NEW YORK (PIX11) — Sunday marks 21 years since the attacks on 9/11.

It’s a solemn week as we remember the lives lost and also the sacrifices made by the first responders who rushed to Ground Zero and never looked back. FDNY Battalion Chief Joseph Pfeifer was one of those first responders.

He was on a routine call in Lower Manhattan the morning of 9/11. Pfeiffer watched as a plane crashed into the North Tower, then jumped into action. He was the first FDNY chief on scene.

Though he retired from the FDNY four years ago, Pfeiffer continues his work in counterterrorism and emergency preparedness. He’s set to speak at the UN Global Congress of Victims of Terrorism on Thursday. He also shared his story in “Ordinary Heroes: A Memoir of 9/11.”