I remember about 1979 when I caught a frantic call from Ops at Aberdeen. Outside was a Puma on spot 4 with its rotors slowly turning. Some engineer had turned the engine for some check and had moved the starter switch from the OFF, through the VENT, to the START position. The engine had fired up and they didn't know how to stop it.
I strolled over to the aircraft and suggested that they put the switch to the OFF position.
The wonders of modern science.