This photo on the left shows the prototype building. Close examination of this and other photos shows that the stairs are the open frame type with a mesh type screen over the railing.
This photo shows my model of the building as it is now, without the stairway. The highlighted area is where the stairway will be added. I need to match the existing building tile.
Plastruct makes a line of products in N and HO scales to model industrial stairway. I've used these before and would use them for the basis of this project.
Here is what I have so far. I started with a .020 sheet of styrene. Then I laminated the tiled styrene over that with gaps where the doors would be. Except for the bottom and top flights, all the stairs are in. The Plastruct railings are used for the inside and .020 x .250 styrene strip for the outside as seen between floors 2 and 3.
I'll make another post on this in the future showing how it came out when it's done and attached to the building.