UPDATED — The National Transportation Safety Board found that a natural gas explosion that destroyed two apartment buildings in the Harlem section of New York City was caused both by a defective plastic pipe joint that allowed gas to leak from a gas main into the building, and an earlier breach in a sewer line that caused the gas main to sag and overstressed the defective joint.
The explosion on March 12, 2014, killed eight, injured 50 and displaced more than 100 families.
Among the findings released June 9 by the board was that the surfaces of the service tee and the gas main were not adequately prepared before the tee was fusion-welded to the gas main in 2011 by a contractor to Consolidated Edison Co. of New York Inc., resulting in a defective fusion joint.
The board also issued a safety alert regarding the proper cleaning and surface preparation procedures to ensure strong joints in plastic natural-gas pipelines.
In addition, the board found that the New York City Department of Environmental Protection (NYC DEP) had learned of a sewer main breach in front of the apartments on Park Avenue in 2006, but never repaired it. The supporting soil under the gas line and a water main, in front of the five-story buildings, was washed into the sewer through a large hole in the sewer wall.
The sagging gas main led to a crack in the defective service-tee fusion joint, allowing natural gas to escape into the ground and migrate, causing the blast and ensuing fire that destroyed the two buildings.
“We made recommendations to the City of New York, the New York State Public Services Commission, and Con Edison to prevent this from happening again,” NTSB Chairman Christopher Hart said in a news release. “The public's safety would be greatly advanced by these safety improvements, and the public needs to insist on them.”
Tony Radoszewski, executive director of the Plastic Pipe Institute, said in an email that the trade association has been working with regulators and operators to disseminate information about standardized procedures for 50 years.
“While we are not in a position to agree or disagree with the NTSB findings without a detailed review of the complete report, if the cause of the explosion was due to poor fusion, regardless of material, proper training of the installer is the paramount issue,” Radoszewski said. “The Plastics Pipe Institute, through the collaborative efforts of our member companies, publishes specific procedures on fusing plastic pipe and fittings and has worked with ASTM in the development of their national standard practice for heat fusion joining of polyethylene pipe and fittings.”
As of 2013, there are nearly 677,000 miles of plastic gas mains in the United States and more than 46 million plastic service connections from the main line to the meter at houses and businesses, according to PPI.
The gas industry embraced polyethylene pipe decades ago specifically for its corrosion resistance and fused leak-free design, he added, noting that 95 percent of new main lines are made of PE.
“While any explosion and subsequent loss of life and property is a tragedy, this is a very rare occurrence…,” Radoszewski said.
The NTSB investigation also examined the effectiveness of Con Edison's gas odor public awareness program, the adequacy of its gas odor report response, the effectiveness of NYC DEP's sewer integrity program and the effectiveness of federal and state oversight.
“But even if all these recommendations are acted upon, they will not stop every leak,” Hart said. “Don't assume your neighbor reported the gas leak. If you smell gas, first evacuate and move away from the building and then report the leak, either to 911 or to the gas company.”