Safety of this circuit (involving hand-to-hand current):

Question

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!

Answer 1

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.

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.

Answer 2

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:

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.

Answer 3

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.

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!