The East Harlem site where two buildings collapsed after a suspected gas leak is still to dangerous for investigators to step in to.
The National Transportation Safety Board said late Thursday that the agency has been unable to trace the source of the gas leak that may have factored into the blaze on Wednesday that killed seven and injured dozens.
Still, agency authorities said they are operating under the assumption that a national gas leak that led to the explosion.
"Our goal for being here is to find out what happened so that none has to tho through this again," NTSB Board Member Robert Sumwaltsaid. "And that's our commitment."
He called the ongoing operations as a rescue and recovery effort, and that NTSB would soon develop a timeline of events based on 311 and 911 records, as well as interviews with witnesses, first responders and those injured by the blast.
However, the New York City Fire Department is still pouring water on the buildings' smoldering remains.
"It's not safe for our investigators to there," Sumwalt told reporters Thursday. "We're not going to go in until the FDNY declares it safe."
Asked about the utility lines that might have led to the explosion, Sumwalt said that the preliminaryinvestigation found no obvious damage or leaks to the low-pressure gaspipe under the buildings.
Investigators will have to run pressure tests on both the main gas line and the smaller service lines that connect to the buildings. Meanwhile, they're waiting to hear back from Con Edison on a number of details about the pipes that ran to the building, includingits diameter, age and typical operating pressure.
And despite early reports that a water main break may have somehow factored into the blast, Sumwalt warned there is no conclusive evidence to say so.
"We don't know at this point, but we will determine it — whether the water main break was the result of the explosion or may have somehow led to the explosion," he said.
While NTSB may be working under the assumption that there was a gas leak, Mayor Bill de Blasio declined to be specific as to what the city think led to the explosion that leveled the two buildings on Park Avenue.
"We know there was an explosion but we don’t know everything about the lead-up to it, and that’s why we’re doing a thorough investigation," de Blasio said Thursday. "And by the way, we can only get conclusive evidence when the fire is out, when the rescue is completed and we really get a chance to look at all the facts."
The mayor warned against any premature speculation, adding that the city was focused on finding out exactly what happened Wednesday morning.
"I can tell you that every energy is going to be expended to get down to the truth here and learn from it," he added.
Follow Chester Jesus Soria on Twitter @chestersoria