Model Forum / General / Rockets / November 2006

AP and APCP are two very different things.

-- Roger

Duh,

   That is AP powder not "Ammonium Perchlorate Composite Propellent"
Sure it can explode but so can coal dust and grain dust.
Try and get a pile of APCP grains to explode.  Big fire, but it
won't detonate.

AP is an oxidizer.  I don't see how it can explode by itself.

I seem to recall that one AP plant explosion was fueled in part by the
asphalt underneath the AP and in another case a natural gas pipeline under
a pile of AP.

I might be remembering things incorectly.

Brian Elfert

AP is not APCP.

That detonation occurred only because of very specific conditions that
existed at that particular place and time.

1) Large quantities.
2) Heat induced decomposition of AP reduced the density within the
storage bins.
3) A shock input started the detonation.

This was discussed at length in an issue of HPR magazine many years ago.
This was the Tripoli members only "Crash and Burn" issue. Well worth the
reading if you can locate a copy.

But back to APCP. Most formulations, with obvious exceptions for things
that have additives like HMX and such, are "zero card". That is that
they can be placed next to a detonator and fail to sustain the detonation.

Very large quantities might be able to detonate. But how much do you
need? The report submitted by the ATF that shows testing on the shuttle
propellant doesn't support detonation. That report discusses what the
linear shaped charge used for thrust termination does to the propellant.
It doesn't explode or detonate. Mild burning.

On 17-Nov-2006, "Fred Shecter" <fred.e.shecter@zorch.alum.zorch.mit.edu>
wrote:

Sorry I took your mistake correcting as an affront to my detonation comment.
Just for info,  I just cut and pasted that sentence from the web page that
had the video.  I should have removed the rocket fuel part of the sentence
(didn't even think about it).  I've taken my blood pressure med's so I am a
bit less sensitive as I was earlier.

Thanks,
KT

I think I finally realized what many of you were trying to tell me.... The
sentance that said:

would tend to imply that AP was a rocket fuel.  It just dawned on me that
this is what the reply posts were trying to tell me.  Why didn't ya'll speak
more clearly...  Any way,  that sentance I just copy & pasted from the web
site that had the video.  I did not even think to remove or correct the fuel
part of it to say oxidizer.  However,  I did add the (ammonium perchlorate)
because I was thinking the same thing.

Just wanted to apologize for getting all worked up.  I just got a little
defensive.  My wife had to remind me to take my blood pressure meds
(seriously,  I was almost to the point of detonation!)  So I took them and
now I can see more clearly what yall tried to tell me.

Thanks,

KT

A lot of confusion here, but I'll take a whack at clearing it up.  Yes,
APCP can detonate.  This is not news.  All of the ballistic missiles
launched from submarines can detonate or are shock sensitive.  The
reason is that nitroglycerin is added to the propellant to up the
specific impulse.  The launch tubes make the missile volume limit so
maximum specific impulse is required for the desired range.  These
types of AP propellants are called "Double Base".  Some types of APCP
propellants use an energetic binder that can make the propellant shock
sensitive and detonate.  Often an energetic plasticizer is added to not
only "thin out the mix viscosity", but to increase the specific impulse
and/or burn rate.   These energetic plasticizers, even with an inert
binder, can make the propellant shock sensitive.  All of the propellant
types above are used by the military, not in hobby rocket motors.

Your video was of an AP factory blowing up.   AP by itself is shock
sensitive.  It becomes more sensitive as the AP particle is decreased.
90 micron AP is the smallest particle sized shipped under DOT
regulations,  Small AP particles are too dangerous for transportation
on public highways or railroads.   Simply dropping a drum full of very
small AP particles can cause the drum to detonate.  Again, this is well
known to users of AP as the AP MSDS sheets discusses all of this.  In
industry, a simple bimodal mix of AP particle sizes is 10 to 1.   200
micron AP is bought and then it is ground down to 20 microns to get the
10 to 1 ratio.  This is done remotely as it is not unusual for a grind
station to blow up during this process of grinding.

Ok, how can it be that AP which is shock sensitive by itself, (i.e.,
can be made to detonate by hitting it with a hammer) be put into a
propellant and not have it be shock sensitive.  The answer is the
binder.  In very simple terms, it is like a "rubber cushion" around
each particle and provides a barrier or shock dampener to a detonation
wave from getting started in the propellant.  The effectiveness of the
binder in making the propellant non-detonable is measured using a "card
gap test".   Again, in simple terms, a sample of APCP propellant is
impacted by a projectile fired at a known kinetic energy.  Cards are
placed between the projectile and propellant sample such that the
projectile loses kinetic energy as it passes through the cards.  The
first test would be with zero cards.  If the projectile does not cause
the propellant to detonate, then the propellant is considered
non-detonable and extremely safe.  This is the case for hobby
propellant.  If the propellant detonates, then cards are added until
the projectile loses sufficient energy as it passes through the cards
such that the propellant does not detonate upon impact.   This is the
card rating of the propellant.   Based on the rating, the propellant is
classified as the 1.1 (detonable) or 1.3 (non-detonable propellant).
The dividing line is 70 cards or (70 kbar input shock pressure).  What
that means is that propellants 70 cards and under are considered 1.3
propellants or non-detonable.  However, as we just discussed a 30 card,
10 card and 50 card APCP will detonate even though they are rated
non-detonable.  But, hobby propellant is rated as 0 cards, which means
it has not detonated under the tests, not even once.

Finally, the 60 inch rule of APCPs detonating.  I have heard this, too.
However, I can not find anything to back it up.  Once you understand
the mechanics of what is going on, it makes even less sense.  What is
really being discussed here is the distance required to set up a
detonation wave.  For example, ammonium nitrate or AN by itself has a
detonation wave distance of about 8 inches.  That means it takes a
solid particle of AN 8 inches thick to just start the detonation wave,
assuming sufficient impact force has been imparted to cause detonation.
I can easily envision an APCP formulation that could set up a
detonation wave in one inch, 20 inches, 50 inches, 60 inches, 130
inches or take your pick.  It would depend on the formulation, particle
sizes, etc.  The bottom line is that there is no rule of thumb of 60
inches for all APCP formulations.  I could easily make an APCP
formulation that could be 500 ft long and you will not get it to
detonate.

This has been long winded, but perhaps the differences between one APCP
and another APCP begin to come through.  There is no one APCP fits all
or rules of thumb. The problem is the ATFE has decided one APCP does
fit all and they picked the APCP that detonates as the one that fits
all.   The injustice is that the hobby APCP does not detonate.  So, the
TRA/NAR suit's complaint against the ATFE is accurate and not a waste
of time.  If the ATFE was really interested in correcting this
injustice rather than just trying to save face, they would more exactly
define which APCP are on the explosives list.  This could easily be
done by the number of cards in the card gap test.  They would not have
to accept 70 cards. They could use a lower number or make it zero
cards.  I proposed this approach to them, but received no reply.

John Wickman

Detonation and failure of the motor casing are two very different
things.

I can overpressurize a tank with steam and have it catastrophically
fail, taking most of the building with it.  This doesn't mean steam can
detonate.

On Nov 17, 12:30 pm, kimba...@pacbell.net wrote: