Continuity mistake: When Dan dies there's a wide shot of the building with several floors engulfed in flames. When Lorrie is free-falling just two seconds later, for the scenes play in real time - the flames have disappeared. (01:04:53 - 01:06:10)
Revealing mistake: When Lorrie jumps out of the window, she is replaced by an obvious stuntman: Fireproof gloves appear on her hands, she is wearing a fireproof mask, and her hair is an obvious wig.
Deliberate mistake: For the sake of the movie's plot and tempo, all the guests manage to breathe and stroll around quite calmly for several minutes despite the heavy smoke, when in real life they would be blinded and choking.
Factual error: When the fire department first arrived, they should have had the utility provider shut off the gas lines to avoid just the type of explosions that happened continually throughout the movie.
Continuity mistake: When the elevator is lowering the people, a wide shot shows the building on fire. Couple shots later the flames are nowhere to be seen.
Continuity mistake: When the floor explodes and the elevator breaks, a woman in pink crouches. Shot changes and she is standing tall again.
Continuity mistake: When Roberts hands Duncan the scorched wire, the way Duncan holds it differs between the wide and the close-up shots.
Plot hole: By the time O'Halloran phones Roberts, who is in the promenade room, and tells him of their plan to blow the water tanks, over 50 of the floors below the promenade room, along with the roof which is also ablaze, have been destroyed by the fire. So surely the phone lines would have been destroyed as well, making a phone call to the promenade room impossible.
Revealing mistake: After Dan Bigelow is killed, Lorrie goes back into the office to protect herself from the flames. When she is kneeling down in the office, you can see the fireproof pants on her legs. (01:05:00)
Continuity mistake: When Doug first arrives at the Tower, he goes down an elevator from the roof to the 65th floor, then has to cross over to different elevators. In one of these, he goes up - to 79 according to the display; but the floor buttons on the control, consist of just 16 buttons; the 7th or 8th button is lit as he gets off, so he has only gone up halfway to 79. (00:06:45)
Continuity mistake: When the first woman goes across on the breeches buoy, the overhead shot of her going across does not show the outside elevator which at this stage is hanging by a cable and stuck on the outside. However, it is visible in the shots from the peerless building which the breeches buoy is attached to. (02:05:10)
Revealing mistake: During the party, doors open and a burning man appears. He is wearing fireproof gloves, his face is covered in some dark mask and some sort of awful wig to hide all the safety procedures. He resembles a werewolf. (00:57:20)
Audio problem: When Lorrie jumps out of the window, she yells out loud and clear, but her stunt is firmly covering her mouth.
Character mistake: When Steve McQueen arrives at the fire scene, he drives his car across a fire hose. It is basic firefighter training that you NEVER drive a vehicle across a fire hose.
Continuity mistake: The light outside the building as seen from the dining hall is dusk, but from the outside it's pitch dark. This swaps back and forth all the time.
Continuity mistake: At Patty's place, she places her right arm next to her face holding a cracker. Shot changes to a side angle and her arm is lowered. Then a shot afterwards it's raised again.
Continuity mistake: A technician talks to Mr. Callahan and leaves. Callahan places both hands on the computer, but a shot later his left arm is lowered. (00:11:42)
Continuity mistake: The art teacher cleans her hands with a towel, but a shot later they're lowered. (00:10:49)
Visible crew/equipment: When Harlee arrives at the building, set lights are reflected on his sunglasses.
Continuity mistake: The people inside the elevator disappear in the wide angle. (01:57:21 - 01:57:51)
Answer: Where the stairs were blown out they could have crossed over to the adjacent stairwell and back.