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#1 TranslucentDragon

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Posted 02 February 2014 - 01:43 AM

So I've been reading conkling's Chemistry of Pyrotechnics and read a footnote in the book that said that high explosives can burn if put under a flame, but won't explode? This confused me because I thought the only way they could be ignited was via a detonation (the activation energy it takes to release the energy in the compounds could only be achieved with a shock wave). How is this possible? What happens in a detonation chemically to a compound, that doesn't happen with a deflagration? How can something that can cause an explosion of epic proportions simply just burn? Also, I'm not sure if this should be discussed in this section due to HE, but I had assumed that because I'm referring to detonation and the chemistry behind detonation, and not actually making or manufacturing HE, that it would be ok. Please tell me if I'm wrong.
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#2 Mumbles

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Posted 02 February 2014 - 01:50 AM

Different decomposition pathways.  There are several common examples that will burn if lit with a flame.  Some compositions however are capable of a DDT, which despite a common misconception, is not shorthand for detonation.  It stands for deflagration detonation transition.  The materials that are capable of a sustained stable deflagration need to be initiated with a shockwave.  This starts off a chain reaction of a different pathway that usually will release more energy, and be self-sustaining.  This is just postulation, but I suspect some of the reactions needed to induce a detonation are pressure dependent. 


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#3 BurritoBandito

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Posted 08 February 2014 - 10:19 PM

Isn't the basic idea just that a shockwave propagates through the explosive at supersonic speeds as opposed to the energy being carried by a flamefront, and since the wave is traveling faster than the speed of sound the peaks are cascaded? Some HEs will deflagrate when burned unconfined, but as mumbles said can undergo a DDT when enough of the material is present to "self confine". I agree with your assumption, mumbles, that some of the reactions are pressure dependent. The self confinement seems to be due to the substance being confines by it's own mass. An assumption on my part would be that more dense HEs would self confine with a smaller volume of material present. I think it is that the increase in pressure/density allows the material to propagate the wave better.
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#4 Peret

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Posted 09 February 2014 - 02:22 AM

From a quick look round on the web, there appears to be a lot of disagreement and confusion about what constitutes detonation. The guy who wrote the Wikipedia entries seems to be particularly confused. For me, it's only detonation if it propagates by the shock wave first, with the chemical reaction following. Any reaction that propagates only chemically is deflagration. Flash powder self-confines, but it doesn't detonate. It propagates chemically, by fire. It does go pretty fast, though, something in the order of 2000 ft/sec. That's less than any true high explosive, but it's comparable. I think TNT goes around 6000 ft/sec.


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#5 schroedinger

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Posted 09 February 2014 - 03:02 AM

TNThas a VOD of 6900m/s so much faster. If it is a detonation depends on mutiple factors. A Detonation propagates by shock wave and is fast compared to the speed of sound. A deflagration is slow compared to the sound and does propagate by chemical reaktion. But there is an error often done. Reaktion in gasses are often just defined on the propagation speed. I don't have table at hand atm. but it basically labels propagation speeds into three different parts. First slow propagation with a propagation of couple hundred meter per second. Explosion with moderate speeds And detonation with high speeds. The detonation allready started somewhere sonic and double sonic speed This tabel is often also used for solid substances. And from this table flash detonates, as part of the sound flash produces is done by burning faster then the inner sonic speed is.

#6 Mumbles

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Posted 09 February 2014 - 05:33 PM

The speed of sound thing has nothing to do with the speed of sound through air.  Many compositions are capable of burning faster than the speed of sound through air.  Flash powders and whistles can burn several times faster than the speed of sound through air, and even BP is capable of exceeding it.  This has nothing to do with what constitutes a detonation.  The defining factor is that the shockwave propagates faster than the speed of sound IN THE MATERIAL.  Given that most of the things we're talking about are solids, this is typically well in excess of 2,000 m/s.


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#7 BurritoBandito

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Posted 09 February 2014 - 05:43 PM

@Mumbles: Understood... Im not sure if this statement was directed to my post, but I was referring to the speed of the wave traveling through the material as well. This is why I was saying that the pressure and density help the wave to propagate (through the material itself, not the air). Perhaps I should have been more concise in my explanation of my thoughts.

The speed of sound thing has nothing to do with the speed of sound through air.  Many compositions are capable of burning faster than the speed of sound through air.  Flash powders and whistles can burn several times faster than the speed of sound through air, and even BP is capable of exceeding it.  This has nothing to do with what constitutes a detonation.  The defining factor is that the shockwave propagates faster than the speed of sound IN THE MATERIAL.  Given that most of the things we're talking about are solids, this is typically well in excess of 2,000 m/s.


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#8 HissingRDX

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Posted 13 April 2014 - 09:18 PM

No, denser HE's will not be more susceptible to DDT, if this was the case, then C4 or even TNT would explode when burned, instead a slow and steady flame is observed. 

 

Density of most High Explosives plays a major role in determining it's VOD, detonation pressure etc. and vise-versa. With the exception of material like TNT which decomposes w/ lack of Oxygen, hence it's lower VOD than what might be thought for a Carbon, Nitrogen, Oxygen, Hydrogen explosive, and AN which has an ideal overall density for performance based on fuel and compositions. 

 

A shockwave cannot travel through a material faster than the detonation front itself, VOD can also be thought of as velocity of decomposition.



#9 Arthur

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Posted 14 April 2014 - 12:05 PM

A HE can and may decompose by shockwave, but some can also burn slowly, and some can transition from burning to detonating. 



#10 MrB

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Posted 15 April 2014 - 06:14 PM

No, denser HE's will not be more susceptible to DDT, if this was the case, then C4 or even TNT would explode when burned, instead a slow and steady flame is observed.

I'm not sure i agree with slow and steady. At least C4 has a kind of violent feeling to it's fire, TNT i don't know about.

What i mean is, slow and steady is something like a candle, where as C4 behaves more like a fanned woodfire, the flames are a lot wider then the burning C4, and higher then, well, expected.

Oh. And don't step on it, trying to put it out. It will smear, and keep burning unless you get it just right. Having a burning goo all over the sole of your shoe, is a invite to set the whole shoe on fire.

 

C4 is a great firestarter due to it's intense heat, and energetic burn, and can be used to heat canned foods and stuff like that. I'd rather use firewood, but since it's also pretty much smokeless, it helps if you want to remain undetected. The smell was... interesting. If you knew what it was, you'd probably recognize it from some distance, but it wasn't unpleasant.

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#11 hindsight

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Posted 15 April 2014 - 07:30 PM

"C4 is a great firestarter due to it's intense heat, and energetic burn, and can be used to heat canned foods and stuff like that. I'd rather use firewood, but since it's also pretty much smokeless, it helps if you want to remain undetected. The smell was... interesting. If you knew what it was, you'd probably recognize it from some distance, but it wasn't unpleasant." B!

 

MrB, you amaze me.  A "certain diplomatic advisor" to the NVA, made sure that part of their training was to learn the smell of C4 burning as fuel ... for tactical reasons.



#12 HissingRDX

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Posted 15 April 2014 - 07:56 PM

Yes I take that back for C4 burning slow and mellow, it sounds like you have military experience. What does burning C4 smell like? I think the smell would be the burning of the oil, plasticizer or binder in the composition. 



#13 FlareLauncher

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Posted 28 April 2014 - 06:08 PM

Burning C4 came with a caution, as I recall (it's been a while) not to shave the pieces you were using too thick....



#14 pyrocoyote

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Posted 23 January 2015 - 03:08 AM

C4 fumes are very poisoness when burning.  TNT is very dirty when burning. They will as a lot of HE will, det when burning. But it takes a volume of weight on itself to do this. We never stacked more than 2 thick 112 blocks when we destroyed it with fire ( yes we burned a lot of it in pit ) because of the weight of the stack on itself,  burning it can explode. TNT in large amounts will explode when burning. When we would RSP, say a 500 lb general perp bomb we would place a penterator charge and most times that starts the HE comp to burning. once the flame starts to burn so intense with pressure from hole in case the HE would explode with low order or sometimes high order. The pressure within the case with burning HE is the cause. HE gets very pissed off when it burns. Heating c-rats with c4 was reason for more than enough ambushes because of the smell.


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#15 MrB

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Posted 23 January 2015 - 09:51 AM

C4 fumes are very poisoness when burning.  TNT is very dirty when burning. They will as a lot of HE will, det when burning. But it takes a volume of weight on itself to do this.

I'm not going to say "you are wrong" since i simply don't know. But if C-4 is to detonate from it's own weight while burning, then your talking truckloads of it, and i just don't see it happening. Simply put, you can put it on fire, let it burn, and if your stupid enough, go hit it with a sledge hammer. It will shoot burning sticky stuff everywhere, but it wont detonate. The pressure from the hammer head when impacting is a lot higher then any pile of C-4 i've ever seen would introduce to the stuff in the bottom, so if there ever is a detonation risk from burning it, i doubt it's from the weight... And we never took any safety precautions other then "don't let the fire spread" when burning the stuff.

 

Toxic fumes... Well, lets put it like this. I'd rather inhale fumes, then eat the stuff. Neither is good for you, but... Sick-leave, you know? People do it all the time.

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Edited by MrB, 23 January 2015 - 09:51 AM.


#16 patsroom

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Posted 23 January 2015 - 03:57 PM

In Vietnam My brother said that the Supply Sgt. just could not understand why all the claymores were  being used for in  my brothers unit. So someone told him (the supply Sgt.) that they use the C-4 in the claymore for heating their c-rations. Well the Supply Sgt. just looked at them and say something like " if you are going to use it for cooking then just order C-4 blocks instead". True story..............Pat



#17 MrB

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Posted 23 January 2015 - 04:10 PM

Makes sense. The claymores are freaking expensive in comparison to the C-4 thats in em. No reason to set fire to the whole block of C-4 to heat ya dinner either, so it lasts a lot longer...

B!



#18 pyrocoyote

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Posted 20 February 2015 - 11:03 AM

Next time I destroy a volume of plastic I will stack about 8 high and video it for you. Seeing is beleiving.


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#19 DrJones

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Posted 15 March 2021 - 04:33 PM

Someone wrote on this topic: "Flash powder self-confines, but it doesn't detonate." I humbly beg to differ, and have read references that from 5-gm to 20-gm lots of flash can, do, and will detonate. Comments?



#20 ronmoper76

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Posted 16 March 2021 - 07:45 AM

Why does it say ALL OVER THE WEB that flash burns between 4000 and 6000 feet per second,(i just double checked to make sure my memory isn't playing tricks}  I found 4 references in a matter of two minutes that say otherwise...Could someone please explain that for me? Am i misinterpreting it somehow? Why does your flash burn slower than the rest of the world?

 

All rise the WiZard speaks.

"the M80 firecracker mixture had an
equivalency of approximately 80%."

NB — For AIR BLAST.

Accession Number : ADA096248
Title : A Compilation of Hazard and Test Data for Pyrotechnic Compositions
Descriptive Note : Final rept. Jan 69-Mar 79
Corporate Author : COMPUTER SCIENCES CORP STENNIS SPACE CENTER MS
Personal Author(s) : McIntyre, Fred L ; Rindner, Richard M
Report Date : Oct 1980
Pagination or Media Count : 384

Full Text : http://www.dtic.mil/...df?AD=ADA096248

As the late Big Bruce noted in American Fireworks News Chemical explosives many years ago ... you cannot blow bank vault doors w/ M80's. Chemical compositions lack Brisance.

Brisance /brɪˈzɑːns/ is the shattering capability of a high explosive, determined mainly by its detonation pressure. The term can be traced from the French verb "briser" (to break or shatter) ultimately derived from the Celtic word "brissim" (to break).

PLEASE the word is French and is not pronounced bristant. The eponymous Fresnel light house lens is also French and is not pronounced as spelled. The the eponymous SI unit of work or energy the Joule is also French and not pronounced Jowel.

Practice on this isochronous (a technology that buttered my bread for many years.)

Hint it is from the Greek. Hint two — for reasons not given to me to understand in English we use a hard C rather than a K, e.g. zinc (German/French zinK.)

The TNT equivalency is for the original border line suicidal potassium perchorate/sulphur/antimony trisulphide/aluminium mixture. This comp was replaced w/ the standard potassium perchlorate/aluminium comp.
The current comp used is black powder/aluminium I would posit the same comps used in the Air Burst Simulator Projectile Mixture 91% black powder 9% aluminium.

I explained this more detail in my American Fireworks News article. I am tempted to post it, however, I am currently hiding form the County Pervert Posse, my laptop does not have this file on its HD.

Suggestion too .... when disusing explosive do not use the term "power" used w/explosives it has a v/ technical meaning. I am sure 99% of the great unwashed masses here do not know the details


Edited by ronmoper76, 16 March 2021 - 07:53 AM.





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