[SI-LIST] Re: threshold
- From: "McCoy, Bart O." <McCoy.Bart@xxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 30 Jul 2003 08:38:09 -0500
I'm no expert on this, but what I know I'll share:
The voltage/current at which we can "feel it" or "getting hurt" by it
is frequency dependent-- due to the physiology of the body, muscles, etc.
How *wonderful* that 60 hz is in probably the deadliest in our danger-zone
frequency band of 5 Hz - 500 Hz. 60 Hz is so potentially deadly
because it can cause muscle spasms/contraction that prevent you from
letting go of live voltage sources. Also, unknown to many people,
lower voltages like the home 110 V or 220 V can be more deadly that
higer voltages (neglecting the tens of kV range) because the initial jolt
of lower voltage sources is not sufficient to knock you off of the source
like maybe 440 V is.
Typically, transient currents of >= 1 mA can be felt. Whether or not
it's lethal depends on many factors, most importantly: (1) the duration
of the pulse (5-15 kV & up to 1 A for around 1 microsecond for carpet static
discharge) and
(2) whether that current gets routed near the heart. Currents as low as 40
mA, if they
pass through the heart for sufficient duration, can be lethal. Carpet
static is
not lethal because of it's short duration and the capacity of the body to
absorb
the net quantity of charge injected (maybe 1A for 1 microsecond).
Voltage and current are 2 different things-- the lethal potential of a
pure voltage source depends upon physiological factors that determine body
resistance. Dry, dead skin can have 100 kOhms of resistance while wet
clammy palms can be as little as 100 ohms. That, obviously, will have a
lot to do with the current that passes into your salty, good-conductor
nerves/blood/blood vessles.
That is why good electricians forced to work on live circuits avoid sticking
BOTH hands in a live junction box at the same time-- it decreases the
chances
- Bart McCoy
-----Original Message-----
From: Clewell, Craig [mailto:cclewell@xxxxxxxxxxxxxx]
Sent: Wednesday, July 30, 2003 7:55 AM
To: 'si-list@xxxxxxxxxxxxx'
Subject: [SI-LIST] Re: threshold
...that would depend on weather you are James Bond or an ordinary citizen.
However, this may help ~~>
http://hypertextbook.com/facts/2000/JackHsu.shtml
http://www.smud.org/safety/world/hurt/chart.html
-----Original Message-----
From: hariharan [mailto:hariharan@xxxxxxxxxxx]
Sent: Wednesday, July 30, 2003 8:44 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] threshold
what is the threshold Voltage (V) and current (amps) beyond which human
beings can get hurt or feel it?
any idea...??
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