A truck from Ladder Company 131 based on Brooklyn, N.Y., is caked in dust and ash after racing to the World Trade Center site Sept. 11, 2001. More than 14,500 firefighters took part in the 9/11 response, rescue and recovery efforts, many working through the night to comb the rubble for remains.

New York City Fire Department ladder truck 58 from the South Bronx pours water on a collapsed building in the World Trade Center complex Sept. 11, 2001. A firefighter in the foreground is videotaping the scene. The Fire Department is one of the largest contributors to the collection of photos, artifacts, and oral histories being gathered by the National September 11 Memorial and Museum, which will put them on display in 2012.

A New York City Fire Department GMC Suburban was torched by an explosion following the attacks Sept. 11, 2001, at the World Trade Center. Of the roughly 14,000 firefighters who responded after two commercial jetliners struck the Twin Towers, 343 lost their lives.

New York City Firefighters from Brooklyn-based Ladder Company 146 spray water on the collapsed rubble at Ground Zero on Sept. 11, 2001. Bright rays of sunshine managed to break through the thick clouds of black smoke and dust as night begins to fall.

7 World Trade Center, a trapezoidal building adjacent to the Twin Towers, was effectively destroyed Sept. 11, 2001. Part of the building and an overhead walkway to the World Trade Center plaza, seen here, remain standing immediately following the attack.

An elevated walkway connecting 7 World Trade Center to the World Trade Center plaza remains standing after the Twin Towers' collapse Sept. 11, 2001. A panel created by Mayor Michael Bloomberg to represent those affected by WTC damages estimated that the cost to evaluate and treat those affected or potentially affected by the terrorist attack could exceed $392 million per year.

Chunks of steel, aluminum and concrete, shards of glass and a layer of white ash fill the streets of lower Manhattan around the World Trade Center on Sept. 11, 2001. New York City firefighters assess damage to one of the buildings still standing at the complex.

Thick smoke and toxic fumes continued to rise from the devastation of the World Trade Center towers in lower Manhattan. Recovery workers wearing face masks survey the scene looking for human remains in the hours after the tragedy. Nearly 3,000 people died in the attacks including 343 firefighters, 23 NYPD officers, 37 Port Authority police officers, and thousands of civilians. Many survivors and rescue workers would later be diagnosed with chronic upper and lower respiratory conditions that are believed to be tied to inhalation of the air at Ground Zero.

Thick gray ash covered the streets near Ground Zero on Sept. 11, 2001. In the days that followed, many New Yorkers felt motivated to scoop up samples of the highly pulverized residue and save it in baggies and juice bottles and jars. They did it "not really knowing what it meant," said Jan Ramirez, curator of the National September 11 Memorial and Museum, "yet sensing there was something almost nuclear about it that they felt they should save."

Firefighters climb atop the massive pile of debris as darkness sets in on the night of Sept. 11, 2001. Investigators estimate only 20 percent of workers at the site were protected by face masks in the initial days after the towers fell. In the background, a piece of the iconic outer skeleton of one of the World Trade Center towers remains standing. The National September 11 Memorial and Museum will display surviving beams from the towers when it opens in 2012.

A New York City Fire Department ladder truck lays upside down, buried beneath collapsed steel and concrete of the World Trade Centers. Two exposed wheels on the truck are missing their rubber tires, which presumably melted away in the heat of the fire after the towers collapsed. In the aftermath of 9/11, President George W. Bush promised $20 billion toward the recovery of lower Manhattan and Congress passed several emergency appropriations to provide billions more in financial assistance.

Thousands of pages of white office paper blanketed lower Manhattan after the collapse of the World Trade Center towers Sept. 11, 2001. New Yorkers who collected sheets from their rooftops, in window wells and on fire escapes of buildings nearby have submitted the documents to the National September 11 Memorial and Museum for preservation.