While the nation remembers the terrorist attacks that killed thousands of Americans more than 20 years ago, New York City firefighters who survived after being sent to rescue victims at the World Trade Center will relive a life-changing experience that’s now a part of who they are. “It’s a day that will never leave you,” former Fire Department of New York Commissioner Dan Nigro tells Scott Pelley. Nigro and other firefighters who were at Ground Zero, many of whom fill the top ranks of the FDNY, recall the men, their sacrifices and the tragedy of losing 343 of their colleagues. This segment runs the full hour. Maria Gavrilovic is the producer.