I spent more than a little time at DHS, talking with my peers and
colleagues in their mainframe systems programming group. This was before
anyone in state government was on the Internet (we were first, and that's
another story to be told in its proper place), and before electronic mail
came to state government here.
One day I was in their machine room, watching them perform a particularly tricky piece of maintenance on some hardware. Their UPS maintenance man went through the door into the UPS room.
A few seconds later, there was a BOOM!, he was blown through the (closed) door, and the lights went off. So did the very large mainframe computers, their attached displays, the long arrays of disk drives and controllers, the printers, the tape drives, and everything else.
We later found out what had happened.
The UPS maintenance man went into the UPS room to take meter readings and to make adjustments if any turned out to be needed. He was carrying a large covered clipboard, made of aluminum.
He put the clipboard on the cover of the rack containing the UPS -- or thought he did. That UPS had no cover over the equipmentL it was all exposed to whatever fell on it from above. In this case, it was that aluminum -- highly conductive -- clipboard which fell right across all three phases of the 3-phase 480 VAC input to the UPS. The clipboard, and some of the wiring, turned to vapor, and the resultant blast wave did in fact blow him through the inward-opening door.
The machine room was back online the next day, after new wiring was run from the input circuit breaker to the UPS.