The weekend shifts at the control room of a bit of national infrastructure did not know that the indicator light on the wall meant diesel generator active. It worked really well, so well they didn't notice any difference. Until it used up its tank of diesel.
Apparently you can't just call the AA to get an emergency fill up. The fuel has a special biocide blended in as it night be sat around for months. Somehow Business Continuity managed to get the Army which had a tanker of the stuff on standby.