Power failure is a best case. I've observed firsthand cases of "badge access system went down, none of the doors open". That's less of a problem for external doors that allow people out but not in, because it can be solved by propping the door and posting a guard who checks badges. It's a massive problem when conference rooms and offices lock people in.
there is also the earthquake issue where interior doors (badge access or no) can become jammed. thus god invented the crowbar. my Big Company emergency response team folks all had one. also good for head crabs.