The federal investigation into the deadly East Harlem buildings explosion entered a new phase Friday as officials prepared to pressure-test natural gas lines in the area.
Officials said tests done after the Wednesday morning blast found high concentrations of gas in the ground.
At least five of more than 50 test holes dug by Con Edison workers at the scene indicated the presence of 5 percent to 20 percent natural gas in air samples, officials said.
"This further leads to the hypothesis that this may well have been a natural gas leak," said National Transportation Safety Board member Robert Sumwalt.
Sumwalt said there shouldn't be any gas in the samples.
Two days after the thunderous blast that felled two five-story apartment buildings at East 116th Street and Park Avenue, lingering hot spots in the rubble were doused, ending the plume of smoke that had choked the neighborhood.
Authorities yesterday confirmed the deaths of eight people and said all known victims have been accounted for. Seven of the victims have been identified.
Fire Commissioner Salvatore Cassano said 60 percent to 70 percent of the debris pile has been cleared from the site, allowing investigators to get closer to the basements -- where they expect to learn more about how the blast occurred.
Despite round-the-clock work, fire officials indicated it could be two days before investigators can safely gather evidence and conduct leak tests on the gas distribution line that runs along Park Avenue, Sumwalt said.
In the meantime, Con Edison workers, under the supervision of the NTSB, will perform pressure tests on a distribution line along East 116th Street, between Park and Madison avenues.
The tests will tell authorities if that pipe is leaking, Sumwalt said. If not, it can be turned back on so residents who had to evacuate nearby buildings can return.
The main line running along Park is made of 8-inch cast iron with half-inch-thick walls. It was installed in 1887, but age should not matter if the pipe was properly maintained, officials said.
Sumwalt urged people who smelled gas or witnessed the blast to email investigators at witness@NTSB.gov.
John McAvoy, CEO of Con Edison, has said the utility searched its records going back three years and found only two calls about gas problems on the block where the explosion took place, and both of those, in 2011 and 2013, were problems with the customer's equipment.
The tragedy has generated an outpouring of support for the victims and their families.
A half-dozen women gathered Friday morning at the corner of 116th Street and Lexington Avenue and began praying aloud in Spanish.
Former President Bill Clinton, who has an office on 125th Street, dropped by and talked briefly to rescue workers.
Mayor Bill de Blasio announced that the Real Estate Board has arranged for 34 apartments on the East Side "to be available for up to three months . . . and is working with city housing agencies to seek out long-term housing arrangements," officials said.
The city medical examiner's office said autopsies have been conducted on seven of the victims killed in the blast and the deaths have all been ruled "accidental."
While officials don't expect to find any trapped survivors or additional bodies, Cassano said emergency workers are treating the site "like there still could be somebody in there."
The people killed in the explosion have been identified as Griselde Camacho, 45, a Hunter College security officer; Carmen Tanco, 67, a dental hygienist; Andreas Panagopoulos, 43, a musician; Rosaura Hernandez-Barrios, 21, a restaurant cook; her mother, Rosaura Barrios Vazquez, 43; George Ameado, 44, a handyman; and Alexis Salas, 22, a restaurant worker and John Jay College of Criminal Justice student.
The medical examiner's office released the following causes of death: Camacho, blunt impact injuries to head and torso; Ameado, blunt impact injuries to torso and extremities.
Hernandez-Barrios died of smoke inhalation and burns; Barrios Vazquez, blunt force trauma of the head, torso and extremities; Tanco, burns and blunt injuries to the head, torso and extremities; Panagopoulos, blunt injuries to the head, neck and torso; Salas, smoke inhalation and burns.
The city is sheltering 66 people made homeless by the blast, who will be placed in hotels and affordable housing, officials said.
Shortly before De Blasio addressed reporters yesterday outside the Salvation Army shelter at 125th Street and Third Avenue, residents lugging pillows, bags of clothing and other possessions made their way in.
So far, 55 displaced families -- with more than 100 individuals -- have registered with the city for assistance.
"We will stand by them every step of the way," the mayor said. "We will not let them fall."
With Ellen Yan, Matthew Chayes, Anthony M. DeStefano and John Valenti