I’m confused about this whole discussion
I’m not sure why you’d have to be alone in the office with him with nobody about to arrive
the bottom line is
We have a shulchan aruch their is no need to add your own rules. Their are English guidebooks that can help as well I believe R’ Ribiat has one.
If working there will violate hilchos yichud then it is assur. IF it wont then it isnt.
What am I missing? As far as the specifics of this case, Not nearly enough details are provided. who else works there? who has access to enter? Are the doors locked? Are staff/patients always arriving? etc etc