The National Transportation Safety Board (NTSB) has announced that a natural gas explosion that destroyed two five-story buildings in the East Harlem section of New York City was caused both by a defective 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 overstress the defective joint.

The explosion on March 12, 2014, killed eight, injured 50 and displaced more than 100 families.

Among the findings 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 Company 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.

City knew about it for nine years

The Board also found that the New York City Department of Environmental Protection (NYC DEP) had learned of a sewer main breach in front of the building on Park Avenue in 2006, but had never repaired it. The supporting soil under the gas line and a water main, in front of the 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 into 1644 Park Avenue.

Public "needs to insist"

“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,” said NTSB Chairman Christopher A. Hart. “The public’s safety would be greatly advanced by these safety improvements, and the public needs to insist on them.”

The 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.

If you smell gas...

“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.”

The link to the safety alert is here: http://www.ntsb.gov/safety/safety-alerts/Documents/SA_047.pdf

The link to the probable cause and recommendations is here: http://www.ntsb.gov/news/events/Documents/2015_Manhattan_BMG_DCA14MP002_Abstract.pdf