[Buscemi] showed up at his old firehouse the day after the World Trade Center tragedy in New York to volunteer. Worked twelve hour shifts for a week after the terrorist act, digging through rubble with his old comrades looking for missing firefighters... anonymously. [September 2001]
I remember reading about this after it happened. IIRC, the account was later confirmed in several magazines. There was even a FR thread about it:
Actor and Former NYC Firefighter Steve Buscemi Rumoured to be Digging Out Rubble at WTC Site
Has Buscemi ever spoken in public about this?