As members of Pennsylvania Task Force 1, Philadelphia Fire Department Lt. Michael Foley and Chief John O'Neill were among those deployed to New York City following the terrorist attacks.
Twenty-five years later, both men remain on active duty and are reflecting on an experience they say they will never forget.
"When I saw the building collapse, I knew that we were going to be activated," O'Neill said.
"We got word pretty quickly that the task force, the Pennsylvania task force, was activated and that we were going," Foley added.
Pennsylvania Task Force 1 is a specialized urban search-and-rescue team trained to respond to large-scale disasters.
"We had that hope that we could maybe make a difference as soon as we got there," Foley said.
When the firefighters arrived in Manhattan, the scope of the devastation was difficult to comprehend.
"It's just surreal. You're just looking at this like, 'Wow.' You just can't believe what you're looking at," Foley recalled. "It's hard to process. You just can't fathom that kind of destruction."
"I remember walking up and, in a sense, it looked like it had snowed," O'Neill said. "All the concrete had pulverized and created a white dust over everything at ground zero."
Both men worked alongside members of the FDNY in bucket brigades, spending long hours searching through debris and assisting recovery operations.
"We did get some opportunity to do some searching for possible victims," Foley said. "It turned out there wasn't anybody alive for us to find, but at least we were given some assignments."
O'Neill said the scale of the disaster site was overwhelming.
"Understanding the magnitude of the whole incident area, it is a very large area, not only geographically spread out, but it was also in lower levels underneath the World Trade Center," he said.
For these men, 25 years have passed, but they'll never forget their days at ground zero. They hope others don't forget what happened either.
"I just hope people will remember how tragic of a day that was and not forget the people that lost their lives that day," Foley said.