Re: VDG's - dangerous

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

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
> 
> Original poster: "Daniel McCauley by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>

> Yes, be careful.  Most people are under the impression that since a van de
> graaf generator is electrostatic, that it isn't dangerous.
> However, if you have a powerful VDG, and you have someone standing on an
> insulator (for hair raising) etc.., the body acts just like a capacitor and
> the same goes with those Leyden jars.  These discharges can provide enough
> current to be lethal, although very rare.

The problem lies in the energy stored in the terminal.
Consider a spherical terminal with 60 cm of diameter:
Its capacitance is C = 33.36 pF
It can sustain a maximum voltage of V = 900 kV, with maximum surface 
field of 30 kV/cm.
The stored energy, 0.5*C*V^2, reaches 13.5 Joules.
The accepted limit for a not very dangerous impulsive shock is 10 
Joules.
This corresponds to a terminal with 27 cm of radius. After this,
the stored energy grows quickly, with the cube of the radius.
The stored energy can be calculated as Emax = 500.4*r^3 Joules,
r in meters.
Of course, the same applies for a Tesla coil with a terminal of
equivalent capacitance and voltage giving single discharges, with 
the aggravation that a Tesla coil recharges the terminal much faster 
than a VDG.

Antonio Carlos M. de Queiroz