I have a customer placing mezuzot on his office building. One of the doors is an emergency exit which can only be utilized as a fire escape and leads out to the front sidewalk. Normally, such a door would be considered an entrance into the building, and the proper place to affix the mezuzah would be on the right as one is coming in from the street.
There is one caveat, however. From the outside the solid door has no handles and no key! That is, even if one wanted to use it as an entrance into the building, it would be impossible to do so. Would the user of such an office building be exempt on this doorway?