"It's something that stays with you, for sure," FDNY Commissioner Daniel Nigro said. "343 is a number that no one could imagine."
That's how many firefighters lost their lives when the World Trade Center towers collapsed.
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Twenty years later, Nigro is still amazed at the commitment of his members to save lives on that tragic day.
"Every member that entered knew that they were entering the most dangerous building they had ever entered into in their career," he said. "And yet, all of them did what they pledged to do."
Nigro became chief in an instant. His boss, Chief Pete Ganci, who had escaped the collapse of the south tower, was killed when the north tower came down.
"Our plan was to rescue as many people as we could, to perhaps get to the point of impact, get a stairway clear, and be able to get people down who were trapped above the fire," he said. "We simply ran out of time."
The commissioner still feels the pain of each loss and their families' heartbreak.
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"Knowing that you were in charge of this operation and this is what occurred is a heavy burden," Nigro said.
But there was no way to realize how much time firefighters had, since the buildings survived the initial impacts of American Airlines flight 767 crashing into the north tower and minutes later United Airlines flight 175 slamming into the south tower.
"We understood that we would have localized collapse in the areas where the impact occurred and above, but the collapse of the building, no," he said. "No building had ever collapsed from, a high rise building, from a structural fire. So there was nothing to be guided by."
So this 20th anniversary comes with very little closure for those so close to the tragedy. For them, every day brings moments of reflection.
"I don't think we'll ever get over it," he said. "That's impossible."
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So when the commissioner gathers at the site to hear the names on this anniversary, he will remember all who have sacrificed so much.
"So many of them I knew, so you hear the name and you see the person in your mind, and maybe you see their families," he said. "It's very powerful."
CLICK HERE for more Eyewitness News reflections, photos and stories marking the anniversary of 9/11
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