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Working at the national lab in Los Alamos there were some signs which said,
"Danger High Current." This was on a 5 volt bus that supplied power to a
few thousand detectors. Sure, you could touch the terminals with your
hand, but drop a wrench across those terminals and it would blow up in your
face.
This leads to another point on the hazards of electricity... there are
multiple ways that it can kill you.
1) There is the obvious cooking way where lots of power is dissipated in
your flesh, raises body temperature and chars important organs. This seems
to be the way that most of you are thinking about.
2) Arc Flash - a very brief flash from a breaking contact could simply set
you on fire. Then again it may produce a hot plasma cloud in your
vicinity. The human reflex to such a shock is to inhale. Needless to say,
hot plasma is bad for the lungs. (Always inhale before you flip a circuit
breaker.)
3) Wires or stuff simply exploding.
4) Enough current to cause your muscles to tense and freeze in place. This
might not burn you, but if one of the muscles is your diaphragm, your won't
be able to breathe.
5) Stopping your heart. I'm no expert on the physiology of cardiac shock,
but I am certain that a typical AED does not provide sustained high
current. Whatever the voltage and pulse duration, it has a serious impact
on the cardiac rhythm. What other sources might cause this, I wouldn't
venture to guess.
That's probably not an exhaustive list, but it's enough to give you a
healthy respect for electrical power.
Paul
On Tue, Dec 18, 2018 at 9:12 AM Bill Norwood via Phys-l <
phys-l@mail.phys-l.org> wrote:
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?electrical
On Tue, Dec 18, 2018 at 8:27 AM Peter Schoch wrote:
Hello,
I have always used the phrase "current kills" when discussing
I={\fracsafety for my lab safety lectures. One of my references is:wrote
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
me the following:
"...here are my calculations and conclusions: ohms law: [image:
resistance.{V}{R}},] states that current is equal to voltage divided by
.01This means that current is limited by by the voltage of the circuit andthe
inverse of the resistance of the circuit. That being said, humans arenot
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 -
isn'tohm range, meaning that there is a minimum of 3 orders of magnitudeeven a
difference between the resistance of wet skin (e.g. your tongue) and
bad wire. Thus, if you have a power supply producing 10 volts, even ifthe
current it can produce is infinite, the maximum that could run throughyour
tongue is given by: [image: LaTeX:This
I=\frac{10}{500}=.02\:amps\:=\:20\:miliAmps]I=10500=.02amps=20miliAmps
is enough to hurt and even cause strong muscle contractions, but it
exactlyenough 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
dampwhat Mehdi Sadaghar does to himself. However, for dry or even mildly
"currentskin, 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
people,kills, not voltage" is similar to saying that cancer doesn't kill
completelyorgan failure does. While this isn't strictly wrong, it isn't
alsotrue either, and it can give people the wrong impression. This would
voltageexplain why warning signs say 'High voltage' not 'High Current'."
While I agree that you can't have a current without a sufficient
toweek
move it, they don't 'discover' that in lab until the second or third
with(the first week or two being spent on just familiarizing themselves
inthe various peices of equipment and what they do).kills"
Ultimately, my question is -- Should I stay with my simple "current
message to drive home the necessity for safety; or, should I ammend it
_______________________________________________some way?_______________________________________________
Thanks,
Peter Schoch
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