Ed Phillips wrote:
Ed --- can you give us a brief summary
especially of the let-go / no let-go points?
I was hit with a 15/30 back in 1962 and never
forgot it. Hurt like H but I only touched the
wire with the back of my hand. Had I enclosed
the wire with my fist things might have turned out differently.
Dr. Resonance"
Ed asked the question. "dwp" apparently read the paper.
Ed
A web accessible concise summary can be found on
pages 4-11 of "A Guide to Electrical Safety"
from the North Carolina Dept of Labor:
http://www.nclabor.com/osha/etta/indguide/ig18.pdf
An interesting graph (Figure 2 on page 4) shows
the electrocution threshold (in mA flowing
through the chest) for a typical adult versus
time flowing through the body. The thresholds
for a child may be significantly lower.
The following was extracted from the above paper:
"Based on the research of Professor Dalziel of
the University of California, Berkeley, the
effect of 60 Hz (cycles per second) of
alternating current on the human body is generally accepted to be as follows:
? 1 milliamp (mA) or less?no sensation?not felt
? 3 mA or more painful shock
? 5 mA or more?local muscle contractions?50 percent cannot let go
? 30 mA or more?breathing difficult?can cause unconsciousness
? 50100 mA?possible heart ventricular fibrillation
? 100200 mA?certain heart ventricular fibrillation
? 200 mA or more?severe burns and muscular
contractions?heart more apt to stop than fibrillate
? Over a few amps?irreversible body damage"
"Thus, we can see that there are different types
of injuries that electricity can cause. At the
20 to 30 mA range a form of anoxia (suffocation)
can result. This could happen in a swimming pool
where there is a ground loop present (the drain
at the bottom of the pool) if a faulty light
fixture or appliance is dropped into the water.
Current would flow from the light fixture to the
drain, using the water as the conducting medium.
Any person swimming through the electrical field
created by the fault current, would be bathed in
potential difference and the internal current
flow in the body could paralyze the breathing
mechanism. This is why it is very important to
keep all portable electrical appliances away from sinks, tubs and pools."
"Ventricular fibrillation generally can occur in
the range of 50 to 200 mA. Ventricular
fibrillation is the repeated, rapid,
uncoordinated contractions of the ventricles of
the heart resulting in the loss of
synchronization between the heartbeat and the
pulse beat. Once ventricular fibrillation
occurs, death can ensue in a few minutes.
Properly applied CPR (cardiopulmonary
resuscitation) techniques can save the victim
until emergency rescue personnel with a
defibrillator arrive at the scene. Workers in
the construction trades and others working with
electrical power tools should receive CPR training."
Above a few amperes, irreversible body damage
can occur. This condition is more likely to
occur at voltages above 600 volts AC. For
example, if a person contacted 10,000 volts, I =
10,000/1,000 = 10 amps. This amount of current
would create a great amount of body heat. Since
the body consists of over 60 percent water, the water would turn to steam at a
ratio of approximately 1 to 1,500. This would
cause severe burns or exploding of body parts.
These are the types of injuries that you would
normally associate with electric power company
workers. They can also occur, however, when
people accidentally let a television or radio
antenna contact an uninsulated power line.
Accidents involving mobile vertical scaffolding
or cranes booming up into power lines can cause
these types of injuries or fatalities."
The above paper implies that, although 30 mA NST
may not provide a fatal shock to a healthy
adult, it could cause suffocation and loss of
consciousness. A sustained shock from a 60 mA
NST might be fatal (from ventricular
fibrillation) if the victim couldn't free
himself from being part of the current path.
Either shock would be quite painful... =<:^o
Bert
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