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circuit diagram

Note1: The voltage source in diagram is 3 lantern cells in series. Note2: Hands are placed on acrylic/plastic mesh so not directly in contact with metal trays.

The hands would be submerged for 20-30 minutes at a time and process would be repeated (say, every day). Given the hand-to-hand contact and submerged hands, I'd like to know what level of current would be expected to flow (in particular through the heart) and if there's any (non-negligible) risk associated with this circuit in both the short- and long-term.

I've looked at previous, more general threads about safe levels of current/voltage (How much voltage is "dangerous"?, Safe current limit for human contact?) and realise that there are too many variables to give exact answers to those but I'm hoping the specifics of this setup will allow for a more definitive answer!

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  • \$\begingroup\$ One way to avoid dangerous currents would be to use a current limiter (resistor, or maybe an LM317). And for my curiosity: why do you want to do this? \$\endgroup\$ – Wouter van Ooijen Apr 13 '14 at 18:54
  • \$\begingroup\$ If you won't provide any more information, then it would be a good idea to put a 10-megohm resistor in series with each wire to the metal trays. Using two resistors provides redundancy for added safety. Feel free to use higher resistor values if you like. \$\endgroup\$ – Joe Hass Apr 13 '14 at 20:00
  • \$\begingroup\$ @JoeHass In the spirit of "homeopathic dilution", less (current) may be more. \$\endgroup\$ – Spehro Pefhany Apr 13 '14 at 20:21
  • \$\begingroup\$ @WoutervanOoijen/Joehass Thank you for the replies, I guess I'll have to look into the min current needed for it to be effective (see below) and try work out appropriate resistance values from there. As for motive: it's a cheap version of an iontophoresis machine (used to treat hyperhidrosis). Other people have used the same setup (you can find videos/discussion etc online) and have been fine but with the water/hand-to-hand aspects of it it just seems potentially dangerous. The commercial machines are considered safe so it's obviously possible, it's just a shame they cost £400-500! \$\endgroup\$ – user40315 Apr 13 '14 at 20:49
  • \$\begingroup\$ I guess that such a treatment wants to achieve a specific (range of) current. Assuming that those currents are safe, current-limiting seems to be the best approach. Combine J.Hass's suggestion with mine and put two LM317's in series :) \$\endgroup\$ – Wouter van Ooijen Apr 13 '14 at 21:23
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So the idea is to deliberately plug sweat glands with minerals in tap water? And polarity doesn't matter at all?

I see at least one commercial unit has adjustable range 0.1-4mA which certainly has the potential to have some kind of effect on human tissue. It's well above the lethal current if injected directly into the heart, BTW, so I don't know if anyone can guarantee complete safety.

enter image description here

The other metric in that Powerpoint is the current density of 0.1-0.5 mA/cm2. I don't know how many cm2 my hand is, but if I guesstimate 500 (that estimate is in line with the 2.5% of body surface area (BSA) from this paper, and the Wikipedia estimate of 1.9m^2 for the average male BSA), that would be 50-250mA, which is well within the range that can cause venticular fibrillation. I suppose that your aim is to increase the exposure time and use a lower current density. If there is an area not requiring "treatment", then exposing it to the water is just putting unnecessary current through the body of the subject.

Your circuit depends on some unknown and variable resistances to limit the current. It may well be perfectly safe all or most of the time, but it's pretty hard to predict. Wouter/JoeH's idea of two series (redundant) current limits, keeping the overall limit to less than a few mA (and the voltage to less than 20V and definitely battery-powered with no mains connection at all) may be the best you can do, but I must repeat, I don't think anyone can guarantee safety of this circuit- some individuals may have more sensitivity, less internal resistance or something like a pacemaker that causes them to react differently.

It's possible that the high price of the commercial units is at least partially related to the cost of insurance against such claims.

As far as I understand it, this device exceeds the 1975 AHA recommended limit for long term DC patient leakage (eg. for external ECG patient electrodes) by a factor of 400:1. AFAIUI, the IEC-60601-1 limit is also 10uA for long term DC current. There may be some justification for an exception based on the really large contact area, but.. Apparently long-term DC current can cause necrosis or ulceration.

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  • \$\begingroup\$ So long as its not injected directly into the heart, the current density of the commercial unit, 4 mA, not going to be nearly enough to hurt the heart. \$\endgroup\$ – Scott Seidman Apr 14 '14 at 1:25
  • \$\begingroup\$ So long as there's no catheter in ther heart, this is MACROSHOCK, not MICROSHOCK. Keep the DC current down below about 8 mA, and that will be below let go current. If you have an implanted device, don't do it. Fibrillation for DC is at hundreds of mA. \$\endgroup\$ – Scott Seidman Apr 14 '14 at 1:32
  • \$\begingroup\$ Yes, it exceeds the IEC and the NFPA limits for ECG leads, but those are in place for reasons that don't apply here -- the risk of microshock in an ICU where patients may have cardiac catheters that will bring high density current directly to the heart. This current is "diluted" if you will, by the cross sectional area of the arms and chest, with resistive dropoffs happening all along the way. \$\endgroup\$ – Scott Seidman Apr 14 '14 at 10:39
  • \$\begingroup\$ Noone seems to know exactly why it works - I think that's one hypothesis, another being that it affects nerve impulses. You have to reverse the polarity halfway through. I think that machine is for drug delivery (using same technique); examples of ones for hyper. are Idrostar/Idromed/Hidrex etc. They use up to 20mA (~30 for pulsed a.c. ones). That's what I don't really understand, it seems that theoretically there should be risks as you say yet the machines are endorsed by all the hyperhidrosis organisations, have been available for years and (most importantly?) are used in NHS hospitals. \$\endgroup\$ – user40315 Apr 14 '14 at 10:51
  • \$\begingroup\$ The currents in the ppt you cite are designed to deliver a therapeutic drug dose by iontophoresis. The electrodes for that are usually on one limb, and don't cross the heart (I've had it done), and the currents are higher than what should be used here. \$\endgroup\$ – Scott Seidman Apr 14 '14 at 10:59
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I would suggest consulting IEC 60479-1:2005, Effects of current on human beings and livestock, Part 1: General Aspects.

This is the standard that informs other electrical standards where safe touch and step voltages are concerned, i.e. for design of substation earthing systems.

Here is a snippet from the table of contents:

enter image description here

Note, hand-to-hand current is distinguished between other currents (i.e. hand to foot, chest to hand, foot to foot) by a Heart-current Factor F - see Table 12.

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  • \$\begingroup\$ Why would you copy the table of contents but not the relevant material? \$\endgroup\$ – Joe Hass Apr 14 '14 at 10:56
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    \$\begingroup\$ @JoeHass, not sure about that one but some IEC standards are paid-for / copyright, in which case this just might be a reasonable pointer to one worth purchasing. \$\endgroup\$ – PeterJ Apr 14 '14 at 11:01
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    \$\begingroup\$ @JoeHass I think that the TOC is freely accessible, but the content isn't. Even if Li had read it, probably it wouldn't be legal to share it. Not sure though. \$\endgroup\$ – clabacchio Apr 14 '14 at 11:02
  • \$\begingroup\$ Thank you for the recommendation, it looks expensive after a quick search but it looks like a useful resource in general so I'll do some digging later to see if I can find a cheaper copy. \$\endgroup\$ – user40315 Apr 14 '14 at 11:16
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    \$\begingroup\$ @JoeHass: As clabacchio has inferred, the table of contents can be freely accessed (i.e. from saiglobal.com) but you have to pay for the full document. I am OK with posting a few paragraphs or the occasional table, but in this case I would have had to post multiple pages of text to address OP's question, which I am not comfortable doing. \$\endgroup\$ – Li-aung Yip Apr 14 '14 at 11:52
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We're hearing a lot about IEC and NFPA99 codes and such, but those don't necessarily apply. It is CURRENT DENSITY, not CURRENT, that causes problems -- that is, current travelling through a small cross section near the heart can cause fibrillation. In the hospital setting, codes recognize that the sickest patients can have catheters with conductive fluid right in the heart, so requirements are strict. If you look at the graphs, by the way, DC current is much safer than 60Hz AC current from the fibrillation point of view.

enter image description here

If the suggested system can be held down to about 4 mA, which is less than let-go current (i.e., the current at which your muscles will contract, making it impossible to "let go" of the source of the shock), this should be relatively safe, as the current will cross the entirety of the chest. AVOID THIS IF YOU HAVE A PACEMAKER, OR ANY IMPLANTED ELECTRICAL DEVICE!!

The safer way to do this is to put both hands in the same bath, and use a large surface grounding electrode (like those used on TENS units -- http://www.tenspros.com/Electrodes_c_11.html?gclid=CPKXp_T4370CFUVp7AodEi4A1g ) on both forearms tied to the other battery lead (still with a current limiting circuit of some kind). Consider LIGHTLY abrading the skin under the ground pad with a plastic scrunchy, but this would make a current limiting circuit even more important (A resistor to limit to 4 mA). Perhaps one hand at a time might be better.

As has been pointed out, watch out for burns, or lesions that might be caused by long periods of DC current. I think the issue may be more important with implanted electrodes, with smaller surface areas and more electrochemistry going on. Use the largest ground pads you can find. If it hurts, STOP!

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