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Electric shock pulse duration vs current vs lethality
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Manul:
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.
jpanhalt:
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?
Manul:

--- Quote from: jpanhalt on February 26, 2021, 03:02:24 pm ---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?

--- End quote ---

I'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.
jpanhalt:
If you are concerned about depolarizing nerves and/or myocytes of the heart without 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.html

Permanent damage, of course, doesn't necessarily mean death.  Failure to function after such damage will depend on its extent.
T3sl4co1l:
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
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