World Trade Center Demolition

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Drills successful planting bombs in 10 buildings, including DHS offices: GAO:

WTC2 (South Tower) 9:59AM EDT 09/11/01

WTC1 (North Tower) 10:28AM EDT 09/11/01

Background Information:

World Trade Center Towers Design and Construction

World Trade Center Demolition Warning

Explosions Occurred In Each Tower Almost Simultaneously With Each Jet Impact

Data Sources:

World Trade Center Demolition Videos

World Trade Center 2 Demolition Images

World Trade Center 1 Demolition Images

World Trade Center Seismic Signal

World Trade Center Dust

World Trade Center Debris Field Distribution

World Trade Center Disaster Site Images

Column Ends

World Trade Center Hot Spots

Recovered World Trade Center Steel At NIST

First Responder Interviews

FOIA Release - 3,160 Electronic Records of The WTC Collapse Investigation:

Data Analysis:

Journal Of 9/11 Studies 2006-08-26 - - 118 Witnesses: The Firefighters' Testimony to Explosions in the Twin Towers (link)

World Trade Center Demolition Acceleration

Explosion Sounds At The World Trade Center

World Trade Center NIST Collapse Simulation


The Gravitational Potential Energy Of Each World Trade Center Tower Was Vastly Insufficient To Cause The Observed Events

The WTC Towers were destroyed by an accelerating wave of destruction

The Size And Shape Of The WTC Debris Pile Is Inconsistent With A Gravitationally Driven Progressive Collapse

The Contents Of The WTC Debris Pile Are Inconsistent With A Gravitationally Driven Progressive Collapse

The Distribution of the WTC Debris is Inconsistent With A Gravationally Driven Collapse

The World Trade Center Towers Were Destroyed By Thousands Of Explosions

Symmetrical Sets Of Focused Explosions Are Visible Far Below The Towers' Accelerating "Collapse" Zone

World Trade Center Exterior Support Columns Were Ejected Up To 600ft From The Base Of The Buildings

The Top Of WTC2 Rotated 22 Degrees And Then Exploded In Mid Air

The Top Of WTC1 Abruptly Accelerated Downward At 64% g Through What Should Be The Path Of Greatest Resistance

The World Trade Center Columns Have Explosive Blast Damage

The Majority of World Trade Center Core Columns Visible In The Debris Pile Are Separated At Their Wield Points

The People Inside The World Trade Center Towers Were Blown To Pieces

The Vast Majority Of The Mass Of The Twin Towers Landed Outside Of The Building Footprints

The Mass Of The Building Was Not Available To Impact And Destroy The Undamaged Structure Below

The Undamaged Structure Below The Jet Impact Zone Was Completely Destroyed

The Distribution Of Mass Ejected From The Twin Towers Was Unnaturally Symmetrical

The Dust Of The World Trade Center Contains The Byproducts Of Explosives

The Dust Of The World Trade Center Contains Explosives

Parts Of The Central Core Of Each Tower Briefly Remained Standing

The Destruction Of Each World Trade Center Tower Generated A Hot Density Current

The Top Of Each World Trade Center Tower Moved Down With A Rapid Onset Of Constant Acceleration

The Normal Contents Of A Office Building Are Not Found In The Debris Field

The Radio Tower On Top Of WTC1 Begins To Drop Before The Building's Roof Line Moves

Explosions Went Off On The Floors Above The Collapse Initiation Floors In Each Tower At The Onset Of Collapse

World Trade Center Tower Steel Sample Shows Severe Damage Due To A High Temperature Corrosion Attack Which Melted The Steel

Internal Collapse Reports

Buildings Still Standing on 9/12

World Trade Center Demolition Links


The WTC incident was unique in that this was the first time ever that a steel-frame high-rise building had collapsed - anywhere in the world. -John O'Connell - Fire Engineering Magazine Oct 2002 (

"It appeared to me that charges had been placed in the building," said Mr. Hamburger, chief structural engineer for ABS Consulting in Oakland, Calif. Upon learning that no bombs had been detonated, "I was very surprised," said Mr. Hamburger. The buildings "certainly did not do as well as I would have hoped." (

Televised images of the attacks on the World Trade Center suggest that explosives devices caused the collapse of both towers, a New Mexico Tech explosion expert said Tuesday. The collapse of the buildings appears "too methodical" to be a chance result of airplanes colliding with the structures, said Van Romero , vice president for research at New Mexico Institute of Mining and Technology. "My opinion is, based on the videotapes, that after the airplanes hit the World Trade Center there were some explosive devices inside the buildings that caused the towers to collapse," Romero said. (

Jack Kelly, a war correspondent for USA Today stated that the FBI believed that bombs in the buildings brought them both down. (video)

"I don't have a clue," says Loizeaux, regarding the cause of the telescoping. He wonders whether there was an explosion at the base of the building. "I don't understand," he adds, unless there was another "agency," at work, he says.[1]

NY Fire Department Chief of Safety stated there were "bombs" and "secondary devices", which caused the explosions in the buildings. (video) (source)

NYC firefighters who witnessed attacks stated "floor by floor it started popping out" .. "it was if... if they had detonators planned to take down a building... boom boom boom boom boom boom boom boom boom" (video) (source)

Louie Cacchioli, a firefighter assigned to Engine 47 in Harlem stated "I was taking firefighters up in the elevator to the 24th floor to get in position to evacuate workers. On the last trip up a bomb went off. We think there was bombs set in the building." (

Rich Sanchez, a MSNBC reporter stated that police had found a suspicious device "and they fear it could be something that might lead to another explosion" and the police officials believe "that one of the explosions at the world trade center . . . may have been caused by a van that was parked in the building that may have had some kind of explosive device in it, so their fear is that there may have been explosive devices planted either in the building or in the adjacent area" (video)

At that point a debate began to rage because the perception was that the building looked like it had been taken out with charges. We had really no concept of the damage on the east side of 2 World Trade Center at that point, and at that point many people had felt that possibly explosives had taken out 2 World Trade, and officers were gathering companies together and the officers were debating whether or not to go immediately back in or to see what was going to happen with 1 World Trade at that point. The debate ended pretty quickly because 1 World Trade came down. -Firefighter Christopher Fenyo FDNY Engine 35

“Somewhere around the middle of the World Trade Center, there was this orange and red flash coming out. Initially it was just one flash. Then this flash just kept popping all the way around the building and that building had started to explode. The popping sound, and with each popping sound it was initially an orange and then red flash came out of the building and then it would just go all around the building on both sides as far as I could see. These popping sounds and the explosions were getting bigger, going both up and down and then all around the building. I went inside and told everybody that the other building or there was an explosion occurring up there and said think we have another major explosion. I don't know if we are all going to be safe here" (nytimes.com_p15) (source)

I heard 3 loud explosions. I look up and the north tower is coming down now, 1 World Trade Center. -Gregg Brady FDNY Battalion 4, EMT

I was with an officer from Ladder 146, a Lieutenant Evangelista, who ultimately called me up a couple of days later just to find out how I was. We both for whatever reason - again, I don't know how valid this is with everything that was going on at that particular point in time, but for some reason I thought that when I looked in the direction of the Trade Center before it came down, before No. 2 came down, that I saw low-level flashes. In my conversation with Lieutenant Evangelista, never mentioning this to him, he questioned me and asked me if I saw low-level flashes in front of the building, and I agreed with him because I thought -- at that time I didn't know what it was. I mean, it could have been as a result of the building collapsing, things exploding, but I saw a flash flash flash and then it looked like the building came down.

Q. Was that on the lower level of the building or up where the fire was?

A. No, the lower level of the building. You know like when they demolish a building, how when they blow up a building, when it falls down? That's what I thought I saw. And I didn't broach the topic to him, but he asked me. He said I don't know if I'm crazy, but I just wanted to ask you because you were standing right next to me. He said did you see anything by the building? And I said what do you mean by see anything? He said did you see any flashes? I said, yes, well, I thought it was just me. He said no, I saw them, too. I don't know if that means anything. I mean,

I equate it to the building coming down and pushing things down, it could have been electrical explosions, it could have been whatever. But it's just strange that two people sort of say the same thing and neither one of us talked to each other about it. I mean, I don't know this guy from a hole in the wall. I was just standing next to him. I never met the man before in my life. He knew who I was I guess by my name on my coat and he called me up, you know, how are you doing? How's everything? And, oh, by the way did you ... It was just a little strange.

Q. On the television pictures it appeared as well, before the first collapse, that there was an explosion up on the upper floors.

A. I know about the explosion on the upper floors. This was like eye level. I didn't have to go like this. Because I was looking this way. I'm not going to say it was on the first floor or the second floor, but somewhere in that area I saw to me what appeared to be flashes. I don't know how far down this was already. I mean, we had heard the noise but, you know, I don't know. -Commissioner Stephen Gregory FDNY Bureau of Communications

"When we reached the 15th floor, the building began to vibrate and shake. I heard loud explosions and rumblings in the background. The stairwell shifted and gave out a large metal on metal groan. The stairwell then twisted back into place with another loud groan. The lights went out. At that point the stairwell became filled with smoke and dust." (nytimes.com_p58_59)

"I just remember there was just an explosion. It seemed like on television when they blow up these buildings. It seemed like it was going all the way around like a belt, all these explosions."(

Chief of NY Fire Department (Citywide Tour Commander) said "there was what appeared to be at first an explosion. It appeared at the very top, simultaneously from all four sides, materials shot out horizontally. And then there seemed to be a momentary delay before you could see the beginning of the collapse" (nytimes.com_p4)

British newspaper stated "In New York, police and fire officials were carrying out the first wave of evacuations when the first of the World Trade Centre towers collapsed. Some eyewitnesses reported hearing another explosion just before the structure crumbled. Police said that it looked almost like a "planned implosion" designed to catch bystanders watching from the street." (

"periodically you would hear a loud boom go off at the top of tower one. As the building continued to burn and emergency equipment kept on responding stirring up the dust and debris in the streets. After approximately 15 minutes suddenly there was another loud boom at the upper floors, then there was a series of smaller explosions which appeared to go completely around the building at the upper floors. And another loud earth-shattering blast with a large fire ball which blew out more debris and at that point everyone began to run north on West Broad Street." (nytimes.com_p5)

"my lieutenant said he looked down at the first floor, and he could see the first floor of the south tower like exploding out" (nytimes.com_p5)

Another firefighter stated "all 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 and my officer just actually took all of us and just threw us down on the ground and kind of just jumped on top of us, laid on top of us. There were rocks falling and all that. The lights were still on at that point and all of a sudden the lights went out and you couldn't see anything." (

NYC firefighter stated "It actually gave at a lower floor, not the floor where the plane hit, because we originally had thought there was like an internal detonation explosives because it went in succession, boom, boom, boom, boom, and then the tower came down." (

Paramedic Daniel Rivera said "At first I thought it was -- do you ever see professional demolition where they set the charges on certain floors and then you hear "Pop, pop, pop, pop, pop"? That's exactly what -- because I thought it was that. When I heard that frigging noise, that's when I saw the building comimg down." (

A facilities manager in the north tower said "There were explosions going off everywhere. I was convinced that there were bombs planted all over the place and someone was sitting at a control panel pushing detonator buttons." (

“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." and later "The ground shook again and we heard another terrible noise and the next thing we knew the south tower was coming down." (nytimes.com_p5)

"Within a short period of time (approximately ¾ of an hour) one of the buildings to the World Trade Center collapsed. During this time period there were numerous explosions, causing us to leave and re-enter the incident area" (nytimes.com_p88)

I was distracted by a large explosion from the south tower and it seemed like fire was shooting out a couple of hundred feet in each direction, then all of a sudden the top of the tower started coming down in a pancake. I remember my jaw dropping and just staring at it and Richard Banaciski, one of the firemen that was there, yelled "Run" and I turned and I started running into the parking garage of the Financial Center."

Q. Bill, just one question. The fire that you saw, where was the fire? Like up at the upper levels where it started collapsing?

A. It appeared somewhere below that. Maybe twenty floors below the impact area of the plane. (

Just maybe about a minute had gone by and somebody said "look the building is starting to bulge." We looked up and you could see the entire facade starting to buckle on the upper floors. Immediately nobody said anything. We just turned and ran as fast as we possibly could. - Dean Beltrami FDNY Company 260 nytimes.com_p4

A NY police officer noted "As we were at the desk we kept hearing explosions that would shake the whole room. People were saying "there's another one and another one" (nytimes.com_p61)

“It sounded like a bomb and the lights went on and off,” said Sanchez. “We started to walk to the exit and a huge ball of fire went through the freight elevator. The hot air from the ball of fire dropped Chino to the floor and my hair got burned,” ... “The room then got full of smoke and I remember saying out loud "I believe it was a bomb that blew up inside the building." (

"I saw what was happening and it sounded as if you had a hundred of those little black cat firecrackers and you lit them off all at once, that's what it sounded like. It sounded like the finale of the 4th of July over the east river." (video_15:12)

I remember seeing, it looked like sparkling around one specific layer of the building. I assume now that that was either windows starting to collapse like tinsel or something. Then the building started to come down. My initial reaction was that this was exactly the way it looks when they show you those implosions on TV. I would have to say for three or four seconds anyway,

maybe longer. I was just watching. It was interesting to watch, but the thing that woke everybody up was the cloud of black material. It reminded me of the 10 commandments when the green clouds come down on the street. The black cloud was coming down faster than the building, so whatever was coming down was going to hit the street and it was pretty far out. You knew it

wasn't coming right down. Judging from where people were jumping before that, this cloud was out much further. -Tom Fitzpatrick FDNY Deputy Commissioner for Administration

Firefighter stated "Meanwhile we were standing there with about five companies and we were just waiting for our assignment and then there was an explosion in the south tower, which according to this map, this explosion just blew out in flames. A lot of guys left at that point. I kept watching. Floor after floor after floor. One floor under another after another and when it hit about the fifth floor, I figured it was a bomb, because it looked like a synchronized deliberate kind of thing. I was there in '93." (

At 8:53am the Police Desk received a report of "an explosion on the lower level" (nytimes.com_p17)

"As more and more and more and more and more emergency vehicles descended on the World Trade Center, I hear a second explosion in WTC 2, then a loud, low-frequency rumble that precipitates the unthinkable -- a collapse of all the floors above the point of explosion. First the top surface, containing the helipad, tips sideways in full view. Then the upper floors fall straight down in a demolition-style implosion, taking all lower floors with it, even those below the point of the explosion."

"I hear another explosion followed by a now all-too familiar rumble that signaled the collapse of WTC 1, the first of the two towers to have been hit. I saw the iconic antenna on this building descend straight down in an implosion twinning the first." (

"it sounded like gunfire... bang bang bang bang bang... and then three big explosions" (video)

I was watching the fire, watching the people jump and hearing a noise and looking up and seeing - it actually looked - the lowest floor of fire in the south tower actually looked like someone had planted explosives around it because the whole bottom I could see -- I could see two sides of it and the other side -- it just looked like that floor blew out. I looked up and you could actually see everything blew out on the one floor. I thought, geez, this looks like an explosion up there, it blew out. Then I guess in some sense of time we looked at it and realized, no, actually it just collapsed. That's what blew out the windows, not that there was an explosion there but that windows blew out. -FDNY Battalion Chief Brian Dixon

I was standing at the south end of China town when the first tower came down. There were more sounds of explosions. They echoed off of the other buildings, perhaps seven or more explosions. The top of the first tower had seemed to twist slightly, as though it was going to fall to one side. I really thought it was going to tumble onto an entire block. However, it went straight down. This was really surprising. -David Long

2011-09-09 - ABC News - 'Real fear': Your September 11 stories (link)

Police Officer described events which occurred inside Tower One after the second plane hit and well before that tower collapsed: "We went back up to the sixth floor . . . . Then there was an eerie silence and it was like you knew something was going to happen. There just seemed to be one explosion after another. I was separated from the guys from the bridge . . . by another explosion, massive again, sucking the air out of your lungs and then just a wind more intense this time with larger pieces of debris flying." (pages 94 & 95) (

(below the impact zone) An incredible noise - he calls it an "exploding sound" - shook the building, and a tornado of hot air and smoke and ceiling tiles and bits of drywall came flying up the stairwell. "In front of me, the wall split from the bottom up," he says. (

"We start walking back there and then heard ground level explosions and I'm like holey shit and then you heard that twisting metal wreckage again." (

Assistant Chief Engineer at the World Trade Center arrived on the 38th floor of the North Tower before the plane hit, got out of the elevator, and about 50 feet down the hallway, he heard a loud explosion and was lifted into the air. "I can't even tell you how far I traveled," he recalled. When he landed, people were already coming out of their offices into the hallway . . .Upon reaching the 43rd floor, "there were patches of ceiling that was just down on the floor, water pipes were broken, water was gushing like a brook or river that was just running down the corridor of the machine room." (

The last person out of the north tower, said that there was a massive explosion in the North Tower before the plane hit. pics/album2/WilliamBush2.html (source) (source) (

Stationary engineer who worked in world trade center one described tremendous damage in the basement of the building more consistent in nature and timing with a bomb than with damage from jet fuel: "'There was nothing there but rubble . . . We're talking about a 50 ton hydraulic press—gone!'. . . They then went to the parking garage, but found that it was also gone. Then on the B level, they found that a steel-and-concrete fire door, which weighed about 300 pounds, was wrinkled up 'like a piece of aluminum foil.' Having seen similar things after the terrorist attack in 1993, [he] was convinced that a bomb had gone off." (

An officer in the New Jersey Fire Police Department who was previously a sergeant in the U.S. Army, said about the south tower: “[I]t sounded like bombs going off. That's when the explosions happened. . . . I knew something was going to happen. . . . It started to get dark, then all of a sudden there was this massive explosion.” Then, discussing her experiences during the collapse of the north tower, she said: “[There was] another explosion. That sent me and the two firefighters down the stairs. . . . I can't tell you how many times I got banged around. Each one of those explosions picked me up and threw me. . . . There was another explosion, and I got thrown with two firefighters out onto the street.” [Women at Ground Zero - Stories of Courage and Compassion (pages 65-66, 68)] (source)

It is known that structural steel begins to soften around 425°C and loses about half of its strength at 650°C.4 This is why steel is stress relieved in this temperature range. But even a 50% loss of strength is still insufficient, by itself, to explain the WTC collapse. It was noted above that the wind load controlled the design allowables. The WTC, on this low-wind day, was likely not stressed more than a third of the design allowable, which is roughly one-fifth of the yield strength of the steel. Even with its strength halved, the steel could still support two to three times the stresses imposed by a 650°C fire.

"anyone who has ever watched a building being demolished on purpose knows that if you're going to do this you have to get at the under-infrastructure of the building to bring it down" -Peter Jennings 09/11/01 (source)

'then the building popped lower than the fire which learned was guess the aviation fuel fell into the pit and whatever floor it fell on heated up really bad and thats why it popped at that floor thats the rumor heard but it seemed like was going oh my god there is secondary device because the way the building popped thought it was an explosion -Timothy Burke FDNY Engine 202

We just kept walking up. As far as we knew, there were no planes or anything coming in. There wasn't even a plane that hit that building. We just knew there was a fire up there. Any other explosions that we felt from inside were maybe extra machinery or something like that. Those were the words that we were getting. -Frank Campagna FDNY Ladder 11

I guess about three minutes later you just heard explosions coming from building two, the south tower. It seemed like it took forever, but there were about ten explosions. At the time I didn't realize what it was. We realized later after talking and finding out that it was the floors collapsing to where the plane had hit. We then realized the building started to come down. At that point everybody at the command post took off into -- there were two garages across. I guess it was by Two World Financial Center next to the Winter Garden, just a little bit south of the north bridge. Everybody took off into an underground garage. -Craig Carlsen FDNY Ladder 8

Q. When the north tower was coming down, did you have any indication? Did you hear the explosions again? Did anybody warn you like they heard on the radio or anything like that?

A. I didn't have a radio, because we were coming from the medical office. So I never did get a radio. So I wouldn't have heard that, if somebody had said it. You did hear the explosions. Of course after the first one -- the first one was pretty much looking at it like in awe. You didn't realize that this was really happening because you kind of just stood there and you didn't really react as fast as you thought you were going to. The second one coming down, you knew the explosions. Now you're very familiar with it. Of course when I looked up, all I could see was the antenna coming down. You pretty much just pick up and take off. Everybody was on their own, I guess.

Q. All right. Thank you, Craig. The time now is 2:04 p.m., and this concludes the interview. -Craig Carlsen FDNY Ladder 8

We put our gear on, started going moving forward, and that's when we heard the rumbling. Somebody screamed, "The building's coming down." I had one shoulder strap on, I dropped my mask and I turned around and made it to -- I tried to run towards the restaurant to get out. I didn't get any more than one step and everything just turned black, and I got pulled into a corner in there that was still standing. My helmet came off. I had a concussion, I believe. That was it. At that point I didn't think I was going to make it out alive. I thought that was it. I made noise at the door. I banged on the door really loud before guys came to me. One guy from 24 Truck was bleeding really bad. He had no face piece on his regulator. I said, "Let's get this door open." I put my light on and I started banging and making a lot of noise. Other guys came and started lifting up the door. I heard a guy from my company screaming, "I've got the way out. It's over here." I followed his voice with two other firemen. I followed his voice. That's pretty much what I remember as far as locations and locations of the companies that I saw that were operating.

Q. Which tower were you operating in?

A. South tower.

Q. South tower.

From there where did you go? Did you go to EMS?

A. I came out. I came out of the crater. The street was gone, the restaurant and everything was gone. I saw Koyles and Vitiello. They were alive. I saw them and then I turned around and I couldn't see them. Walker had come out. I turned around and Koyles was gone. I don't know where he went. I told Vitiello, I said, "Follow me," because he's a proby. Then I turned around and he was gone. He walked another way. I walked up -- by the overpass was a fire truck there. There was a fireman crushed. There was another guy who was screaming, going crazy. I walked another 50 feet and there was another guy that was dead. There were bodies everywhere. I walked another like 50 feet. I was limping. I hurt my knee, my back. My eyes were closing. I couldn't see. I bumped into a guy on the floor. I helped him. He was hurting. He was injured bad. I started walking with him. Another fireman came over and helped me. We just kept walking, and we ended up at the water marina. A boat came over, and they pretty much threw us on the boat. They said, "You guys are banged up. Get on the boat." And that was it. -Gerard Casey Firefighter Second Grade FDNY Ladder 122

"we start walking back there and then i heard a ground level explosion and im like holy shit and then you heard that twisting metal wreckage again" -Jason Charles FDNY EMT Battalion 13

The chief told us, "All right, make your way to the 90th floor in the south tower." I remember Steve started walking right away. I remember I put my arm around Freddie and I said, "Did he say the 90th floor?" Freddie looked at me and said, "Hold on a second." Right as he said that, I heard a loud roar, "boom, boom, boom, boom, boom, boom," and it was getting louder. I looked around, and we were looking at each other. What is that noise? I just looked out the window of the lobby. I could see stuff out of the window of the lobby hitting the street, and I just dove into the corner of the wall. -Lieutenant John Citarella FDNY Hasmat

Joe Angelini and I were out in West Street, and he starts walking towards the hotel. We tried to tell him, "Joe, they want everyone out of here. They think the other one is going to come down." He started walking over. -Lieutenant John Citarella FDNY Hasmat

I turned, I took maybe a couple more steps, and then I heard another explosion, it sounded like. I looked up, and the north tower was starting to come down. -Lieutenant John Citarella FDNY Hasmat

He said, "There is a lot of people gonna be hurt on the outside." He was a policeman so he was all concerned about a secondary device. So he was saying that, you know, he kept drilling that into my head: "Secondary device," "Secondary device," "Secondary device." You know, it's not over. There is something else that's gonna happen. He goes if that first tower came down, he said, this might go down too. -Patrick Connolly FDNY Ladder 16

"I was directly in the middle of the street on washington street and there were two guys three guys behind me and I was right in the middle of the street and thats when the tower started to come I happened to be looking up at it and from the fire floor down it was just like really loud crackling noise it sounded like a million firecrackers and just a wave right from the fire floor down just a wave that started to come down" -Dean Coutsouros FDNY 2nd Grade Engine 220 [htttp://]

"I remember glancing to my right and Joe Mazzarella was at that moment looking up I suddenly saw his face like look of complete terror and he just turned on his heel and took off running I started running after him and looking over my shoulder the tower was - it looked to me - I thought it was exploding actually thats what I thought for hours afterwards that it had exploded or the plane or there had been some device on the plane that had exploded because the debris from the tower had shot out far over our heads it was raining down. " -Fire Marshal John Coyle Brooklyn Base Squad 34

And while I was still in that immediate area, the south tower, 2 World Trade Center, there was what appeared to be at first an explosion. It appeared at the very top, simultaneously from all four sides, materials shot out horizontally. And then there seemed to be a momentary delay before you could see the beginning of the collapse. -Chief Frank Cruthers FDNY Citywide Tour Commander

At that time I started walking back up towards Vesey Street. I heard three explosions, and then we heard like groaning and grinding, and tower two started to come down. -Paramedic Kevin Darnowski FDNY Battalion 20

All of a sudden you heard the rumble and people yelling and screaming. You look and you see -- I didn't see the top of the building. I didn't see the top of tower two. The collapse started. You felt like the ground - it was like a deep sound, rumble; like you're laying on the platform and the D train is coming. You look and you see what - I best describe it as a wave coming. -Lieutenant Rene Davila FDNY Battalion 04

We heard a rumbling noise, and it appeared that that first tower, the south tower, had exploded, the top of it. That's what I saw, what a lot of us saw. -Father John Delendick

I remember asking Ray Downey was it the jet fuel that blew up. He said at that point he thought there were bombs up there because it was too even. As we've since learned, it was the jet fuel that was dropping down that caused all this. But he said it was too even.

Q. Symmetrical?

A. So his original thought was that he thought it was a bomb up there as well. -Father John Delendick

We didn't know the building came down. We just knew the top of the building exploded and didn't know what happened to the rest of the building. -Father John Delendick

It was weird how it started to come down. It looked like it was a timed explosion, but I guess it was just the floors starting to pancake one on top of the other. -Battalion Chief Dominick DeRubbio FDNY Division 8

The next thing I know, we heard a little bit of a rumbling, and then white powder came from the first collapsed building. I thought it was an explosion initially. -George J. DeSimone, Lieutenant FDNY Engine Company 224

I looked up, and the tower started coming down, which at the time I said I thought it was a secondary device. -Lieutenant Robert Dorritie FDNY Engine 53

We were in the process of getting some rigs moved when I turned, as I heard a tremendous roar, explosion, and saw that the first of the two towers was starting to come down.....When the dust started to settle, I headed back down towards the World Trade Center and I guess I came close to arriving at the corner of Vesey and West again where we started to hear the second roar. That was the north tower now coming down. I should say that people in the street and myself included thought that the roar was so loud that the explosive - bombs were going off inside the building. Obviously we were later proved wrong..... As I said I thought the terrorists planted explosives somewhere in the building. That's how loud it was, crackling explosive, a wall. -Assistant Commissioner James Drury FDNY

We proceeded through a broken window that the Fire Department broke to lead access into the south tower. We proceeded to set up a triage area. At that time plans changed and we transferred the triage area over to 7 World Trade Center, in the lobby. -Gregg Brady Battalion 4, EMT nytimes.com_p4

At that time, I had a very tight feeling in my stomach, just experiencing what I went through with 2 World Trade Center, being that close. I didn't feel at ease at all. We were standing underneath and Captain Stone was speaking again. We heard -- I heard 3 loud explosions. I look up and the north tower is coming down now, 1 World Trade Center.... At that time, when I heard the 3 loud explosions, I started running west on Vesey Street towards the water. At that time, I couldn't run fast enough. The debris caught up with me, knocked my helmet off. I tumbled and then eventually I started running again. -Gregg Brady Battalion 4, EMT nytimes.com_p7

We just took our tanks off and our jackets off, and that's when the second building came down. It came down right behind us. So now we started running down West Street towards Stuyvesant High School. Take a peek behind. You could see this black cloud coming behind you. You couldn't out run it, and you get caught in that black, and I felt like the push, you know, from this black cloud, and I got myself to the first building before Stuyvesant High School, and I seen guys go inside there, and I made the turn around the building, and I went inside that building, because, I mean, you couldn't see your hand in front of your face. -Firefighter Peter Fallucca FDNY Engine 16

When I was going -- that was when they gave the order to get out. I was on my way down. I don't know what floor I was on when I heard it, but it was fairly high. Had to be like in the high teens, maybe 20th Floor, just as I was starting to go down. They were telling us to go down, and I heard Rescue 1 say to meet up, all rescue one members meet up on the 40th Floor, and I know all those guys are no longer with us any more, so they were somewhere headed to the 40th Floor, I would imagine, those guys.

Q. As far as --

A. I heard Maydays given for guys -- guys -- I heard of guys passing out. Still missing members I heard. This is before anything had collapsed.

Q. Can you remember any specifics, any specific companies?

A. No, I remember hearing that they found the boss from Engine 1. I remember hearing, found an officer from Engine 1, possibly DOA. I remember hearing that on the radio, but the only real one I can remember where guys were going was Rescue 1. I heard them say meet up on the 40th Floor. I heard that transmission for Rescue 1.

Q. And the highest floor that your company, Engine 16 got to, was the 23rd?

A. 23rd Floor. And we were going to go higher, but at that time they had ordered us out, and we went down.

-Firefighter Peter Fallucca FDNY Engine 16

I heard the explosion, looked up, and saw like three floors explode, saw the antenna coming down, and turned around and ran north. -Firefighter 1stKevin Gorman FDNY Ladder 22

Q. Any particular event that stands out in your mind for -- or struck you as odd or anything like that?

A. Just actually the collapse and the sound it made. It was like a strange sound, rumbling, not the loudest thing you ever heard, not like a boom explosion type thing, but just strange. How fast it was collapsing, you just started running. -Lieutenant Gregg Hadala FDNY EMS Battalion 50

A large explosion took place. In my estimation that was the tower coming down, but at that time I did not know what that was. I thought some type of bomb had gone off. -Lieutenant Gregg Hansson FDNY Engine 24

We came out from 90 west made a left headed east and riqht when we qot to the corner of washinqton and albany thats when I heard the building collapse first I thought it was an explosion I thought maybe there was bomb on the plane but delayed type of thing you know secondary device

Q. I was convinced for week it was secondary devices -Battalion Chief Art Lakiotes

A. You know and I just heard like an explosion and a then a cracking type of noise and then it sounded like a freight train rumbling and picking up speed and I remember I looked up and I saw it coming and I was able to make it across Washington to the very corner of Washington and Albany I think its the south side of Bankers Trust Building. I made it right to the corner and there's a column right there and I was with my guys we all made it to like the column and I remember it was plate glass behind me and im thinking im going to get hit by this glass and like a porcupine im going to get it you know but nonetheless it rumbled it was the loudest rumbling I ever heard the ground shook and I got thrown down and I remember it just got black and I got knocked down I remember being buried I think I ducked more or less you know pieces of metal something hit me not that heavy though wasnt an I beam or else I wouldnt be talking to you and I remember that being on me and I kind of was able to stand up and push everything off me but I now felt like I was in the street or the sidewalk and it was hot smoky I felt like I was in a fire and I remember digging my way out a lot of cementation powdery insulation whatever you want to call it almost like being in a blizzard with some metal debris right on me fortunately nothing heavy hit me. -Timothy Julian FDNY Ladder 118

"As we were walking we heard we thought it was another plane coming it was like a big shhhhh a thousand times louder than that it sounded like a missile coming and we just started booking we took off like bats out of hell we made it around the corner and thats when that shit hit the fan right then and there we heard that loud and then ba boom I just it was like an earthquake or whatever a giant giant explosion Kenny made it and those other guys made it around this bend here I was like the last guy and I just turned around and I just sort of ffffffff I just did fetal position I crawled down and held thank god that helmet saved my life I just held onto it and the impact I closed my eyes just the impact I could just feel shit hitting me flying. I think something fell on my back that protected me from some of the other stuff that fell luckily a couple of things hit my helmet then it was just that impact and I was in a fetal position just holding my helmet shaking then this big gust came and I just went flying maybe 30 40 feet tumbling. I got up got on my hands and knees because all of the white shit was all over me I just kept crawling my ears were like deaf you know when you hear a giant firecracker or something -George Kozlowski FDNY Ladder 20"

"...our attention was drawn to the south tower. There was some kind of explosion, you might say, up in the area where the fire was. Actually, in hindsight, that was the start of the collapse." -Dave Lynn Supervising Fire Marshal, Brooklyn Bureau of Fire Investigation

"Then all of a sudden there was like a loud - almost like a rushing sound, a roar, and we looked up and we could see it looked like an implosion and the building kind of went in and out and kind of like shook. -Captain David Loper FDNY Engine 210

"The ground shook again and we heard another terrible noise and the next think we knew the second tower was coming down." -Lieutenant Bradley Mann FDNY

"In that process of him trying to explain to me to pull my ambulance over, I heard a loud bang. We looked up, and we just saw the building starting to collapse. I looked over and started to scream at my partner, which he was inside the vehicle. .... I was screaming from the top of my lungs, and I must have been about ten feet away from her and she couldn't even hear me, because the building was so loud, the explosion, that she couldn't even hear me." -Julio Marrero FDNY EMT

"I was talking to him when I heard loud like a roaring noise like a loud loud roaring noise at the time I didnt know what it was I just looked up all I could see because of the fog that was there you couldnt see above your distance was limited once I heard that I heard like a big explosion a tremendous explosion let me put it that way and rumbling sound" -Edward Martinez FDNY EMT

"All of a sudden I heard this huge explosion, I didn’t know what it was cause nobody was telling me anything. I didn’t know until we were called back to Chambers and something, Chambers and West Street, that it might have been a terrorist attack. I was this close to it, and I didn’t know what was going on. After that I heard this huge explosion, I thought it was a boiler exploding or something." -James McKinley, FDNY EMTD Battalion 8

"It tipped down first and then the thing fell within itself. It was an amazing sight to see. It was really unbelievable. I thought I was watching a movie with special effects." -Michael Mejias FDNY EMT

"As we are looking up at the building, what I saw was, it looked like the building was blowing out on all four sides. We actually heard the pops. Didn't realize it was the falling -- you know, you heard the pops of the building. You thought it was just blowing out." -Joseph Meola FDNY

"VON ESSEN: That's the building they were worried about collapsing.

KING: That one?

VON ESSEN: Yeah, (UNINTELLIGIBLE). It's got a little bit of a (UNINTELLIGIBLE) on the top, so people thought it was going to collapse. And in the first day or two, there was a lot of panic going on, because we didn't know. Now we have a handle on it, but the first day or two, they didn't know if there were secondary devices in other buildings, people were running, you know, very afraid."

CNN Interview with Thomas von Essen, N.Y. Fire Commissioner; aired October 6, 2001

"I was thinking ‘okay, great, we’re safe’. But outside I could see all this falling debris flying around. I thought ‘we’ve being coming down for an hour, what the hell is this’.” By now, he had been paired with Ruth, who had sprained her ankle and had trouble getting down. They were ordered down to the lobby floor and directed across the plaza to an exit on the eastern side of the complex, Steve helping Ruth along under the drenching rain of the fire sprinklers. Seconds later, at 9.58, Two World Trade Center imploded. We were about 50 feet from the escalator up to Church St and I was saying to Ruth ‘we’re okay, we get up this escalator and we’re okay’, and then there was a big rumble and a huge roar and everybody shouted ‘run’ and then a huge wind came through there. I remember distinctly being lifted off my feet and blown down the hall, I don’t know how far. Ruth was holding onto me but we were ripped apart. I had no conception of what was happening. It went through my mind that a bomb had gone off in the subway. Then the plume came through and there was an opaque blackness. It was not an absence of light. It was opaque. My glasses were gone. I put my hand in front of my face and I couldn’t see it. I thought ‘a bomb has gone off and I’m going to die right here of smoke inhalation’. Then I realized that it wasn’t smoke, that it was just very heavy air. There was all this stuff on the floor but it was light stuff. I was coated in it, as if I’d been immersed in a vat of butter. And the exposed skin on my arm was all pocked from tiny glass shards, maybe 100 of them."

2001-09-17 - American Bureau of Shipping - Cheating death (Lloyds List) (link)

2001-09-12 - Berlingske Media - Tonsvis af sprængstof (link) FBI Believed that Bombs Were Used on 9/11

A leading collapse expert thought the South Tower was brought down with explosives:

9/11/2001: USA Today Reveals FBI Theory That World Trade Center Towers Destroyed By Explosives:

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