tl;dr UPS maintenance was performed by a vendor the day before the fire. Fire department used a thermal camera to isolate source of fire, it seemed to originate with 2 UPSes, one of which was the recently maintained UPS
They're building 2500 servers per week.
For the offline buildings that are not destroyed, they have to rebuild the electrical distribution and network. It was not clear if they are also moving servers physically.
The idea of the tower design is to take ambient air in through the outside walls, through I think just one row of servers, then into a central void where convection pulls the air out.
Back when I worked in hosting we'd get an email from this particular DC's NOC about either "UPS Maintenance" or generator testing. Our hearts would sink because, during one particular eighteen month period, there was a 50/50 chance our suite would go dark afterwards.