Re: breakdown of hydrogen

To: tesla-at-pupman-dot-com
Subject: Re: breakdown of hydrogen
From: "Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Wed, 12 Jan 2000 17:52:21 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Gas breakdown data: http://home.earthlink-dot-net/~jimlux/hv/insulgas.htm
Hydrogen breakdown is roughly 0.65 that of air at same temp and pressure..
so, about 19.5 kV/cm..

explosion risk is actually quite high...

Hydrogen has the widest flammability range of any gas when mixed with air
(BTW, acetylene is a close second)... It also has a low ignition energy (so
it's easy to ignite the mixture with a small (static) spark).

The saving grace is that it is so light (i.e. not dense), that if it leaks
it goes right up to the ceiling, and hopefully away from ignition sources
(which would tend to be benchtop level).  Unlike, say, propane or gasoline,
which are quite dense and form "pools" of vapor in low spots as traps for
the unwary.

The other significant problems with hydrogen:

1) It leaks through anything.  The diffusion mobility is quite high, so the
tiniest crack is a significant leak source
2) The flame is perfectly colorless, and has no radiant heat. You could have
a huge hydrogen flame burning next to you, and except for the noise, you
wouldn't know it is there.  There are documented cases of people walking
into large hydrogen flames stemming from an accidentally ignited leak. As
you might imagine, the results are quite unpleasant.  The traditional safety
precaution is a straw broom.  You walk with the broom held in front of you,
and if it bursts into flame, you stop walking.
3) Hydrogen embrittlement is a  problem with high pressure hydrogen
handling.

That all said, hydrogen is great stuff in a spark gap. It has a very very
fast quenching time, so you can get high rep rates. It has high thermal
conductivity (low mass..) and low viscosity (in absolute terms) so it is
used to cool high speed turbogenerators (for example).  Just be aware of the
risks.. ventilation is key.

-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Wednesday, January 12, 2000 2:41 PM
Subject: breakdown of hydrogen


>Original Poster: Mike Nolley <mnolley-at-mail.slc.edu>
>
>    Can anyone tell me the breakdown voltage of hydrogen at STP?
>            I'm in the middle of designing a hydrogen gap.  I've heard that
>since hydrogen has such a low density the risk of hazardous explosion when
it
>is mixed with air is very low.
>
>
>