World Trade Center Facts and Statistics

Design and Construction

Work on foundations began in 1966. Construction began in 1968.

The foundation for each tower extended more than 70 feet below ground, resting on solid bedrock. More than 1.2 million cubic yards of earth and rock were excavated to make way for the World Trade Center. The excavated material was placed in the Hudson River to create 23.5 acres of land deeded to the City of New York. This landfill is now Battery Park City.

More than 200,000 tons of steel was used in the World Trade Center's construction. The 425,000 cubic yards of concrete used in building the World Trade Center is enough to build a 5-foot-wide sidewalk from New York City to Washington, D.C.

The steel inside the WTC could have made three more Brooklyn Bridges.

There were 43,600 windows in the Twin Towers with over 600,000 square feet of glass window area cleaned by automatic window washing machines traveling on stainless steel tracks.

Each tower had 110 stories and was around 1,360 feet tall. (The roof of WTC1 was 1,368 feet above concourse level, 6 feet taller than WTC2, and supported a 360-foot antenna.) Each floor was 50,000 square feet (approximately one square acre) with each internal wall measuring 206 feet in length.

The 360-foot television mast atop One World Trade Center supported 10 main television antennas, numerous auxiliary antennas and a master FM antenna.

The buildings had their own ZIP codes — 10047 and 10048.

Each tower contained three central stairwells, which ran essentially from top to bottom, and 99 elevators. The sky lobby express elevators were capable of carrying 55 people, with a 10,000-pound capacity. Express elevators traveled at speeds of up to 27 feet per second.

Stairwells A and C ran from the 110th floor to the raised mezzanine level of the lobby. Stairwell B ran from the 107th floor to level B6, six floors below ground, and was accessible from the West Street lobby level, which was one floor below the mezzanine.

All three stairwells ran essentially straight up and down, except for two deviations in stairwells A and C where the staircase jutted out toward the perimeter of the building. On the upper and lower boundaries of these deviations were transfer hallways contained within the stairwell proper.

Each hallway contained smoke doors to prevent smoke from rising from lower to upper portions of the building; they were kept closed but not locked. Doors leading from tenant space into the stairwells were never kept locked; reentry from the stairwells was generally possible on at least every fourth floor.

Occupants and Safety Systems

On any given workday, up to 50,000 office workers occupied the World Trade Center, and 40,000 people passed through the complex.

The World Trade Center contained the offices of 430 businesses from 26 different countries.

Doors leading to the roof were locked. There was no rooftop evacuation plan. The roofs of both the North Tower and the South Tower were sloped and cluttered surfaces with radiation hazards, making them impractical for helicopter landings and as staging areas for civilians. Although the South Tower roof had a helipad, it did not meet 1994 Federal Aviation Administration guidelines.

To manage fire emergency preparedness and operations, the Port Authority created the dedicated position of fire safety director. The director supervised a team of deputy fire safety directors, one of whom was on duty at the fire command station in the lobby of each tower at all times.

Deputy fire safety directors conducted fire drills at least twice a year, with advance notice to tenants. "Fire safety teams" were selected from among civilian employees on each floor and consisted of a fire warden, deputy fire wardens, and searchers.

Most civilians recall simply being taught to await the instructions that would be provided at the time of an emergency. Civilians were not informed that rooftop evacuations were not part of the evacuation plan, or that doors to the roof were kept locked.

The Port Authority acknowledges that it had no protocol for rescuing people trapped above a fire in the towers.

The World Trade Center lacked any plan for evacuation of civilians on upper floors in the event that all stairwells were impassable below.

Between 16,400 and 18,800 civilians were in the World Trade Center complex at 8:46 a.m. on Sept. 11, 2001.

Approximately 87 percent of the estimated 17,400 occupants of the towers, and 99 percent of those located below the impact floors, evacuated successfully.

A principal factor limiting the loss of life was that the buildings were one-third to one-half occupied at the time of the attacks. The National Institute of Standards and Technology (NIST) estimated that if the towers had been fully occupied with 20,000 occupants each, it would have taken just over three hours to evacuate the buildings and about 14,000 people might have perished because the stairwell capacity would not have been sufficient to evacuate that many people in the available time.

Sources: Final Report of the National Commission on Terrorist Attacks on the United States (July 22, 2004); National Institute of Standards and Technology, Final Report on the Collapse of the World Trade Center Towers (September 2005), September 11 News (Web site); World Trade Center Facts (Web site)