There were 3 stairwells in each building. Here's an excerpt from this fascinating wikipedia page[1] about one of the only four people to make it out from above

There were 3 stairwells in each building. Here's an excerpt from this fascinating wikipedia page[1] about one of the only four people to make it out from above the impact in the South tower: "The airliner that struck the North Tower struck it perpendicular to the north face. The impact severed all the elevators and all three stairwells. The airliner that struck the South Tower struck at an angle, severing two stairwells, but it left Stairway A, the one they were using, more or less intact." [1] https://en.wikipedia.org/wiki/Brian_Clark_(September_11_survivor) https://en.wikipedia.org/wiki/Brian_Clark_(September_11_surv...