If the exterior stair serves a required exit then these stairs are considered a “fire escape” and need to apply all the requirements as mentioned in 184.108.40.206.
If the exterior stairs does not serve a required exit then you don’t apply any of the requirements in 220.127.116.11. That all you have to worry about.
The requirement for protection of openings on the building wall is to prevent a fire from breaking through the openings and preventing occupants from exiting via the fire escape. If this is not a fire escape because it does not serve a required exit there is no need for protection according to the code because it’s not a required exit, technically it can be blocked off.
I’m not sure why Rob above is asking you to obtain an engineer’s report for the exterior wall. Why would a wall have a fire resistance rating and furthermore this has nothing to do with the subject matter, it’s not applicable. We don’t even have the right to ask for an engineers report, what reference you are going to use? Also a fire escape is permitted to be installed under 18.104.22.168.;we are not enforcing the OBC on a new building, that’s the Building Department.