I wasn't too comfortable climbing the stairs with them being open to where you can see below. Is there a reason they would be open and not a solid stair? The only thing I can think of is a weight savings due to an open stair would weigh less than a solid stair.
My guess is light. More natural light can be utilized through open stairs. Solid stairs would block the light from passing to other parts of the tower.
Now that the topic has come up, here's food for thought. Think about the lights you have visited with solid stairs. Did they have small windows in the sides for some natural light? Then think about the lights you have visited with open stair cases. Were there any windows in the sides for natural lighting?
Open stairs are easier to sweep because everything falls to the bottom. That isn't the case with solid stairs.
Interesting thought provoking topic...
Bob
