Re: TC discharge... safe or not

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

All,

OK... some numbers coming up.

The resistivity of human flesh varies depending upon the type of tissue, 
ranging from about 150 ohm-cm (blood) to about 2500 ohm-cm (fat). The 
surface resistivity of dry skin can be considerably higher.  An average of 
about 400 ohm-cm is typically used for estimating bulk resistivity for 
humans. For comparison seawater, being "saltier" and a better ionic 
conductor, has a resistivity of about 25 ohm-cm. For comparison, annealed 
copper runs about 1.7 microohm-cm, making copper over 200 million times 
more conductive than an average human being. Humans make fairly good water 
resistors but lousy conductors unless we get overloaded and begin carbon 
tracking...  =:^(

The "skin depth" of a conductor is defined as the point at which the 
current flow declines to 1/e, or about 37% of the total current. Skin depth 
is a function of a material's electrical conductivity (the reciprocal of 
its resistivity), it's magnetic permeability, and applied frequency. It can 
be estimated using the following equation:

    Skin Depth = 1/(SQRT(Pi*F*Mu*Conductivity))

Plugging in the numbers for some common materials at 100 kHz and converting 
to english measurements:

  Pure iron         =  0.26 mils
  Cold Rolled Steel =  1.48 mils
  Copper            =  8.23 mils
  Tungsten          = 14.71 mils
  Carbon            = 62.66 mils
  Sea water         = 31.33 INCHES
  Human Flesh (ave) = 10.44 FEET(!)

The above table sheds some light on why you wouldn't want to wind a 
resonator or primary using a steel conductor. More importantly, it also 
shows that (at Tesla Coil frequencies) skin effect is virtually 
_nonexistent_ for human beings unless you happen to be large enough to 
merit your own zip code! RF current from a Tesla Coil will pass THROUGH 
your most conductive tissues and organs: blood, nerves, and muscles and 
will certainly NOT stay on your skin. In fact, RF current pokes holes 
through your more resistive skin and fat layers (often cauterizing and 
carbonizing them in the process) to get to your juicier, more conductive, 
interior. RF burns can be quite painful and they take a very long time to heal.

So, what are the medical risks of passing RF currents from Tesla Coils 
through your body?? We don't really know! There's anecdotal evidence that 
at least temporary tissue damage has occurred in folks who have passed 
larger currents (especially from CW systems). In high school I experienced 
joint pains several hours after drawing multi-ampere currents from a VTTC 
(lighting multiple 100W light bulbs). I've never had any symptoms from 
small disruptive coils. I know of at least three other coilers who have 
reported similar joint pain from CW coils.

While short duration or low power levels are _probably_ safe (or at least 
safer), we really don't know for sure. Play safely - you'll need to make 
your own decisions on safety and risks.

Best regards,

-- Bert --
-- 
Bert Hickman
Teslamania, from Stoneridge Engineering
"Electromagically" (TM) Shrunken Coins
http://www.teslamania-dot-com

Tesla list wrote:
>Original poster: "Jeff W. Parisse by way of Terry Fritz 
><twftesla-at-qwest-dot-net>" <jparisse-at-teslacoil-dot-com>
>Ken (et. al.)
>  > Not to try to attack anybody, but Jeff mostly states "I'm not an
>engineer"
>  > and then hearsay with no numbers involved. The whole field seems and
>probably
>  > is quite empirical, for which there are no hard facts when it comes to
>what
>  > is or is not safe, just your judgement based off hearsay and sometimes
>common
>  > sense.
>To set the record straight, I say:
>"I'm not an engineer but I play one on TV."  ;-)
>We don't give out numbers like Kentucky Fired Chicken doesn't give out
>recipes. I run a business, it's nothing personal. We also don't
>encourage
>Americans to try crazy stunts because when they fail they like to sue
>(i.e.
>fat people suing McDonalds, smokers suing their long time brands, etc.).
>There's a ton of number crunching, CAD and modeling going on at kVA
>Effects.
>But like most technology companies, it is for in-house use only.
>Jeff
>
>Jeff W.Parisse
>www.teslacoil-dot-com
>