Hi Moshe, You wrote: > I've been asked about this by a friend, and as I recall several people > on this list have the knowledge and experience: > > There is this device which is used by the end user on himself. Among > other things the device generates a 12V DC voltage between the user's > hand and his skin in other parts of his body. > > 1. What is the range of human body resistance expected ? > 2. How much current is expected to flow ? > 3. Are there medical (or other) regulations for this kind of > situation? > 4. What are the possible risks involved ? > 5. Can you point me to standards documents (US,Europe..)
I'm not an expert but the following may help: 1. Skin resistance is most significant, as inner tissue (meat) is primarily saline, so is relatively low resistance. Epidermal cells are fairly dry and tough, and the outer layers are effectively dead, so not much electron activity goes on here. If the skin is wet, particularly if wet with a conductive fluid. e.g. saline or weak acid, then body resistance can at extremes fall to about 1k 'ish. 2. Current flow is ohms law... V/R. But a.c. is augmented by capacitive coupling over the the high resistance skin, to the return electrode, and additionally over shoe soles to ground. I believe d.c. causes subcutaneous polarisation which may reduce current after a few seconds, what THAT does to the complection I don't know. 3. I don't know medical stuff, but ask a lady with an 'Electrolysis' hair removing machine. 4. Death is a fairly typical risk associated with current flowing through a body, lesser risks include ventricular fibrillation (death), burning, (ending in death), falling off a ladder (death), unconsciousness (leading to...death). All in all to be avoided I feel. A.c. seems to be more dangerous than d.c. 5. I think IEC 479-1 : 1994 Guide to the effects of current on human beings and livestock. Part 1, frequencies between 15Hz and 100Hz, and d.c. Published as PD6519 : Part 1 : 1995 is the relevant document. Many years ago, at another company, we changed our fire alarm system from a 12V to a 24V system, with a 24V lead acid battery on trickle charge at each alarm annunciator. The old Electrician, Ted, used to top up the batteries once a month and generally check things out. Shortly after the 'new' system was installed he was found at the bottom of a ladder, complaining of chest pains. He explained that since the new system was installed he was suffering from shortness of breath, and on this occasion had suffered a 'kick' (his words) from the battery which toppled him from his short ladder. Subsequent hospital tests showed irregular heart beat (fibrillation) consistent with Electro Cardio something-or-other, or d.c across the heart muscle. Next day he was fine. The point is that his hands were wet with battery acid when he checked the battery connections for tightness. The ensuing current was enough to jerk the muscles in his arm sufficiently to chuck him off the ladder, and to affect his heart. I still maintain that safe electrical machine are the ones that are unplugged, and that there was nothing wrong with candles. good luck, Chris Dupres EMC Specialist. VG Microtech. cdup...@vacgen.fisons.co.uk tel +44 (0) 1825 761077 fax +44 (0) 1825 768343 'Opinions expressed are personal, not necessarily Corporate'
