Re "Shell shock" for veterans or current service people or 
those involved with rocketry or explosives.
Liable to be of enough interest to a few here to be worth 
posting.
Also of interest to terminally infected engineers in 
general.

People at Mojave Spaceport were diescussing having carried 
out mukltiple rocket firings in one day recently. Up to 400 
in once case. The great Henry Spencer said:


On Fri, 21 Mar 2008, Ben Brockert wrote:
> >  >I fired a rocket engine over 400 times today, and am a 
> > bit shell shocked.
> >  What, you weren't wearing hearing protection?  :-)
>
> I was, but hearing protection or not everything still 
> jitters.

A note of caution here, guys:  this is not something to take 
lightly.

Quite by coincidence, I was just reading an article that I'd 
meant to
mention here, although in connection with explosions rather 
than noise.

In the 25 Jan 2008 issue of Science (yes, I'm a bit behind 
on reading),
page 406:  "Shell Shock Revisited:  solving the puzzle of 
blast trauma".
There is increasingly strong evidence that exposure to the 
blast wave from
an explosion can cause significant, long-lasting brain 
injury even in
people who show no obvious physical wounds.  Precisely how 
that happens is
still somewhat unclear, but EEGs and brain scans have now 
documented the
injuries beyond serious doubt.  "Shell shock" is real, it's 
nasty, and it
often doesn't go away.

Danger signs are having been unconscious or dazed from the 
blast,
difficulty remembering events just before it, and 
development soon after
of headaches and impaired reaction time and concentration. 
Ongoing
symptoms can include those plus insomnia, vertigo, and 
memory problems.

This one isn't just some anti-war alarmism; the US military 
is taking it
very seriously.  The field medics in Iraq and Afghanistan 
now check
soldiers who've been in a blast for brain-injury symptoms, 
and the VA is
doing brain-injury screening on *all* Iraq/Afghanistan 
veterans who come
to its hospitals for anything.  (The sticky question of such 
injuries from
earlier wars hasn't yet been addressed seriously.)  Current 
estimates are
that 10-20% (!) of all troops returning from 
Iraq/Afghanistan have taken
some degree of brain injury.  R&D effort has been stepped up 
sharply, in
hopes of developing better tests, better treatment, and 
hopefully better
protection against it.

                                                           Henry 
Spencer
                                                       henry@zoo.utoronto.ca
                                                       (henry@spsystems.net)


________________________

And then:

On Sat, 22 Mar 2008, David Weinshenker wrote:
> > Quite by coincidence, I was just reading an article that 
> > I'd meant to
> > mention here, although in connection with explosions 
> > rather than noise.
> > ...
>
> Was there anything that would lead to useful on 
> correlating danger
> levels between explosion overpressures and rocket sound 
> pressure levels?

No, this piece was solely on explosion-caused trauma, which 
is obviously
itself of some relevance to experimental rocketry -- which 
is why I'd been
meaning to post something about it.  Ben's informal 
reference to "shell
shock" just made me think of it.  On the other hand, if a 
single strong
shock wave can cause injury, it's not unthinkable that 
prolonged exposure
to milder pressure waves could...

> For that matter, is there any quantitative data available 
> for blast
> trauma thresholds yet? How much of an idea do they have 
> about what level
> of blast wave pressure is involved to produce the sort of 
> injuries in
> question?

This piece didn't go into a lot of detail, but my guess 
would be that
nobody has good numerical data yet.  They're just begun 
experimental work
on animals to try to establish the underlying mechanism, 
which would tell
them which variables are important.  (One suggested 
mechanism was
analogous to car-collision whiplash, but preliminary 
indications from the
first animal tests are that restraining head motion doesn't 
help.  The
major alternative theory right now is that the shock wave 
propagates up
the major blood vessels from the torso, which would help 
explain why the
symptoms suggest injury to *interior* regions of the brain, 
whereas the
usual whiplash injuries tend to hit the outer layers.)

                                                           Henry 
Spencer
                                                       henry@zoo.utoronto.ca
                                                       (henry@spsystems.net)



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