E'telekeli said:

>I learned that all sources of helium on the planet are underground, and
>associated with natural gas or oil wells. How it got there to begin with
>is a mystery to me, since helium is inert and (like the equally exotic
>heavy metals) almost entirely a product of stellar evolution. I imagine:
>helium entrained as clathrates in primordial planetesimals.... was
>trapped beneath relatively impervious rock strata. Point is - helium
>is a finite, non-renewable resource.

I once believed the same thing. One day I was complaining to a friend
(who is much wiser than I) that I thought it a terrible waste to put a
relatively rare and nonrenewable resource like helium into children's
baloons. He immediately straightened me out. Helium is a continually
generated resource. It comes from decayed alpha particles emitted
from subterrean radioactive material like radon and uranium. So long as
there is naturally radioactive material in the Earth's mantle, there will
be helium produced.

Frank Luxem said:

>Addison Bain, former NASA hydrogen program manager, has determined beyond
>doubt that the airship fire was caused by ignition of the fabric cover due
>to static discharge. He obtained a sample of the fabric and discovered it
>was doped with powdered iron oxide and powdered aluminum in a matrix. Sound
>familiar? The whole darned dirigible was coated with SOLID ROCKET FUEL!
>If you look at the film, the whole outside of the ship was consumed in
>flame while it was still in the air. Eyewitness accounts all mention the
>bright orange-yellow flames. Hydrogen, of course, burns with no color at all.

This may well be true. Pure hydrogen won't burn (it needs to be mixed with
oxygen). The hydrogen was such an obvious danger that the Hindenburg's
designers probably did everything they could to make sure any leaked
hydrogen would quickly vent from its envelope. To the designers, the use of
a highly flamable fabric probably didn't seem unreasonable because the
added risk wasn't significant. I'm sure there was plenty of burning
hydrogen along with the burning fabric. This sort of danger may seem
crazy but think about what's in your car's gas tank when it's almost
empty (air saturated with gas fumes). On top of that you have an electric
device in the middle of your gas tank, the fuel level sender. The
explosive power of an empty fume saturated gasolene tank is probably
comparable to a stick of dynamite. Oddly enough, not that many people
die from exploded gas tanks.

Gary