No sure way out
In high-rise buildings, the stairways are the only emergency means of escape. Even if there are multiple stairways, they are often close together so that damage to one is likely to affect the other. It is also notable that many apartments in buildings, built in New York City since 1960's, have only a single exit. When fire, smoke, fumes or debris block the exit, there is no other way out.
The lack of adequate egress is a significant problem whose magnitude is now beginning to be appreciated. In New York City alone, about one million people live above the seventh floor and cannot be reached by fire ladders. About 1.5 million people work in offices above the 10th floor.