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Electric shock pulse duration vs current vs lethality
Manul:
--- Quote from: T3sl4co1l on February 26, 2021, 04:56:44 pm ---In addition to the above, the body acts as a lossy filter -- or at least, it should. If the pulse is well balanced (AC), the effect is mainly heating. If unbalanced (like an electrostatic spark), all the high frequency AC content again is filtered out (and absorbed as heat), however the DC component still develops a voltage drop across membranes, causing electrolytic transport, ionic movement, depolarization, all that.
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This was something I was thinking about. If a pulse is unipolar, like an ESD event, it might be filtered by the body and streched in time and because of that go more deep. HBM ESD of 10 kilovolts already feels nasty. It might be just a few 10's of nanosecods in duration, but certainly feels like going through the muscles.
I worked once with a radar system with a 30kV TWT. I think that would be an instant death, no question. I also worked with a few s and x-band pulsed (magnetron) radars and the modulator output is in the range of kilovolts with a duration 50ns - 1us and PRF of a few kHz. Pulse is more or less rectangular. I assumed the worst and worked with maximum safety precautions, but I was wondering, would it be death or just a nasty shock if some horrible mistake happened. There is a saying, that sometimes a gun without bullets may shoot. Thankfully, I work rarely with such high voltage stuff. Honestly, I don't like it, gives me nerves.
Out of curiosity I tried to search about the lethality of pulses. What I found is that studies seem to not involve such short pulses, ether single or repetitive. There is lots of information about DC and low frequency AC though.
T3sl4co1l:
Heh... well the TWT if that was continuous collector voltage, you don't stand a chance, those capacitors will discharge a lot longer than 50ns. :-DD
Radar systems are surprisingly comparable in power output, at least the smaller ones (airborne, maybe ATC, not sure?) -- ~100kW range. If you got near the pulsed end, dunno, can't say I'd recommend it, especially in the longer pulse durations -- but the shorter pulses might not feel like much, or relatively small zaps, being on the order of EFT or ESD.
Also, there are numerous stories of Army grunts (and others) sitting some distance in front of the radar on a cold winter's day, to keep warm... can't say I'd recommend that either, but if it's not nuking your eyeballs or nuts, and it's not melting your skin off, just more of a pleasant warmth despite the crest factor -- yeah, might as well I guess. :o
Tim
Manul:
--- Quote from: T3sl4co1l on February 26, 2021, 11:47:50 pm ---Heh... well the TWT if that was continuous collector voltage, you don't stand a chance, those capacitors will discharge a lot longer than 50ns. :-DD
Radar systems are surprisingly comparable in power output, at least the smaller ones (airborne, maybe ATC, not sure?) -- ~100kW range. If you got near the pulsed end, dunno, can't say I'd recommend it, especially in the longer pulse durations -- but the shorter pulses might not feel like much, or relatively small zaps, being on the order of EFT or ESD.
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I think there was a few microfarads of output capacitance at TWT supply and the output rated at something like 50kW continuous. The pulsed ones were around 25kW pulse and around 30W average power. I was running them with a waveguide dummy load and a little fan attached, it was not getting very hot. But high voltage pulses to the magnetron, I dont know how that would feel. I was doing pulse length and shape adjusting, so had the modulator open and the probing hooked up.
--- Quote from: T3sl4co1l on February 26, 2021, 11:47:50 pm ---Also, there are numerous stories of Army grunts (and others) sitting some distance in front of the radar on a cold winter's day, to keep warm... can't say I'd recommend that either, but if it's not nuking your eyeballs or nuts, and it's not melting your skin off, just more of a pleasant warmth despite the crest factor -- yeah, might as well I guess. :o
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That's cool, but I dont understand where the antenna was mounted and what direction it was transmitting that people could sit in front :) But I'm sure it happened, because people are good to find solutions :)
Someone:
--- Quote from: T3sl4co1l on February 26, 2021, 04:56:44 pm ---There may be studies about how much charge, at what rate, is necessary to do those things. I think the response is not quite a constant-charge asymptote, for short pulses? That is, say you discharge a capacitor of given value and voltage, through 100 ohms, or 1k, or 10k, etc.; the same charge is delivered, but at different rates. For rates faster than the body's filtering time constant, the effect should be ~independent of rate (so maybe 100 ohms feels the same as 1k, but 10k and up feels weaker and weaker).
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IEC 61010 is one reference for safety voltage vs capacitance curves. I believe they assume a "single" pulse event.
--- Quote from: Manul on February 26, 2021, 09:20:07 pm ---Out of curiosity I tried to search about the lethality of pulses. What I found is that studies seem to not involve such short pulses, ether single or repetitive. There is lots of information about DC and low frequency AC though.
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Unlike lasers/optical exposures where repetitive sources are better characterised, its a bit of a missing gap in the electrical standards. Just play it safe and use the worst case 100% duty DC or AC, whichever gives the lower limit. (RF burns are another thing altogether because of their different propagation)
amyk:
Related previous discussion: https://www.eevblog.com/forum/chat/whats-the-current-of-a-static-shock/
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