Official websites use. Share sensitive information only on official, secure websites. The collapse of the WTC buildings following the terrorist attacks on September 11, , was one of the worst building disasters in US history, killing 2, people, including emergency responders.
NIST responded to calls from Congress and the public to carry out a federal investigation of why the buildings collapsed, the evacuation of building occupants and the emergency response. More than professionals and technical subject matter experts, including 85 NIST staff members, answered the call and participated in the investigation.
As part of the investigation, the NIST team gathered every bit of evidence they could find. Activities included:. Throughout the process, NIST held 23 public meetings and provided multiple opportunities for the public to review and comment on drafts of the reports. Read first-hand accounts of what it was like to work on the WTC investigation in our blog series.
Start with Shyam Sunder's reflections on the investigation and its legacy, and then keep reading for insights on everything from what it was like to catalogue the images and video to how changed one researcher The WTC investigation has had a significant legacy. In the reports, NIST made 31 recommendations for improvements to building and fire codes, standards, and practices based on the WTC investigation.
While the federal government has no regulatory authority for building and fire codes, many U. In addition, NIST scientists conducted tests of steel from the WTC buildings to measure their mechanical properties at normal and elevated temperatures. These tests led to the development and validation of performance criteria for fire resistive steel. This type of steel, which was not available at the time the WTC was built, would not necessarily prevent a building from collapsing during a fire, but it would give occupants more time to escape.
This effort was at the time — and still is — the largest forensic identification effort ever undertaken. At a. Only six people in the World Trade Center towers at the time of their collapse survived. Almost 10, others were treated for injuries, many severe. Because the plane had been delayed in taking off, passengers on board learned of events in New York and Washington via cell phone and Airfone calls to the ground. Knowing that the aircraft was not returning to an airport as the hijackers claimed, a group of passengers and flight attendants planned an insurrection.
One of the passengers, Thomas Burnett, Jr. I love you, honey. Sandy Bradshaw, a flight attendant, called her husband and explained that she had slipped into a galley and was filling pitchers with boiling water. The passengers fought the four hijackers and are suspected to have attacked the cockpit with a fire extinguisher. The plane then flipped over and sped toward the ground at upwards of miles per hour, crashing in a rural field near Shanksville in western Pennsylvania at a. All 44 people aboard were killed.
Its intended target is not known, but theories include the White House , the U. Capitol, the Camp David presidential retreat in Maryland or one of several nuclear power plants along the eastern seaboard.
Citizens of 78 countries died in New York, Washington, D. At the World Trade Center, 2, died after the two planes slammed into the twin towers. That figure includes firefighters and paramedics, 23 New York City police officers and 37 Port Authority police officers who were struggling to complete an evacuation of the buildings and save the office workers trapped on higher floors.
At the Pentagon, people were killed, including 64 on American Airlines Flight 77, the airliner that struck the building. On Flight 93 , 44 people died when the plane crash-landed in Pennsylvania. Bush , who was in Florida at the time of the attacks and had spent the day being shuttled around the country because of security concerns, returned to the White House.
These acts shatter steel, but they cannot dent the steel of American resolve. In a reference to the eventual U. Within two months, U. Osama bin Laden, the mastermind behind the September 11th attacks, remained at large until May 2, , when he was finally tracked down and killed by U. In June , then-President Barack Obama announced the beginning of large-scale troop withdrawals from Afghanistan; it took until August for all U.
It was signed into law by President George W. Bush on November 25, Today, the Department of Homeland Security is a cabinet responsible for preventing terror attacks, border security, immigrations and customs and disaster relief and prevention. Other skyscrapers haven't fully collapsed before because of fire. It says Tower Seven had an unusual design, built over an electricity substation and a subway; there were many fires that burnt for hours; and crucially, fire fighters could not fight the fires in Tower 7, because they didn't have enough water and focused on saving lives.
They think fires burnt long enough to weaken and break many of the connections that held the steel structure together. Most susceptible were the thinner floor beams which required less fireproofing, and the connections between the beams and the columns.
As they heated up the connections failed and the beams sagged and failed, investigators say. The collapse of the first of the Twin Towers does not seem to have caused any serious damage to Tower Seven, but the second collapse of the 1,ft m North Tower threw debris at Tower Seven, just ft m away.
Tower Seven came down at 5. Until now most of the photographs have been of the three sides of the building that did not show much obvious physical damage. Now new photos of the south side of the building, which crucially faced the North Tower, show that whole side damaged and engulfed in smoke. Return to link. Most Popular Now 56, people are reading stories on the site right now. BBC News Updated every minute of every day.
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