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Joseph Pfeifer remembers 9/11 in a way few others can - as the first FDNY chief to arrive at the Twin Towers.
Pfeifer has collected his memories in a new book, Ordinary Heroes: A Memoir of 9/11.
He and his crew were already at the towers that morning, checking on reports of a gas leak. Pfeifer heard "a loud noise of a plane" and saw it flying low. He knew immediately that it was a terrorist attack and ordered his crew to start evacuating the building.
Pfeifer's brother Kevin was among the 343 firefighters who lost their lives on that day - but more than 20,000 people were saved.