His youngest daughter, Rachel — only 3 at the time of the 9/11 attacks — shares her father's commitment by volunteering at the museum on Saturday afternoons.

"People all over the world have told me stories, that they remember what they were wearing, where they were when they heard that the buildings had been attacked," she said. "So just seeing that opened my eyes to how it really affected the whole world, and not just the surrounding community or people who were in the towers — it had a global impact."

"Sometimes when I come in with my dad and I see him talking about certain artifacts and stuff and adding his personal experience with it, it kind of makes me kind of emotional just knowing that he was there and what he went through," she said. "I think he does it honestly to get closure from everything that happened, not only being here but losing his best friend — and to really give back and teach future generations about what happened so no one forgets."

In 2015, her father had to find new office space for his company, ink and toner retailer Cartridge World. He chose, of all places, One World Trade — becoming the first and only tenant from the twin towers to move into the new building. "A lot of people will ask me, you know, 'Do you regret it? Are you nervous?' And I'm really not. Not at all. I don't regret it a little bit. I just find it the beginning of a new life for me."

As surprising as his decision may be to others, for Carafello, it was rather simple. "I don't think Americans are built to run away," he said. "There's a resurgence going on. It's a rebuilding and a rebirth. I think that's what we do — we build 'em bigger, and better, stronger, and so on. And that's the pride of being here, really."

Fifteen years after the 9/11 attacks, Carafello divides his time between his 85th floor office at One World Trade and the 9/11 museum below. "He's a great role model, definitely, and someone I look up to," said Rachel Carafello. "He works so hard, and the fact that he makes time in his busy schedule to come and volunteer and really make an impact on the people visiting and to educate people, I think it says a lot about him as a person."

Tune in to Ground Zero Rising: Freedom vs. Fear, Thursday Sept. 1 at 10 p.m. ET on CNBC.