-=> ROBERT SAYRE wrote to WAYNE CHIRNSIDE <=-

 WC> I can make a case for a the hazards of a few picoamperes
 WC> as there's a case where a pacemaker patient was placed on a grounded
 WC> hospital bed and the leakage current from that device offed him.

 RS>  You've got me baffled here.

 RS>  The pacemaker wouldn't know nor care if the
 RS> patient were grounded or not. Or, are you
 RS> talking about a pacer on a defibrillator?
 RS> Even then, ground should not matter.

 I thought not either but I vividly recall the incident and
 those there proclaimed that the cause of death.
 Perhaps the doctor f'ed up and blamed it on the pacemaker?
 At any rate those pacemakers were recalled.
 Still I can hold a lousy NE-2 in my hands without a 
 current limiting resistor and light it off the hot on an outlet
 with only a wood floor, concrete, soil and the ground at the pole as
 return.
 
 RS>  (Hospital beds are always grounded.)

 RS>  As far as picoamperes, we allow a maximum
 RS> of 300 microamperes of leakage on devices
 RS> used in surgery. This is considered safe.
 RS> The law allows 500 microamperes. Even the
 RS> heart/lung machine I work on allows up to
 RS> 20 microamperes of leakage.

 Yeah but here we're talking about the lead that's in intimate
 contact with the heart muscle, another matter entirely.
 
 RS>  I must be missing something.

 Don't know just know what I read.

 MR> In the shock effects literature it can be found that
 MR> heart rhythm problems occur within a narrow current range of a few
 MR> milliamperes. Less than this range there is no effect, higher and fles
 MR> burns result but the heart survives.

 Yeah I got a 2 gauge braided aluminum wire tattooed on my
 arm when my idiot partner hooked up the safety ground against me
 explicit instructions not to do so when hooking up a 200 amp service
 to a mobile home to the lines right off the transformer.
 I could feel every muscle in my body trying to jump at 60 CPS
 but being unable to keep up with the voltage reversals referenced to
 ground. The idiot said he was just trying to get done quicker :-(
 Well I was almost _done_ quicker.

 WC> Genrally the lethal level is around 17 -20 MA. but than there's
 WC> that matter of skin resistence again.

 RS>  Typically, 10 ma is considered lethal.

 My sources say a bit more but we're well in the same ballpark.
 Interestingly women are slightly more at risk at the lower end of that
 range.

 RS>  Skin resistance is taken into consideration
 RS> by stating the current, as primarily that
 RS> resistance will determine the amount of
 RS> current that will flow.

Along with taking into consideration the voltage pushing it.
I'll take 10,000 amperes with one hand on each line but only if the
voltage is under six volts ;-)

 WC> Now if you pierce the skin with a charged line that's another matter
 WC> entirely however even then AC is more dangerous than DC but you will
 WC> feel a jolt.

 RS>  Regardless how the current gets there, it is
 RS> the amount of current that is important. Lower
 RS> resistance ("if you pierce the skin") will
 RS> allow more current to flow, even with lower
 RS> voltages. The inside of the body is relatively
 RS> low resistance (<50 ê).

Quite correct

 RS>  Once you reach about 10 ma, that current will
 RS> "overpower" the current running your heart and
 RS> will "control" the heart. Different people are
 RS> different, but 10 ma is typical. AC or DC, it
 RS> will not allow the heart to beat.

 My understanding is that DC will cause the heart to clamp while 
 AC is more inclined to induce fibrillation.
 
 RS>  Perhaps a lower AC voltage would "interfere"
 RS> with the heart before the same level of DC
 RS> would, but I've never heard of it. I'll ask
 RS> the other guys at work tomorrow, to be sure.

Got my stuff off internet search engine which backs up 
anecdotal info I had prior to net access.
 

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