*Relevant summary: * In worst case conditions 10's of *micro*amps applied to the heart can cause ventricular fibrillation and death, Unusual but not wholly unlikely situations may occur in 'real life' where *much* lower than usually expected voltages and currents can cause death. ________________________ The post at the end just reappeared in response to a search re "testing an ac motor" posts. I copy it below untrimmed. Original subject line was "[OT] Danger of DC Power Supply" This is worth added comment as I have recently encountered an article that provided new (to me) information on the minimum amount of current which may kill in worst case cases. I have never been very happy with some of the commonly offered advice re "safe" currents and have been aware of the fact that some people die in situations where currents seem to have been much lower than might be expected. *Death MAY occur with heart currents in the 10's of micro-amp range.* *That's MICRO-amps.* The "trick" is that this is HEART current - currents this low usually only apply to situations where: *From PDF below:* there is a high conductivity path into the heart itself - maybe a metallic conductor for instrumentation or a saline filled tube. *From powerpoint presentation below:* Patient with *breaks in skin like abrasions, wet dressings*, pacemakers, or monitoring lines connected to a transducer Note that the references below provide "statements of fact" without supporting data, and several have at least one author in common. Hoever, given the sources and contexts, Occam suggests that taking note pof what they say would be highly advisable. __________________ *See: "Electrical Safety in the Operating Room ..."* Populist & pretty http://danieljohndoyle.com/uploads/3/0/7/7/3077522/ccf_rc_electricalsafetyi= ntheoperatingroom_rev_2011.pdf Paper http://journals.lww.com/anesthesia-analgesia/Fulltext/2010/06000/Electrical= _Safety_in_the_Operating_Room__Dry.1.aspx *Powerpoint * http://www.uiowa.edu/~medtest/or_reference/ELECTRICAL%20Safety%20.pdf *Relatedish* https://www.google.co.nz/search?q=3D%22electrical+safety+in+the+operating+r= oom%22&biw=3D853&bih=3D571&tbm=3Disch&tbo=3Du&source=3Duniv&sa=3DX&ei=3DEp4= UVYOHLOOmmAXFqYGwBQ&ved=3D0CDIQsAQ *Video - 37 minutes* https://www.youtube.com/watch?v=3DQ-51Igy_J9A _________________________________ *PRIOR: two edits in [square brackets] added* On 21 November 2013 at 23:39, RussellMc wrote: > What kills is current through heart muscle locking > [affecting] > muscle and preventing > [normal] > heart action. Removal may or may not still kill - if heart fibrillates > (noisy electrical chaotic shimmer mode) rather than restarts you 'have > problems'. > > A <=3D 30VDC power supply will generally be safe. It's best to avoid > contact if possible, NOT work in damp conditions and not have a situation > where it can ever be applied across your chest. eg carrying a 24V lead ac= id > battery of any size with contacts against your chest or against a shirt i= f > you are sweaty COULD be fatal but is unlikely to be. > > 1. Rub your chest with saline solution and apply two 30V electrodes to > skin across heart or nearby and it has a good chance of killing you. > 12VDC applied via electrodes across a (convict) volunteers chest has > resulted in death. This was unexpected and in spite of resuscitation > attempts. > > 2. Stand in salt water with bare feet with one 30V terminal in water also > and brush other terminal with dry hand and you will PROBABLY not feel it. > > 3. Not many people know the following. I have a friend who experienced > this with 12V while flounder fishing with a pole lamp with a metal pole. = An > unexpected lockup experience. > As in 2. above but add saline to hand that grasps and grasp terminal so > there is hand - foot conduction and you may get muscle lockup in hand so > you cannot let go. This MAY kill you but that is very unlikely (providing > somebody unlocks your hand so you can wander off. > > 4. Generally under almost any circumstance you would normally meet you'd > not feel 30V or have adverse reactions BUT as above there can be exceptio= ns. > I'd regard 12V and below as essentially super safe, 24V as safe with a > soupcon of care and 30V as hardly worse. > > Work on a Telco wiring frame with 50V and no care is usually taken to not > make contact and no feelings of electricity present when you brush > contacts. BUT on a high humidity day you start to get annoying tingles > across the nuckles. > > 100 VDC will happily kill you in many cases BUT may not. I'd not grab two > 100V terminals for any reason that comes to mind. > > AC is generally safer than DC at any given voltage as your muscle > cyclically relax allowing release. > I have had perhaps dozens of 230 VAC shocks of various magnitude. > Plus a very few at 1000+ VDC > I try to avoid all such these days and have not had a decent shock for > some decades AFAIR. (A good shock across the head aka ECT may clear short > term memory, so one can never be sure :-) ). > > > > > Russell > > > On 21 November 2013 22:59, Lindy Mayfield wrote: > >> Up until now, my understanding of electricity and safety has been pretty >> basic. Batteries around the house, 9v etc, the development boards, I've >> been playing with, and so on, I don't worry it can hurt me. If it is >> household 220 v AC, then I treat it with respect. Even if I do know th= e >> light switch is off, I still test it with a multimeter to be double sure= .. >> >> But I don't know what comes out of this power supply. It goes up to 30 >> volts and 1 Ampere. So as an example, just touching wires on motors lik= e I >> would with a battery, can this thing be set high enough that I could get= a >> (bad) shock? >> > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .