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Re: [Phys-L] Not a shock wave in Beirut.

On 8/10/20 6:35 PM, bernard cleyet wrote:

Wow, nice article. It explains a lot of the observations.

I saw the Subject: line and immediately gave myself a dope-slap.
I already had plenty of evidence to support that conclusion, but
I didn't connect the dots.
— As bad as it was, the Beirut explosion could have been a lot
worse. Relatively speaking, there were remarkably few fatalities,
given the amount of explosive and the population density.
— Relatively speaking, there was a lot less property damage than
there could have been.
— Ammonium nitrate can be either a low explosive (burning, push)
or a high explosive (detonation, !BANG!) depending on details,
and in this case I couldn't figure out what was the initiator
that set off the detonation. Turns out there wasn't one. Duh!

Background: Gasoline is in the same category. In a piston engine
detonation i.e. knocking aka pinging is highly undesirable. Even
then, most of the fuel just burns and only the last few percent
detonates. Very destructive.

Similarly gunpowder in the same category. Hence the difference
between a gun (push) and a pipe bomb (!BANG!). Confinement makes
all the difference in this case, just as an overly-high compression
ratio leads to pinging in an engine.

NOTE: The Alfred P. Murrah attack *was* a detonation, i.e. *did*
produce a shock wave, because the attacker arranged to make it so.
I can explain how, but maybe not on a public list.

The 1947 Texas City explosion involved some confinement. So it
maybe detonated like a pipe bomb. Or maybe not. Ammonium nitrate
is not particularly easy to initiate. I have not researched the
facts on this incident.

Historical note: The distinction between low explosive (push) and high
explosive (detonation, !BANG!) has long been recognized. The distinction
between primary high explosive (always detonates) and secondary high
explosive (detonates only when properly initiated) is relatively new.
This is what made Alfred Nobel rich and famous. People say he invented
dynamite, which made nitroglycerin less sensitive, which I guess is true,
but the other half of the story is the invention of the *blasting cap*
which makes the dynamite detonate /when you want it to/. Without that,
there is no point in inventing dynamite. The key idea is to have huge
quantities of secondary high explosive, which is relatively safe to
handle, plus a tiny amount of primary high explosive, i.e. the blasting
cap, which is relatively easy to keep secure until you're 100% sure
everything else is ready. In other words, the fundamental breakthrough
is the invention of *initiation*.