As part of my teaching course I was given some case studies of accidents and incidents in school science labs. My Favourite is this one:
A teacher was demonstrating the high voltage transmission line as follows. An ac power supply, set at about 14 V, was connected to a step-up transformer, resulting in an output of about 240 V. This supply was connected by crocodile clips to bare parallel wires held along the length of a metre rule. at the other end of the wires was a step down transformer and suitable lamp. The teacher wanted to show the effect of varying the length of wire on the brightness of the bulb. She took hold of both crocodile clips, forgetting they were live at about mains voltage. She was unable to let go.....