[AR] Re: Mythbusters panel at Comicon mentioned a "myth" I've heard in "r...
- From: Norman Yarvin <yarvin@xxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sat, 2 Aug 2014 08:50:17 -0400
On Fri, Aug 01, 2014 at 01:10:43PM -0700, Ray Rocket wrote:
>On Fri, 8/1/14, Norman Yarvin <yarvin@xxxxxxxxxxxx> wrote:
>> how is it that you get enough intermixture between asphalt and LOX
>> to actually have a serious explosion?
>
>Answer #3: asphalt thermal shrinkage and micro-cracking with prolonged
>LO2 exposure could be a mechanism to greatly increase surface area and
>wick LO2. Also note the dissimilar thermal contraction rates between
>asphalt and aggregates is likely to create voids. This could be
>tested with LN2, by measuring sample weight and size, with final
>verification via LO2 impact tests.
Consider, though, that this is how they harden glass: by suddenly
quenching the outside of a near-molten piece. (I think asphalt is
close enough to melting for the analogy to apply.) The outside
freezes hard while the inside is still soft; then once the inside
freezes, you have compressive stress baked into the outside, the
inside being under tension. This increases the resistance to
cracking. Or, well, sometimes the piece to be hardened just shatters
when quenched. And after being hardened, if you hit it hard enough it
shatters. So the process definitely produces baked-in internal
stresses which could aid in cracking, but (if the glass analogy
applies) it won't be micro-cracking; instead it will be large-scale
cracking, and that usually after a whack.
>Thanks for the excellent report, I didn't know it existed. The report
>doesn't correlate LO2 exposure/cold soak times with reactivity, that
>would be an interesting read.
It is JMKrell who is to be thanked for posting the link.
From reading it, the magnitude of the danger didn't seem to be all
that great: the report was written to investigate some occasional
reports of explosion, which from the responses of experts who were
polled didn't sound like they were all that common. And in their
experiments, the way they got their final big bang was to bury an
aluminum block to act as an anvil, and put a mass of asphalt rubble on
top of it -- neither of which they had done before. It's the kind of
thing you do if your attitude is "dammit, we've gotten some bangs out
of this apparatus, but no really good bangs; let's get a really good
bang before we call it quits". And it wasn't like they'd been using
too little material to produce a big bang: they had been using 2-foot
squares of asphalt, covered with a continuous layer of LOX. That's
enough fuel and oxidizer to produce quite a devastating explosion,
were it all to react. Even their final big bang didn't result in
their test apparatus being destroyed nearly as thoroughly or scattered
nearly as widely as a complete explosion would have done; and their
previous experiments, though producing bangs, hadn't injured the test
apparatus.
Not that the danger should be ignored, of course; if you're specifying
a pad where a LOX spill is likely, make it concrete; and under normal
circumstances, if you get a LOX spill on asphalt, stay away from it.
But if something large is about to explode, and the fastest way out of
the area is to drive over a road that LOX has spilled on, that's
probably the way to go.
--
Norman Yarvin http://yarchive.net/blog
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