A friend of mine had done extensive SCADA work at a plant that makes pies, basically the entire process is automated. The SCADA software that we use actually has a Recipe modules for mixing ingredients together. We of course don't need that.
During our change over, the contractor that was working with us, neglected to actually save a changed program to the PLC. That night, we had a thunderstorm and had a major power flicker in the building, the PLC lost power and forgot its programming. We didn't realize that was the problem and it took several hours to figure out what was wrong, because the PLC appeared to be ok. By the time we got it figured out, since the contractor was no longer on site and it was left up to us to fumble through it, the screens had clogged up and the inbound flow had filled a 48" pipe to 44", for the entire 8 mile run of the pipe. We had about another 30 minutes before it would have backed up to the point of popping manholes along it's length.