What are shown in these photographs became a part of the National September 11 Memorial & Museum in New York on Aug 22, 2011. The museum, which occupies seven stories below the ground at the World Trade Center site, is due to open in 2012, on the 11th anniversary of the attacks.

A fire helmet that belonged to Chief Joseph Pfeifer.

Joseph Pfiefer, the battalion chief of Engine 7, Ladder 1, was on a routine call in downtown Manhattan when he heard the roar of American Airlines Flight 11 passing overhead on course to the North Tower of the World Trade Center. His unit was one of the first to arrive at the scene, and he set up a command center in the North Tower's lobby. That day, he was being followed by two French filmmaker-brothers, Jules and Gedeon Naudet, and their footage from the scene shows Pfiefer's brother Kevin, also a firefighter in a different unit, preparing to head upstairs for the unfolding rescue mission. When the South Tower collapsed, Pfiefer radioed evacuation orders to his officers in the North Tower. Pfiefer, along with the rest of Ladder 1, survived that day. His brother did not.

A recovered FDNY Squad 252 helmet that belonged to deceased FDNY member, Kevin M. Prior.

Kevin Prior, a firefighter with Brooklyn's Squad 252, can be seen in video footage of the North Tower lobby recorded after the first plane hit, getting ready to go upstairs. Responding to a Mayday call sent out by fellow firefighters encountering breathing problems, he and five other members of the squad are thought to have been on a floor in the 20s when the tower collapsed. Prior's body was found three weeks after the attacks and buried on Long Island, but his mother was troubled that his helmet had not been returned to the family, and said as much in a television interview. An employee at the city's Office of the Chief Medical Examiner happened to catch the broadcast, recognized Prior's squad and badge numbers, and hand-delivered the badly damaged helmet to his grateful family.