I worked through TWO total data center blackouts with 1000s of computers. One was caused by the weather where snow smothered the backup generator and one human error by an electrician. The first outage happened around 7 AM. I recovered the last system to come up at 5 AM. Surprisingly few hardware problems after system crashes. The tricky part was restarting systems in the proper order due to NFS dependencies. I always hated NIS and NFS.
I worked in a refinery years ago. The plant had to be shut down for some major repairs. Takes days to shut one down then the start up process takes a while also. All it takes is one thing done out of order and you have a huge mess on your hands.