When Chernobyl 'sprung a leak' I was at
university at
Aberdeen (in
Scotland). Some high ups in one of the departments decided to take one of their
geiger counters outside the department and check the
radiation levels (Aberdeen is called the granite city and the background is about 4x UK norm).
When they got out they switched on the detector and the needle nailed itself to the top of the meter. It was not until they were back inside (a transition that occurred very quickly indeed) that they noticed they had not a Geiger-Muller tube (for detecting radioactive particles) in the detector but a scintillation detector which counts very weak light pulses (which they had pointed at the sky).
History does not record exactly how stupid they felt.