Investigators Tuesday said they discovered a crack in the gas main outside the two buildings destroyed by last week's deadly explosion in East Harlem, an indication that a failure in the main caused the catastrophe.
In a carefully worded statement, the National Transportation Safety Board said the 8-inch cast iron and plastic main under the street "failed the pressure test," which showed that the low-pressure pipe had a leak "adjacent to" 1646 Park Ave., one of the destroyed buildings.
While the NTSB report of a leak in the main will undoubtedly focus more scrutiny on that 127-year-old pipeline, experts said it was still unclear what caused it to crack and when the fracture occurred. A cracked water main pipe was also found in front of one of the buildings.
The NTSB statement didn't address what could have ignited the blast, something FDNY fire marshals are trying to determine.
Eight people died as a result of the explosion and fire last Wednesday at 1644 and 1646 Park Ave., and more than 70 people have been displaced. Tuesday, the FDNY declared the fire under control.
NTSB investigators planned to remove segments of the gas main, as well as pieces of the service lines recovered in the basements of the two buildings, for further forensic tests at the agency's laboratory in Washington.
The NTSB didn't say that the building service lines had shown any evidence of leaks. Tests on service lines to buildings next to the destroyed structures continued "with no significant findings to date," and Con Edison was working to restore gas service to those structures, the agency said in its statement.
A spokesman for Con Edison Tuesday said the utility was continuing its efforts to help displaced families with financial assistance through the Salvation Army and American Red Cross. The spokesman declined to comment on the NTSB statement.
Officials said they also were planning to remove a piece of the cracked water main pipe in front of 1644 Park Ave. for more testing. Last week, law enforcement officials acknowledged that there was a water main leak at the location, but couldn't say whether it occurred before or after the explosion.
For now, the case of the cracked water main is a classic case of what came first, the chicken or the egg, said Robert Malanga, a New Jersey engineer and natural gas expert not involved in the investigation. "Did the crack of the water main come from the explosion, or the thawing and freezing of the ground?" Malanga asked.
Malanga, who has testified as an expert witness in court, said a freeze-thaw cycle can undermine the soil bedding surrounding a main and cause stress on a pipe. Once there is a leaking main, gas will tend to follow underground spaces and lateral service lines and can enter a building, Malanga said. Buildings should have sufficient sealant at the point where a gas service line enters the structure, something that is the building owner's responsibility, Malanga said.