plastic gas fitting installed in 2011, leading to the explosion. Our investigators believe the separation of a fused section of the plastic gas piping was caused during excavation activities after the explosion."

NTSB has made recommendations to both the city of New York and Con Edison that would help improve gas pipeline safety, "and as the years-long buildup to this accident illustrates, they are long overdue," Hart said.

Con Edison said it is working with the city to better coordinate underground infrastructure projects to help accelerate its gas main replacement program in tandem with the city's water main replacement work, and it has strengthened internal procedures to make sure any lapses in worker re-qualification processes are updated and brought into compliance.

"We are also working with the New York State Public Service Commission in various proceedings initiated by the commission to develop new inspection protocols to identify and remediate potential deficiencies in both new and existing gas pipe plastic fusions; to increase inspections of customer-owned gas service pipes within buildings; and to obtain the resources necessary to significantly expand our gas pipe replacement program," the utility said.