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>  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.

WC>  Yeah but here we're talking about the lead that's in intimate
WC>  contact with the heart muscle, another matter entirely.

 It takes >50uA to stimulate the heart.
Pacemakers typically put out 10 times this
amount as a "safety margine" to insure a
response.

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.

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

 With friends like these, ...

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.

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

 The "rule of thumb" is 100 ma through the body, but
through the heart is about 10 ma. Of course you can
still die by going into fibrillation with a lower
current through the heart, and the wave form makes a
difference, too.

 There is a rather wide range due to the physical
sizes of people. Some have a lot more parallel paths
through their body (tall and husky) than do others
(short and thin) and different amounts of fats, etc.

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.

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

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.

WC>  My understanding is that DC will cause the heart to clamp while
WC>  AC is more inclined to induce fibrillation.

 Depends on the instant it was applied and for how
long.

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.

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

 What I was told today is that AC is more likely
to cause a "hit" at the WRONG time as it hits 120
times per second. With DC, the odds of not
"hitting" at the wrong time are much better. ;^)

 TTYL.

 Robert

 * SLMR 2.1a * "This man's dying!""Dammit, Jim, I'm a
doctor, not...oh."

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