The September 11 attacks of 2001 caused the deaths of 2,996 people, including 2,977 victims and 19 hijackers who committed murder–suicide. Thousands more were injured, and long-term health effects have arisen as a consequence of the attacks. New York City took the brunt of the death toll when the Twin Towers of the World Trade Center complex in Lower Manhattan were attacked, with an estimated 1,600 victims from the North Tower and around a thousand from the South Tower. Two hundred miles southwest in Arlington County, Virginia, another 125 were killed in the Pentagon. The remaining 265 fatalities included the ninety-two passengers and crew of American Airlines Flight 11, the sixty-five aboard United Airlines Flight 175, the sixty-four on American Airlines Flight 77 and the forty-four who boarded United Airlines Flight 93. The attack on the World Trade Center's North Tower single-handedly made 9/11 the deadliest act of terrorism in human history.
Most of those who perished were civilians except for 343 members of the New York City Fire Department and 71 law enforcement officers who died in the World Trade Center and on the ground in New York City; a United States Fish and Wildlife Service Office of Law Enforcement officer who died when United Airlines Flight 93 crashed into a field near Shanksville, Pennsylvania; 55 military personnel who died at the Pentagon in Arlington County, Virginia; and the 19 terrorists who died on board the four aircraft. At least 102 countries lost citizens in the attacks.
Initially, a total of 2,603 victims were confirmed to have been killed at the World Trade Center site. In 2007, the New York City medical examiner's office began to add people who died of illnesses caused by exposure to dust from the site to the official death toll. The first such victim was a woman, a civil rights lawyer, who had died from a chronic lung condition in February 2002. In September 2009, the office added a man who died in October 2008, and in 2011, a male accountant who had died in December 2010. This is what raises the number of victims from the World Trade Center site to 2,606, and the overall 9/11 death toll to 2,996.
, medical authorities concluded that 1,140 people who worked, lived, or studied in Lower Manhattan at the time of the attacks have been diagnosed with cancer as a result of "exposure to toxins at Ground Zero". In September 2014, it was reported that over 1,400 rescue workers who responded to the scene in the days and months after the attacks had since died. At least 10 pregnancies were lost as a result of 9/11. Neither the FBI nor New York City officially recorded the casualties of the 9/11 attacks in their crime statistics for 2001, with the FBI stating in a disclaimer that "the number of deaths is so great that combining it with the traditional crime statistics will have an outlier effect that falsely skews all types of measurements in the program's analyses."
Evacuation
Most tall buildings in the United States at the time were not designed for complete evacuation during a crisis, even after the 1993 World Trade Center bombing. It was also procedural for announcements in the case of high-rise fire safety for individuals to remain in their offices unless they were near the burning floor. However, after it took ten hours to completely evacuate the towers in the 1993 attack, multiple additions were made to the buildings and evacuation plans. Radio repeaters were installed in the towers to improve communication, battery powered emergency lights were installed, and fire drills held. Individuals who evacuated for both the 1993 and 2001 attacks reportedly stated they were better prepared for the 2001 evacuations. At least two individuals who had evacuated in both 1993 and 2001 later reported that they had prepared for a potential evacuation after 1993, by bringing either an item such as a flashlight or an emergency preparedness bag with them.
Both 110-story towers housed three stairwells in the central cores of each. On maintenance floors containing lift and ventilation machinery (such as some of the floors where Flight 175 struck the South Tower), the northern and southern stairwells entered corridors extending north and south to stairwells that bypassed the heavy equipment. The three stairwells―labeled A, B, and C―were as tall as the buildings, with two built to in width and the third being wide. In the North Tower the stairs were approximately 70 ft apart, compared to the distance of 200 ft between the stairwells in the South Tower.