The following was excerpted from within this page (a good tutorial on ELECTRICAL SAFETY btw): http://www.ibiblio.org/obp/electricCircuits/DC/DC_3.html - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - But how much current is harmful? The answer to that question also depends on several factors. Individual body chemistry has a significant impact on how electric current affects an individual. Some people are highly sensitive to current, experiencing involuntary muscle contraction with shocks from static electricity. Others can draw large sparks from discharging static electricity and hardly feel it, much less experience a muscle spasm. Despite these differences, approximate guidelines have been developed through tests which indicate very little current being necessary to manifest harmful effects (again, see end of chapter for information on the source of this data). (Electric shock data, obtained from online (Internet) sources: the safety page of Massachusetts Institute of Technology (website: [*]), and a safety handbook published by Cooper Bussmann, Inc.) BODILY EFFECT DIRECT CURRENT (DC) 60 Hz AC 10 kHz AC --------------------------------------------------------------- Slight sensation Men = 1.0 mA 0.4 mA 7 mA felt at hand(s) Women = 0.6 mA 0.3 mA 5 mA --------------------------------------------------------------- Threshold of Men = 5.2 mA 1.1 mA 12 mA perception Women = 3.5 mA 0.7 mA 8 mA --------------------------------------------------------------- Painful, but Men = 62 mA 9 mA 55 mA voluntary muscle Women = 41 mA 6 mA 37 mA control maintained --------------------------------------------------------------- Painful, unable Men = 76 mA 16 mA 75 mA to let go of wires Women = 51 mA 10.5 mA 50 mA --------------------------------------------------------------- Severe pain, Men = 90 mA 23 mA 94 mA difficulty Women = 60 mA 15 mA 63 mA breathing --------------------------------------------------------------- Possible heart Men = 500 mA 100 mA fibrillation Women = 500 mA 100 mA after 3 seconds --------------------------------------------------------------- Research has provided an approximate set of figures for electrical resistance of human contact points under different conditions (see end of chapter for information on the source of this data): Wire touched by finger: 40,000 O to 1,000,000 O dry, 4,000 O to 15,000 O wet. Wire held by hand: 15,000 O to 50,000 O dry, 3,000 O to 5,000 O wet. Metal pliers held by hand: 5,000 O to 10,000 O dry, 1,000 O to 3,000 O wet. Contact with palm of hand: 3,000 O to 8,000 O dry, 1,000 O to 2,000 O wet. 1.5 inch metal pipe grasped by one hand: 1,000 O to 3,000 O dry, 500 O to 1,500 O wet. 1.5 inch metal pipe grasped by two hands: 500 O to 1,500 kO dry, 250 O to 750 O wet. Hand immersed in conductive liquid: 200 O to 500 O. Foot immersed in conductive liquid: 100 O to 300 O. - - - - - - - - - - - - - - - - - - - - - - Electric shock data The table of electric currents and their various bodily effects was obtained from online (Internet) sources: the safety page of Massachusetts Institute of Technology (website: [*]), and a safety handbook published by Cooper Bussmann, Inc (website: [*]). In the Bussmann handbook, the table is appropriately entitled Deleterious Effects of Electric Shock, and credited to a Mr. Charles F. Dalziel. Further research revealed Dalziel to be both a scientific pioneer and an authority on the effects of electricity on the human body. The table found in the Bussmann handbook differs slightly from the one available from MIT: for the DC threshold of perception (men), the MIT table gives 5.2 mA while the Bussmann table gives a slightly greater figure of 6.2 mA. Also, for the "unable to let go" 60 Hz AC threshold (men), the MIT table gives 20 mA while the Bussmann table gives a lesser figure of 16 mA. As I have yet to obtain a primary copy of Dalziel's research, the figures cited here are conservative: I have listed the lowest values in my table where any data sources differ. These differences, of course, are academic. The point here is that relatively small magnitudes of electric current through the body can be harmful if not lethal. Data regarding the electrical resistance of body contact points was taken from a safety page (document 16.1) from the Lawrence Livermore National Laboratory (website [*]), citing Ralph H. Lee as the data source. Lee's work was listed here in a document entitled "Human Electrical Sheet," composed while he was an IEEE Fellow at E.I. duPont de Nemours & Co., and also in an article entitled "Electrical Safety in Industrial Plants" found in the June 1971 issue of IEEE Spectrum magazine. For the morbidly curious, Charles Dalziel's experimentation conducted at the University of California (Berkeley) began with a state grant to investigate the bodily effects of sub-lethal electric current. His testing method was as follows: healthy male and female volunteer subjects were asked to hold a copper wire in one hand and place their other hand on a round, brass plate. A voltage was then applied between the wire and the plate, causing electrons to flow through the subject's arms and chest. The current was stopped, then resumed at a higher level. The goal here was to see how much current the subject could tolerate and still keep their hand pressed against the brass plate. When this threshold was reached, laboratory assistants forcefully held the subject's hand in contact with the plate and the current was again increased. The subject was asked to release the wire they were holding, to see at what current level involuntary muscle contraction (tetanus) prevented them from doing so. For each subject the experiment was conducted using DC and also AC at various frequencies. Over two dozen human volunteers were tested, and later studies on heart fibrillation were conducted using animal subjects. + - + - + - + - + - + - + - + - + - RF Jim ----- Original Message ----- From: "Dwayne Reid" To: Sent: Saturday, November 02, 2002 2:54 PM Subject: Re: [PIC]: Direct LED connection? > At 12:34 PM 11/2/02 +1100, Sean Alcorn - Avion Sydney wrote: > > >>I believe GFIs in the US are supposed to trip at 7 or more ma. > > > >I have often wondered about this. I have done some paramedics training, > >and from memory - doesn't the heart start to fibrillate at about 25mA. > >I've often thought it cruel that - if my memory is correct and it is > >indeed 25mA - our RCCBs are set at 30mA :-) > > Articles that I have read in the distant past suggested that 50 Hz is MUCH > less likely to induce ventricular fibrillation than 60 Hz - IIRC, the most > susceptible frequency is somewhat above 60 Hz. I don't recall the specific > details but I'll try to look it up later this weekend. > > dwayne > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu