Comment by jaclaz | Hacker News Reader

Comment by jaclaz | Hacker News Reader

Part of the reasons while AC can be lethal even at lower voltages (110/220) is that the frequency (50/60 Hz) is near to that of the heartbeat and could create a sort of resonance stopping the heart.

Or at least, many years ago it was compulsory in mines and tunnel digging to have a sort of frequency elevator (at the time it was a generator (alternator) with output still at 220 V but with a very high number of Hertz, if I recall correctly 200-600, driven by an electric motor).

They looked more or less like:

https://bullseyeindustrialsales.com/giordano-colombo-c3ll-10...

From a given point in the tunnel (some 150 or 200 meters before the digging point) all cables/lightings were powered with this high frequency line, the idea being that if the cables were damaged in the works and a worker came accidentally in contact with a naked conductor he/she would get a (painful) shock but not risk life.

My understanding is that it's not anything to do with the resonance of a heartbeat or anything like that. The higher frequency ac will experience much more of a skin effect and not penetrate into the body as much or as easily. That means there will be less current that will pass through the organs and heart, but more through your skin and outer muscles. That'll mean it'll hurt more but be more likely to be survivable since you'll have more time to remove the person from the power source.

Most probably that is another part of the story, however it seems like there is the need of more current at higher frequencies:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/197300...

Look around page 40.

I was reporting what I was told at the time, anyway here is a chapter of an electricity textbook confirming (for what is worth) the added danger of low (50-60 Hz) frequency AC current:

https://www.allaboutcircuits.com/textbook/direct-current/chp...

Interesting, I wonder if the higher frequency ends up needing more current because the body can't respond as fast, acting like a filter because the muscles can only move so fast. Biology and electricity mix in interesting ways.

> the frequency (50/60 Hz) is near to that of the heartbeat

This doesn't smell right- if your heart's beating at even 5Hz, that's a whopping 300BPM.

I expressed myself incorrectly, I meant it is a multiple/resonance value, I cannot correct my previous post, unfortunately.

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