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

[Sam Sampere <smsamper@syr.edu>]

Think about the energy stored in the thing. Your VdG has a capacitance of pF. If your VdG is charged to 50,000 V, the energy is something like mJ. My 7kV 100 uF capacitor is almost 2kJ. Imagine a 1 kg mass dropped from a couple football fields high hits your head... 

So, it's not really, current, it's not really voltage, it's really the energy delivered (or absorbed). 

Thanks,

Sam


-----Original Message-----
From: Phys-l <phys-l-bounces@mail.phys-l.org> On Behalf Of Bill Norwood via Phys-l
Sent: Tuesday, December 18, 2018 10:12 AM
To: Phys-L@phys-l.org
Cc: Bill Norwood <bnorwood111@gmail.com>
Subject: Re: [Phys-L] Current or Voltage is the thing that kills?

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=20miliAm
> > ps
> 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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> > Phys-l@mail.phys-l.org
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