Human Body Capacitance and Resistance
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From: krw on 31 May 2010 00:38 On Sun, 30 May 2010 18:42:34 -0700, "Paul Hovnanian P.E." <Paul(a)Hovnanian.com> wrote: >Archimedes' Lever wrote: >> >[snip] >> >> As for an electrostatic event causing a fibrillation, it is not very >> likely until one gets up into the lightning bolt voltages. The time of >> stroke becomes a factor. > >Correct. 400pF doesn't store much energy at a few kV. At 3kV its 1.8 mJ. >Getting stuck to a 3kV DC source is a different matter. > >According to http://en.wikipedia.org/wiki/Defibrillation, it takes >hundreds of Joules to defibrillate a heart. 300J from chest to back, the best path possible. BTDT, burned a bit.
From: Winfield Hill on 31 May 2010 07:14 Robert Baer wrote... > > Winfield Hill wrote: >> >> The subject is ESD Human Body model values. I'm enamored by >> a 1989 symposium paper by Richard Fisher, of Sandia Nat'l Labs, >> where he created a "Severe Human ESD Body Model." His model >> had worst-case numbers meant for use in electrostatic-discharge >> circuit-protection analysis, etc. >> >> Fisher's Severe Body Model consists of two parts, the body and an >> arm with hand reaching out to zap something. The body part has >> 400pF of capacitance in series with 250 ohms and 0.5uH. Then the >> arm and hand part bridges the body terminals with 10pF, and finally >> we have another 110 ohms and 0.1uH in series to complete the model >> and connect it to the poor real-world victim. The body capacitance >> is higher than you may see elsewhere first because the body is >> sitting down, and second because it's a worst-case body. We won't >> go further into what that means. :-) >> >> You charge the 400pF capacitor to a voltage of your choosing. >> 20kV is a nice high number. During discharge we get a fast spike >> of current from the 10pF, with sub-ns risetime to dangerous levels, >> with up to 5A peak current, and lasting up to 5ns into the "load." >> This is followed by a slower discharge of the 400pF capacitance, >> lasting up to 200ns. >> >> This would be followed by, ahem, a postmortem. Let me point out that I was thinking of a component postmortem. >> As for the effect of high moisture and humidity, as said, these can >> affect things, e.g., lowering resistances to the low levels we see >> in Fisher's Severe Model, but it also means the maximum electrostatic >> voltage developed on the 400pF capacitor is likely to be much lower. >> I suspect Fisher would prefer to take the dry-air high voltage with >> the moist-skin low resistances for his Severe case. > I have known of two extreme cases of skin resistance: one person > could feel a slight "tingle" of he placed his hands between 120VAC > (himself in middle), and the other got killed when he accidentally got > himself in series with a SIX VOLT car battery ("good old days") - the > current thru the chest was more than sufficient to do the job. JEDEC standard JESD22-A114D spells out the familiar HBM ESD test model: 100pF in series with 1500 ohms. Fisher's Severe HBM was created from hundreds of measurements reported in the literature. His interest was in the worst-case observations. His 360-ohm value of body resistance is lower than you observe with simple ohm-meter measurements, etc., but keep in mind it's a high-voltage measurement. Is it reasonable to hope that our outer-skin-layer insulation can withstand a say 20kV discharge and maintain high-resistance? -- Thanks, - Win
From: Dirk Bruere at NeoPax on 31 May 2010 19:18 On 30/05/2010 12:49, Winfield Hill wrote: > A repost of a comment I made elsewhere, for discussion here. > > The subject is ESD Human Body model values. I'm enamored by > a 1989 symposium paper by Richard Fisher, of Sandia Nat'l Labs, > where he created a "Severe Human ESD Body Model." His model > had worst-case numbers meant for use in electrostatic-discharge > circuit-protection analysis, etc. > > Fisher's Severe Body Model consists of two parts, the body and an > arm with hand reaching out to zap something. The body part has > 400pF of capacitance in series with 250 ohms and 0.5uH. Then the > arm and hand part bridges the body terminals with 10pF, and finally > we have another 110 ohms and 0.1uH in series to complete the model > and connect it to the poor real-world victim. The body capacitance > is higher than you may see elsewhere first because the body is > sitting down, and second because it's a worst-case body. We won't > go further into what that means. :-) > > You charge the 400pF capacitor to a voltage of your choosing. > 20kV is a nice high number. During discharge we get a fast spike > of current from the 10pF, with sub-ns risetime to dangerous levels, > with up to 5A peak current, and lasting up to 5ns into the "load." > This is followed by a slower discharge of the 400pF capacitance, > lasting up to 200ns. > > This would be followed by, ahem, a postmortem. Well, since people regularly charge themselves up to at least 30kV (a 1 cm spark) I would say not. -- Dirk http://www.transcendence.me.uk/ - Transcendence UK http://www.blogtalkradio.com/onetribe - Occult Talk Show
From: Winfield Hill on 31 May 2010 20:09 Dirk Bruere at NeoPax wrote... > >On 30/05/2010 12:49, Winfield Hill wrote: >> A repost of a comment I made elsewhere, for discussion here. >> >> The subject is ESD Human Body model values. I'm enamored by >> a 1989 symposium paper by Richard Fisher, of Sandia Nat'l Labs, >> where he created a "Severe Human ESD Body Model." His model >> had worst-case numbers meant for use in electrostatic-discharge >> circuit-protection analysis, etc. >> >> Fisher's Severe Body Model consists of two parts, the body and an >> arm with hand reaching out to zap something. The body part has >> 400pF of capacitance in series with 250 ohms and 0.5uH. Then the >> arm and hand part bridges the body terminals with 10pF, and finally >> we have another 110 ohms and 0.1uH in series to complete the model >> and connect it to the poor real-world victim. The body capacitance >> is higher than you may see elsewhere first because the body is >> sitting down, and second because it's a worst-case body. We won't >> go further into what that means. :-) >> >> You charge the 400pF capacitor to a voltage of your choosing. >> 20kV is a nice high number. During discharge we get a fast spike >> of current from the 10pF, with sub-ns risetime to dangerous levels, >> with up to 5A peak current, and lasting up to 5ns into the "load." >> This is followed by a slower discharge of the 400pF capacitance, >> lasting up to 200ns. >> >> This would be followed by, ahem, a postmortem. > Well, since people regularly charge themselves up to at least > 30kV (a 1 cm spark) I would say not. Right you are. As I clarified earlier, I was thinking of a component postmortem. -- Thanks, - Win
From: Mycelium on 31 May 2010 21:32
On Tue, 01 Jun 2010 00:18:18 +0100, Dirk Bruere at NeoPax <dirk.bruere(a)gmail.com> wrote: >On 30/05/2010 12:49, Winfield Hill wrote: >> A repost of a comment I made elsewhere, for discussion here. >> >> The subject is ESD Human Body model values. I'm enamored by >> a 1989 symposium paper by Richard Fisher, of Sandia Nat'l Labs, >> where he created a "Severe Human ESD Body Model." His model >> had worst-case numbers meant for use in electrostatic-discharge >> circuit-protection analysis, etc. >> >> Fisher's Severe Body Model consists of two parts, the body and an >> arm with hand reaching out to zap something. The body part has >> 400pF of capacitance in series with 250 ohms and 0.5uH. Then the >> arm and hand part bridges the body terminals with 10pF, and finally >> we have another 110 ohms and 0.1uH in series to complete the model >> and connect it to the poor real-world victim. The body capacitance >> is higher than you may see elsewhere first because the body is >> sitting down, and second because it's a worst-case body. We won't >> go further into what that means. :-) >> >> You charge the 400pF capacitor to a voltage of your choosing. >> 20kV is a nice high number. During discharge we get a fast spike >> of current from the 10pF, with sub-ns risetime to dangerous levels, >> with up to 5A peak current, and lasting up to 5ns into the "load." >> This is followed by a slower discharge of the 400pF capacitance, >> lasting up to 200ns. >> >> This would be followed by, ahem, a postmortem. > >Well, since people regularly charge themselves up to at least 30kV (a 1 >cm spark) I would say not. Except that he was referring to the chip. D'oh! |