Establish a codename that you and your coworkers can use for this situation
Install a panic alarm, if possible.
Respond
If the situation is life-threatening, leave immediately and call 9-1-1
If the situation is non-life-threatening, tell the unwanted person that you are calling someone who can help them and call a colleague who cannot be seen or heard by the unwanted person
On the phone, tell your colleague to find Dean/Doctor/Mr./Mrs. [codename]
This codename should be memorized. The colleague to whom you say [codename] should immediately call 9-1-1 and explain the situation (including building, floor number and room number)
Try to stay on the phone if safe to do so
Activate panic alarm if area is equipped with one.
If you are experiencing a life-threatening emergency, please call 9-1-1 immediately.