The exterior wall on the east side of the World Trade Center’s South Tower apparently bows before the building collapses. The first inquiry into the collapse, by the Federal Emergency Management Agency and the American Society of Civil Engineers, states that the perimeter walls bow outward. “Expansion of floor slabs and framing results in outward deflection of columns and potential overload,” the investigation concludes. [Federal Emergency Management Agency, 5/1/2002, pp. 2-25] However, a subsequent report by the National Institute of Standards and Technology states that the east wall of the South Tower bows inward. In places the wall is said to bow inward by between seven and nine inches at floor 80, and NIST interprets this bowing to mean that the floors must be sagging. NIST will find that the sagging and bowing are two of the seven major factors that led to the collapse of each tower, as the bowing walls are no longer able to support their share of the buildings’ weight, causing the buildings to tilt and the upper sections to fall. [National Institute of Standards and Technology, 9/2005, pp. 43-46, 87] A wall in the North Tower also apparently bows before the building collapses (see 10:23 a.m. September 11, 2001).
9:47 a.m. September 11, 2001: Internal Collapse at WTC South Tower Reported
A man who is on the 105th floor of the South Tower calls emergency 9-1-1 to report that floors below his location, “in the 90-something floor,” have collapsed. The 9-1-1 operator types a record of this call into the Special Police Radio Inquiry Network (SPRINT) data link, which will be passed on to the New York fire department’s Emergency Medical Service (EMS). It isn’t known when the call is made exactly, but the EMS Dispatch computer apparently receives the call record at this time. However, because it is classified as a “supplement message,” it is not yet read by anyone. The police dispatcher dealing with the area around the WTC also receives the call record, but misinterprets it as meaning that the floor the person is on has collapsed. EMS dispatchers are dealing with an enormous volume of calls as well as performing many other tasks under extreme pressure during the crisis, so a report later concludes that the EMS operators didn’t have the time to review the information before the collapse of the South Tower at 9:59 (see 9:59 a.m. September 11, 2001), and the fire chiefs never received the information. [New York City Fire Department, 8/19/2002]
9:50 a.m. September 11, 2001: Molten Metal Pours from South Tower
Video footage later reveals that in the minutes immediately before the collapse of the WTC’s South Tower, a stream of molten metal starts pouring out of a window opening around the northeast corner of its 80th floor. FEMA later suggests that this is “possibly aluminum from the airliner,” and comments, “This is of particular interest because, although the building collapse appears to have initiated at this floor level, the initiation seems to have occurred at the southeast rather than the northeast corner.” [Civil Engineering, 5/2002; Federal Emergency Management Agency, 5/1/2002, pp. 2-34; Dwyer and Flynn, 2005, pp. 207] According to the National Institute of Standards and Technology, “The composition of the flowing material can only be the subject of speculation, but its behavior suggests it could have been molten aluminum.” [Pitts, Butler, and Junker, 9/2005, pp. lxxix] However physics professor Steven E. Jones will in 2006 dispute this, saying that molten aluminum is silvery and never turns yellow, like what is in the video footage. He will instead claim the presence of this molten metal supports the theory that explosives, specifically thermite, are what caused the Twin Towers to collapse. He says thermite can cause steel to melt and become yellowish. [Deseret Morning News, 4/10/2006]
9:52 a.m. September 11, 2001: Firefighters Reach 78th Floor of South Tower; Find Two Isolated Fires
Two firefighters climbing up the South Tower, Orio Palmer and Ronald Bucca, have reached its 78th floor, the lower end of the impact zone where Flight 175 hit. [New York Times, 8/4/2002] They are just two floors below the level where, minutes later, its collapse initiates. [Federal Emergency Management Agency, 5/1/2002, pp. 2-34] Over radio, Palmer tells firefighter Joseph Leavey, “We’ve got two isolated pockets of fire. We should be able to knock it down with two lines.” [Dwyer and Flynn, 2005, pp. 206] The fact that they reached so high up the tower only comes to light almost a year later, when a tape of radio communications from 9/11 is made public (see August 4, 2002). The New York Times will report “[N]owhere on the tape is there any indication that firefighters had the slightest indication that the tower had become unstable or that it could fall.” [New York Times, 11/9/2002] Palmer’s communication appears to contradict claims that “extreme fires” contributed to the tower’s collapse. [BBC, 9/13/2001; New York Times, 10/20/2004] Ronald Bucca, a Special Forces veteran, had actually conducted his own private research into Islamic militancy following the 1993 WTC bombing. He’d even taken time, in 1996, to attend the beginning of the trial of Ramzi Yousef, a mastermind of the bombing (see September 5, 1996). [Lance, 2003, pp. 180-183, 333-334]
9:58 a.m. September 11, 2001: Most Workers in South Tower Who Could Evacuate Have Done So
Almost all the occupants of the South Tower who are able to evacuate the building have done so and have crossed the street to safety. Only 11 occupants who were below the impact floors are still in the building when it collapses. However, 619 building occupants in or above the impact zone have either already died or perish in the collapse, as do many emergency workers. [National Institute of Standards and Technology, 9/2005, pp. xxxix, 44] Most workers in the North Tower also leave the building before it collapses (see 10:27 a.m. September 11, 2001).
Before 9:59 a.m. September 11, 2001: EMT Worker Given Message That WTC Towers Are Going to Collapse; High-Level Officials Evacuate Lobby of North Tower
In the lobby of Building 7 of the WTC, EMS Division Chief John Peruggia is in discussion with Fire Department Captain Richard Rotanz and a representative from the Department of Buildings. As Peruggia later describes, “It was brought to my attention, it was believed that the structural damage that was suffered to the [Twin] Towers was quite significant and they were very confident that the building’s stability was compromised and they felt that the North Tower was in danger of a near imminent collapse.” Peruggia grabs EMT Richard Zarrillo and tells him to pass on the message “that the buildings have been compromised, we need to evacuate, they’re going to collapse.” Zarrillo heads out to the fire command post, situated in front of 3 World Financial, the American Express Building, where he relays this message to several senior firefighters. He says, “OEM says the buildings are going to collapse; we need to get out.” (OEM is the Mayor’s Office of Emergency Management, which has its headquarters in WTC 7.) Fire Chief Pete Ganci’s response is, “who the f___ told you that?” Seconds later, they hear the noise of the South Tower as it collapses. [City of New York, 10/23/2001; City of New York, 10/25/2001; City of New York, 10/25/2001; City of New York, 11/9/2001] Others also appear to have been aware of the imminent danger. Fire Chief Joseph Pfeifer, who is at the command post in the lobby of the North Tower, says, “Right before the South Tower collapsed, I noticed a lot of people just left the lobby, and I heard we had a crew of all different people, high-level people in government, everybody was gone, almost like they had information that we didn’t have.” He says some of them are moving to a new command post across the street. [City of New York, 10/23/2001; Firehouse Magazine, 4/2002; Dwyer and Flynn, 2005, pp. 214] Mayor Giuliani also says he receives a prior warning of the first collapse, while at his temporary headquarters at 75 Barclay Street (see (Before 9:59 a.m.) September 11, 2001).
Shortly Before 9:59 a.m. September 11, 2001: Ground Shakes Prior to South Tower Collapse
Some witnesses near the World Trade Center feel the ground shaking just before the South Tower starts to collapse: 
EMT Joseph Fortis is heading across West Street, when, he says, “the ground started shaking like a train was coming.” He then looks up and sees the South Tower starting to collapse. [City of New York, 11/9/2001] Lonnie Penn, another EMT, is outside the Marriott Hotel, which is adjacent to the North Tower. He and his partner “felt the ground shake. You could see the towers sway and then it just came down.” [City of New York, 11/9/2001] Bradley Mann is at the EMS staging area on Vesey Street. He says, “Shortly before the first tower came down I remember feeling the ground shaking. I heard a terrible noise, and then debris just started flying everywhere.” [City of New York, 11/7/2001] Battalion Chief Brian O’Flaherty is walking into the lobby of the Marriott Hotel. He says, “I hear a noise. Right after that noise, you could feel the building start to shudder, tremble, under your feet.” He then hears the “terrible noise” of the South Tower collapsing. [City of New York, 1/9/2002] Witnesses will also notice the ground shaking before the North Tower collapses (see Shortly Before 10:28 a.m. September 11, 2001).
Before 9:59 a.m. September 11, 2001: Mayor Giuliani Apparently Told WTC Towers Will Collapse When Fire Chiefs Think Otherwise
Between 9:25 a.m. and 9:45 a.m., one senior New York fire chief recommends to the Fire Department Chief of Department that there might be a WTC collapse in a few hours, and, therefore, fire units probably shouldn’t ascend much above the sixtieth floor (presumably this assumes the collapse would be gradual so those on lower floors would still have time to evacuate). This advice is not followed or not passed on. Apparently, no other senior fire chiefs mention or foresee the possibility of the WTC towers falling. [9/11 Commission, 5/19/2004] However, New York City Mayor Rudolph Giuliani later recounts, “I went down to the scene and we set up headquarters at 75 Barclay Street, which was right there, with the police commissioner, the fire commissioner, the head of emergency management, and we were operating out of there when we were told that the World Trade Center was going to collapse. And it did collapse before we could actually get out of the building, so we were trapped in the building for ten, 15 minutes, and finally found an exit and got out, walked north, and took a lot of people with us.” [ABC News, 9/11/2001] As can be seen by another account of similar events, this happens before the first WTC tower falls, not the second. [9/11 Commission, 5/19/2004] It is not clear who tells Giuliani to evacuate when no fire chiefs were considering the possibility of an imminent collapse. However, an EMT is also given a message around this time, warning that the towers are going to collapse. The origin of this information is apparently the Mayor’s Office of Emergency Management, so this may also have been from where Giuliani heard of the imminent collapse (see (Before 9:59 a.m.) September 11, 2001).
9:59 a.m. September 11, 2001: South Tower of WTC Collapses
The South Tower of the World Trade Center tilts to the southeast and then collapses. It was hit by Flight 175 at 9:03 a.m., 56 minutes earlier (see 9:03 a.m. September 11, 2001). [Washington Post, 9/12/2001; New York Times, 9/12/2001; MSNBC, 9/22/2001; USA Today, 12/20/2001; Associated Press, 8/21/2002; ABC News, 9/11/2002; National Institute of Standards and Technology, 9/2005, pp. 44] The first sign of the collapse is visible on floor 82. [National Institute of Standards and Technology, 9/2005, pp. 87] The angle of the tilt will be disputed after 9/11 (see September-November 2005), as will the time it takes the towers to fall to the ground (see September 12, 2001-September 2005). [Scientific American, 10/9/2001; Eagar and Musso, 12/2001; PBS Nova, 5/2002; National Institute of Standards and Technology, 8/30/2006]
9:59 a.m. September 11, 2001: Some Witnesses Hear Explosions as South Tower Collapses
Numerous witnesses, including firefighters and other rescue workers, hear explosions at the start of, and during, the collapse of the south WTC tower. Some of them report hearing a single explosion: Jeff Birnbaum: “There was an explosion and the whole top leaned toward us and started coming down.” [Electrical Wholesaling, 2/1/2002] Battalion Chief John Sudnik: “[W]e heard a loud explosion or what sounded like a loud explosion and looked up and I saw Tower Two start coming down.” [City of New York, 11/7/2001] Firefighter Edward Kennedy hears “a tremendous boom, explosion… and the top of the building was coming down at us.” [City of New York, 1/17/2002] Firefighter Edward Sheehey hears “an explosion, looked up, and the building started to collapse.” [City of New York, 12/4/2001] Battalion Chief Thomas Vallebuona: “I heard ‘boom,’ an exploding sound, a real loud bang. I looked up, and I could see the Trade Center starting to come down.” [City of New York, 1/2/2002] EMT Julio Marrero: “I heard a loud bang. We looked up, and we just saw the building starting to collapse.” [City of New York, 10/25/2001]
Other witnesses report hearing multiple explosions: Journalist Pete Hamill: “We heard snapping sounds, pops, little explosions, and then the walls bulged out, and we heard a sound like an avalanche.” [New York Daily News, 9/11/2001] Police officer Sue Keane, who is an Army veteran, is located in the north WTC tower: “[I]t sounded like bombs going off. That’s when the explosions happened.… It started to get dark, then all of a sudden there was this massive explosion.” [Hagen and Carouba, 2002, pp. 65] Firefighter Keith Murphy, who is in the lobby of the North Tower: “[T]he first thing that happened, which I still think is strange to me, the lights went out.… I had heard right before the lights went out, I had heard a distant boom boom boom, sounded like three explosions.… At the time, I would have said they sounded like bombs, but it was boom boom boom and then the lights all go out.… I would say about 3, 4 seconds, all of a sudden this tremendous roar.” [City of New York, 12/5/2001] Firefighter Craig Carlsen hears “explosions coming from building two, the South Tower. It seemed like it took forever, but there were about ten explosions.… We then realized the building started to come down.” [City of New York, 1/25/2002] Firefighter Thomas Turilli, who is in the lobby of the North Tower: “[A]ll of a sudden you just heard like it almost actually that day sounded like bombs going off, like boom, boom, boom, like seven or eight, and then just a huge wind gust just came… It just seemed like a huge explosion.” [City of New York, 1/17/2002] Firefighter Stephen Viola: “[T]hat’s when the South Tower collapsed, and it sounded like a bunch of explosions. You heard like loud booms.” [City of New York, 1/10/2002] Firefighter Lance Lizzul: “[W]e heard some bangs. That made us look up, and that’s when the first Trade Center came down.” [City of New York, 12/10/2001] Paramedic Kevin Darnowski: “I heard three explosions, and then we heard like groaning and grinding, and Tower Two started to come down.” [City of New York, 11/9/2001]
However, the National Institute of Standards and Technology, which conducts a three-year study of the WTC collapses, will subsequently claim it found “no corroborating evidence for alternative hypotheses suggesting that the WTC towers were brought down by controlled demolition using explosives” (see October 26, 2005). [National Institute of Standards and Technology, 9/2005, pp. 146]
