They were among the heroes of the September 11, 2001 attacks, the first responders who rushed to the World Trade Center site to search for survivors.
But they worked mostly in anonymity.
Now, photographer Andrea Booher pays tribute to the men and women who toiled at "the pile," with a showcase of her work in the "Hope at Ground Zero" exhibition opening Friday at the National September 11 Memorial and Museum which now occupies the site in downtown New York. It runs through May 2017.
"In the beginning it was firefighters, volunteers, search and rescue, police. Everybody had sort of a different approach to how they were searching for survivors," she said. "The only goal was trying to find survivors in the pile."
Booher, a photographer for the Federal Emergency Management Agency (FEMA), had arrived at the site the evening of September 11 and was assigned along with colleague Michael Rieger to document the aftermath of the deadliest terror attack on US soil.
She ended up staying two and a half months.
"I really felt that it was an incredible honor but it was a lot of responsibility," she said. "I pushed myself to my limit workwise and in every aspect."
In the early days, the work was frantic as rescuers searched for survivors.
But around September 20, "I showed up at the site. Nobody said anything, but it was just like this very depressing feeling, very heavy feeling at the site," Booher said.
"It was kind of rainy, and it was just... there was no energy. You had just the feeling that it was over, that the hope was gone. We weren't going to bring (out) anyone else. It kind of switched to a recovery mission at that point."
Twenty people were found alive in the rubble, the last one September 12. In all, the attack in New York claimed 2,753 victims.
- "The best in humanity" -
Booher, a veteran of many major disasters, initially had access to the World Trade Center site but not the pile that was the remains of the Twin Towers.
But over time, the firefighters who were running the site began to trust Booher and Rieger after seeing them working "every day, all hours."
The firefighters, who lost hundreds of their comrades in the attack, noticed that the pair always put their cameras down and didn't take photos when bodies were recovered, out of respect.
"So there was a certain trust that was built up. That was why we were able to gain access to the pile. There was this bond," she said.
Her subjects posed amid grotesque tangles of giant steel beams, alone or in groups, with blackened faces like those of coal miners.
"To this day, I have that bond with so many of the people that are in those photographs," Booher said, noting that she and Rieger later sent more than 600 CDs of images to the people they met. "We keep in touch, we check on each other."
"Most people think of disaster as just this traumatic experience, but ... as horrific as it was you also saw this incredibly human side of people come forward," she said. "I think it's when you see the best in humanity."