There was this one time ......
I was manager on call and the London NHS trust I worked for was in a partnership with two other much larger NHS trusts.
We had premises in one of the other trusts' campuses.
There was a saturday morning generator test which caused a switch to latch. That switch (theirs, not ours) serviced the door access controllers for our floor in their building.
None of the doors would respond to swipe cards. Every door had a 500 kg pull force maglock. Some doors had emergency overrides that cut the power to the mag locks (the terms "fail safe", "fail secure" and "fail open" are all relevant here) Rooms that didn't normally have human occupants were typically 'fail secure'. Everything that could be poked to gain access was on the secure side of the door.
To fix the issue, the switch needed to be rebooted or replaced. However the switch was on a UPS which was on a generator backed circuit that also fed critical stuff that could not be shut off by yanking the power.
The latching event happened at around midday and my on-call engineer had attended site then and was released because we could not fix it and there was nothing he could do.
The situation was resolved at 6pm by representatives from each affected trust - i.e. all 3 trusts - attending to secure their own equipment whilst a man with an axe fought his way through a fat, hefty, fire door.
Switch had power yanked and replaced, booted normally. My guy took some photos to show that our kit was not affected and everyone else went home, leaving the estates people for that Trust to reinstate some sort of door.
Moral of the story is to plan your infrastructure so that you have a way to release imnportant doors - using a key switch above the ceiling tiles that requests a door release (thats logged by the controller) and lets the doors be opened and closed again afterwards.