Why the downvotes? Somebody has to design these things, and the voltage they run at must be a consideration. Asking about the design tradeoffs is totally legitimate.

@Olin Lathrop Well... nobody has to design them. Engineers with some sort of moral code might refuse to do so. But I agree that questions regarding why a certain voltage is used by certain electrical equipment are on-topic here.

As for why a certain voltage is used... the aim of an electric chair isn't to burn someone to crisp by making their whole body a conductor for high current, that would be extremely unethical and similar to burning someone alive.

As for your grandfather's story, it sounds like hogwash. For something to actually catch fire, you would need several Ampere running through it. The resistance of the human body + clothes, shoes (likely rubber) etc + the ground itself, is many Megaohms. So even if someone manages to charge their body to a potential that is 700kV higher than ground, they would never realistically discharge that voltage with high enough current to make something catch fire.

Are there any considerations from electrical perspective, such as safety regulations - I don't think safety is a consideration if the object of the exercise is to shuffle off someone's mortal coil.

@Lundin: The catching fire part was probably the visual effect of arcing. When the worker jumped out of the truck, he was probably still nearly touching it when he also touched the ground. This greatly reduced the insulating clearance, due to the body being essentially a conductor. The 700 kV jumped the remaining gaps, ionizing the air. The 700 kV now across the body caused rapid heating, boiling, and steam explosion. This can look like "Instantly combusting" to untrained observers.

@Olin Lathrop Maybe he was rather holding on to a metal truck chassis shorted to 700kV while touching the ground with another body part. Though I suppose you need quite a big clearance distance for 700kV, several meters perhaps.

@Andy aka I think usually witnesses are required. I was thinking that perhaps some regulation forbids being near/in the same room with certain exposed conductors that are high voltage or such. Perhaps some other aspects as well

@Olin Lathrop What do you think about 'Step Potential' in that worker scenario? . Just a guess.