Re: [Phys-L] Current or Voltage is the thing that kills?

[Bill Norwood <bnorwood111@gmail.com>]

As in most other potentially hazardous exposures time is a factor.

If I remember correctly one can conduct 10 amperes for 1 microsecond from a
van de graff generator and be unharmed. Done it myself hundreds of times.

Bill Norwood
U of Md at College Park

On Tue, Dec 18, 2018, 8:47 AM Paul Fedoroff via Phys-l <
phys-l@mail.phys-l.org> wrote:

> How about just saying Power?
>
> On Tue, Dec 18, 2018 at 8:27 AM Peter Schoch <pschoch@fandm.edu> wrote:
>
> > Hello,
> >
> > I have always used the phrase "current kills" when discussing electrical
> > safety for my lab safety lectures.  One of my references is:
> > https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html
> >
> > Now, one of my students has found:
> > http://www.electroboom.com/?p=450
> >
> > that contradicts it.  In response to this video, a thoughtful student
> wrote
> > me the following:
> > "...here are my calculations and conclusions: ohms law: [image: I={\frac
> > {V}{R}},] states that current is equal to voltage divided by resistance.
> > This means that current is limited by by the voltage of the circuit and
> the
> > inverse of the  resistance of the circuit. That being said, humans are
> not
> > good conductors, relative to metal such as in wires. In fact, a typical
> > resistance for 'human' is anywhere from 500(very wet skin)- 100,000(dry
> > skin) Ohms. For comparison, a typical wire is usually around the .1 - .01
> > ohm range, meaning that there is a minimum of 3 orders of magnitude
> > difference between the resistance of wet skin (e.g. your tongue) and
> even a
> > bad wire. Thus, if you have a power supply producing 10 volts, even if
> the
> > current it can produce is infinite, the maximum that could run through
> your
> > tongue is given by: [image: LaTeX:
> > I=\frac{10}{500}=.02\:amps\:=\:20\:miliAmps]I=10500=.02amps=20miliAmps
> This
> > is enough to hurt and even cause strong muscle contractions, but it isn't
> > enough to kill, which is 60 miliAmps (for DC it is actually higher than
> > this), and this is on your tongue. In fact, in the video, this is exactly
> > what Mehdi Sadaghar does to himself. However, for dry or even mildly damp
> > skin, this value would be < 1 miliAmp, which would not even be felt. So
> > while it is in fact the current that kills you, saying only that "current
> > kills, not voltage" is similar to saying that cancer doesn't kill people,
> > organ failure does. While this isn't strictly wrong, it isn't completely
> > true either, and it can give people the wrong impression. This would also
> > explain why warning signs say 'High voltage' not 'High Current'."
> >
> > While I agree that you can't have a current without a sufficient voltage
> to
> > move it, they don't 'discover' that in lab until the second or third week
> > (the first week or two being spent on just familiarizing themselves with
> > the various peices of equipment and what they do).
> >
> > Ultimately, my question  is -- Should I stay with my simple "current
> kills"
> > message to drive home the necessity for safety; or, should I ammend it in
> > some way?
> >
> > Thanks,
> > Peter Schoch
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