On Sun, Jul 5, 2009 at 9:15 PM, Sean Breheny wrote: > Very good points, Ruben. > > I once got to use an ESD simulator to test some equipment for > susceptibility. It was based on the human body model (I think 100pF > with 1K in series) and could charge that capacitance up to 15kV. I can > tell you that 8kV was definitely painful. I didn't try shocking myself > with anything higher. The typical ESD events that we experience when > shuffling around the floor are more in the 3 to 5kV range. > > Also, there are varying "definitions" of what is a safe voltage to > touch. I would be suspicious of anything more than 24V for a DC > source. I know from experience that, when my hands are dry, I can > touch 50V DC and not feel a thing, but if I do the same thing when I > am sweaty, it REALLY hurts. I once had an intern who told me that she > had touched a 48V battery pack and the whole side of her face went > numb. It was a hot July in a non air-conditioned warehouse. Based on > the jolts I had gotten from the same voltage, I definitely believed > her and cautioned her not to touch the bare battery terminals again! > It's really tempting to disregard the danger because a) for most of > the year our skin is dry enough that we don't feel it and b) it is > unlikely to cause lasting harm. However, my understanding is that 10mA > is the maximum safe level (most standards are even more strict, saying > something like 2mA), and 100mA can definitely kill you if it takes the > proper path through your body (around the heart or through the brain). > > Ohm's law works very well for most metals. It is not a very good model > for the human body. Sweat and grip pressure greatly change the amount > of current which will flow for a given voltage. I also greatly suspect > that, as the voltage climbs, there is a nonlinear increase in the > amount of current due to electrochemical breakdown of the skin. Also, > all bets are off once the skin is punctured because the internal body > fluids are MUCH more conductive. > > Sean But it would still technically follow ohm's law since the resistance of your body would change? -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist