Already there!
Peter is right. :)
Just make sure the group the staff member is assigned to has access to all desired departments.
1. Create or manage a "User Group" that can access to multiple department by selecting them from "Dept Access" direction in "Admin Panel" -> "Staff" -> "User Groups".
2. Assign your staff to that "User Group", afterwards, you will see that this staff can access accross those multiple department.
3. By using this way, you don't have to create separate logins for the same real person staff in order to access multiple department.
Sincerely,
Masino Sinaga