Re: Tesla Coil safety question

To: tesla-at-pupman-dot-com
Subject: Re: Tesla Coil safety question
From: Bert Hickman <bert.hickman-at-aquila-dot-com> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Sat, 05 Sep 1998 17:50:35 -0600
Approved: terryf-at-verinet-dot-com
Tesla List wrote:
> 
> Original Poster: bob985-at-earthling-dot-net
> 
> I am planning on showing my 9kV, 30ma coil to some
> friends, and I am wondering how safe it would be to be
> holding onto a bolt and then let the 7" sparks from the
> torroid conduct through the bolt to me.
> 
> I recal hearing that this is fairly safe because the
> electricity is at such a high frequency, it only
> travels over the surface of the skin, making it
> non-lethal.
> 
> Is this correct? Has this been done by others? Who are
> still alive?
> 
> Thanks,
> 
> -Nathaniel
> Who is kinda new to this hobby.
> 
> -----------------------------------------------------
> Get free personalized email at http://yahoo.iname-dot-com

Nathaniel,

It is possible to take hits off a small disruptive (or vacuum tube)
coil. Most coilers holding onto a piece of metal so that the sparks
don't make little "burn holes" in your skin. You want to make sure that
you're not grounded - standing on an old plastic milk crate is a good
approach - and make sure that all elbows, knees, etc are far away from
any other objects or people. 
 
The so-called "skin effect" that works so well for metal conductors, is
not really applicable due to the relatively poor conductivity of your
body, which internally is roughly that of sea water. Sea water is about
100 million times poorer a conductor than copper. As a result, the skin
effect for currents flowing through your body at Tesla Coil frequencies
is virtually non-existent(!)- the skin depth is of the order of 31+
inches at 100 kHz! Even at the much higher frequencies used in medical
diathermy (13 and 27 MHz), the penetration depth is still 2-3 inches! 

The reason why you feel little if any shock is NOT because the current
isn't flowing _through_ your body... it's because your nerves cannot
respond to the high frequency current. This does NOT mean that they, and
other internal tissues, cannot be damaged or even destroyed! It's
possible to sustain significant internal tissue damage and yet feel
nothing (at least immedialtely). This can be a significant problem when
taking hits off a higher-power tube-powered CW coil. You'll typically
feel absolutely NOTHING at the time, save a bit of thermal heating...
your fingers, hand and even your arm arm may get warm. Minutes or hours
later, you may feel aches and pains in your muscles and joints from
internal tissue damage! It's your body's way of telling you "Don't do
that anymore!!" <:^]

Now taking 7" hits from your low power disruptive coil should not be a
problem if you remember to be careful. The main risk here is a
primary:secondary flashover that could connect you to the very dangerous
primary circuit. That's why it's important that you NOT be grounded.
However, taking hits from a larger coil can be quite dangerous,
particularly for high power disruptive coils using large topload
capacitance. These can pack quite a wallop! We want all of our list
members to come back to learn and play another day! :^) 

Good luck, and safe coilin' to you!

-- Bert --