Stephen Viola

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]