Electric shock pulse duration vs current vs lethality - Page 1
Forum section: electronics / general

author: Manul
author_rank: Super Contributor
timestamp: February 26, 2021, 02:16:50 pm
content: I'm interested in lethality of very short current pulses. I was not able to find a trustful graph of pulse durations in the range of nanoseconds up to microseconds vs current vs lethality. I understand, that it would be just a rough approximation, because there are so many factors involved, but still better then nothing. Is there a graph of safe area for these durations? Like for example 10ns, 5A - safe. What current would be objectively safe for 1 microsecond? Does it make sense to think in energy therms (joules) for such short pulses? At short pulse durations skin effect must be significant.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 26, 2021, 03:02:24 pm
content: I think you need to define whether you are asking about a physiologic response (e.g., depolarization of a neuron without destruction) versus something more akin to an explosion where death results from something other than a physiologic response. In the latter, I suspect the minimal pulse would be quite short. This study (https://www.nature.com/articles/s41598-018-26521-2) was able to demonstrate myocyte damage with pulses down to 200 ns.In the former, it is more likely a millisecond or two. That is, comparable to the minimal depolarization time for neurons.What are you trying to accomplish?

author: Manul
author_rank: Super Contributor
timestamp: February 26, 2021, 03:48:03 pm
content: Quote from: jpanhalt on February 26, 2021, 03:02:24 pmI'm talking specifically about the failure of heart and the resulting death. Not sure what is the accurate term for this. It is not about burning of skin or single cell damage. For example, high power RF is burning fingers, thats is not involved in the question. There is nothing I try to accomplish. I just want to increase my knowledge and also I believe this information could be useful for others. I was working with devices producing a few kilovolt pulses at around microsecond duration and while I always kept precautions, I always wondered how lethal it actually is.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 26, 2021, 04:27:12 pm
content: If you are concerned about depolarizing nerves and/or myocytes of the heartwithout permanent damage, then I suspect the physiologic process will dominate and the minimal time for that is about a millisecond or two or a little longer. There are numerous reliable sources that show the timing of that process. Here's a simplified illustration:https://faculty.washington.edu/chudler/ap.htmlPermanent damage, of course, doesn't necessarily mean death. Failure to function after such damage will depend on its extent.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 26, 2021, 04:56:44 pm
content: 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. Case in point, you don't feel the streamers from a Tesla coil (give or take intensity, largely because of heating AFAIK), but an ESD spark is quite a lively experience.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).The filtering effect itself, is probably not a dominant-pole effect (i.e. that would give a simple asymptote like the above), but probably more like diffusion, i.e. dependent on sqrt(pulse width) or something like that. Which in turn arises from current flow through a resistive bulk medium. In other words, skin effect, yup. That would be a physical explanation for it, anyway.Anyway, studies are what you're looking for, to put numbers on those general ideas. I think pulses of some ms have been measured, though I forget if µs too?To clarify "objectively safe", for my part, I would want that to include cardiac function as well as physical damage. ESD apparently doesn't cause much damage; presumably it does, but it's microscopic and infrequent enough to ignore. And people don't usually fibrillate from it, AFAIK. Probably, somewhere in the HBM 10-20kV range is a reasonably-safe marker, in that region of pulse shape/amplitude/length.Tim

author: Manul
author_rank: Super Contributor
timestamp: February 26, 2021, 09:20:07 pm
content: Quote from: T3sl4co1l on February 26, 2021, 04:56:44 pmThis 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.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 26, 2021, 11:47:50 pm
content: 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.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.Tim

author: Manul
author_rank: Super Contributor
timestamp: February 27, 2021, 12:28:44 am
content: Quote from: T3sl4co1l on February 26, 2021, 11:47:50 pmI 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 pmThat's cool, but I dont understand where the antenna was mounted and what direction it was transmitting that people could sit in frontBut I'm sure it happened, because people are good to find solutions

author: Someone
author_rank: Super Contributor
timestamp: February 27, 2021, 12:50:57 am
content: Quote from: T3sl4co1l on February 26, 2021, 04:56:44 pmIEC 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 pmUnlike 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)

author: amyk
author_rank: Super Contributor
timestamp: February 27, 2021, 01:06:33 am
content: Related previous discussion:https://www.eevblog.com/forum/chat/whats-the-current-of-a-static-shock/