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Iņaki
November 25th, 2001, 06:23 AM
I have read in many texts that the difference between low and high explosives is the VoD, being less than 914 m/s for low ones and more than 914 to several kilometers second for high ones. So i asked myself why this number separates high from low explosives, does it have anything to do with the speed of sound? Or it is because someone liked this number (ha ha)? Thanks a lot

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nbk2000
November 25th, 2001, 07:10 AM
My own personal definition of a high explosive is 6,000+ M/s.

This covers RDX, PETN, NG, TNT, ANNM, Picric acid, and all the others like them. Basically, if it's used by the military to take down a bridge or fill a bomb, it's a high explosive.

Below 6,000 covers blasting agents like ANFO, Blasting dynamites, Black powder, and the primary explosives used for initiators (AP, Mercury Fulminate, others). If it's used by industry for quarrying or demolishing buildings, it's a low explosive.

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Iņaki
November 25th, 2001, 07:30 AM
I think youīre right, because there is no comparation between the destruction that an high explosive (RDX,C4,Picric acid...) with a low explosive (AP, mercury fulminate) can make (Iīm assuming that they are compressed and similar mass/volume). But i think that then we should have two kinds of low explosives, because there is also a big difference between the power of AP, ANFO , mercury fulminate... and for example black powder, potassium clorhate and others used in firecrakers. Am i right? Thanks

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"Nowadays this kind of knowledgment implicates power, but careful īcause power makes people ambitious, and the ambition is whatīll make that stable explosive to blow up at an unthinkable moment...!" - me

Mr Cool
November 25th, 2001, 09:30 AM
Compared to RDX, ANFO and ammonia dynamite etc. are pretty feeble, but they're definately HE's!!
But I suppose I do see your reasoning...
My definition (dunno how scientifically correct it is) is that a high explosive must meet two criteria: it must need no confinement to explode (pressure build up is instantaneous, or the rate of decomposition is greater than the speed of sound, so a bang occurs with no confinement); and it must have at least one component that can explode independantly of the rest. For example, even though KClO4/red phosphorous makes a healthy bang when set off by a small charge with no confinement, I'd still call it an LE since the two ingredients must be mixed to do this, so it doesn't undergo the usual decomposition/recombination of the compound like HE's like RDX do. ANNM, however, is an HE by my definition because the NM and AN can detonate wether mixed or not, but they are mixed to give more desirebale characteristics. Similarly, NG/sawdust etc. are HE's, because the NG can detonate alone, but the inert ingredients are added to stabilise it.
Maybe my way of thinking is just weird though.

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Iņaki
November 25th, 2001, 02:38 PM
as far as i am concerned i treat ap as an high explosive although is detonation velocity (3500m/s i think, although it depends on the confinement), and as mad sayd, itīs a unique molecule (assuming that in the compound thereīs only tricycloperoxiacetone). I see the answer depends on the point of view of each one

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"Nowadays this kind of knowledgment implicates power, but careful īcause power makes people ambitious, and the ambition is whatīll make that stable explosive to blow up at an unthinkable moment...!" - me

BoB-
November 25th, 2001, 03:34 PM
High explosives detonate, low explosives deflagrate, thats the difference. Vod or Velocity of Detonation doesnt apply to low explosives because they dont detonate.

In other words; Anything capable of detonation (even partially) is a high explosive.

From Websters;

detonate \Det"o*nate\, v. i.
To explode with a sudden report.

deflagrate \Def"la*grate\, v. t. (Chem.) To cause to burn with sudden and sparkling combustion, as by the action of intense heat.


[This message has been edited by BoB- (edited 11-25-2001).]

ALENGOSVIG1
November 25th, 2001, 03:38 PM
Isnt propagation of a explosve faster than 1000 m/s considered detonation?

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CodeMason
November 25th, 2001, 04:06 PM
There are no clear boundaries, but I think the accepted definition is deflagration below 1km/s = low, above = high. (Detonation is merely fast deflagration, just as an acid is just a weak base.) However, what if there is an explosive that burns at 900m/s if compressed to a certain density and 1100m/s if compressed to another? What would we call it, a medium explosive? http://theforum.virtualave.net/ubb/smilies/wink.gif
nbk: Your definition is not quite feasable in the scope of things. For example, if I wanted a "LE" to put in my nap charge, would you recommend ANFO?
madscientist: Nitrocellulose is both a compound and a definite low explosive (ok, ok, a HE too).

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Anthony
November 25th, 2001, 04:12 PM
I'd go with the deflagerate/detonate definition. Because you can apparently get pyro comps that burn faster than mach1 (producing a report with no confinement), but they're still very much low explosives.

mrloud
November 25th, 2001, 11:15 PM
I have a BBC documentry on video that explains the difference between HE and LE. Basically: what Bob- said.
Low explosives simply burn very fast. It is the propagation of the flame through a highly inflammable substance like black powder or petrol. In a high explosive it is the propagation of a shockwave through the substance that triggers a chemical reaction. That is why you can put a pile of BP on an anvil and hit it with a hammer and it won't ignite. Do the same thing with a stick of dynamite and you won't be so lucky. This is also why you need detonator caps. They are a small, weaker explosive that is easy to set off, but powerful enough to trigger a self perpetuating shock wave in the main charge.

CodeMason
November 25th, 2001, 11:28 PM
Some clear high explosives deflagrate (ANFO, chlorate/vaseline).
And mrloud, so only HE's are impact sensitive? Then what about chlorate/phosphorus, etc.?

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mrloud
November 25th, 2001, 11:38 PM
That was just an example of two explosives. Perhaps it was a bad one. Although, just because a substance can detonate doesn't mean it can't deflagrate and vice versa. Isn't this what the whole "can DBSP detonate?" argument is about? We know it can burn but the big question is: can it also detonate?

CodeMason
November 26th, 2001, 05:33 AM
When low explosives especially black powder are confined they don't detonate, they still deflagrate, but unlike unconfined, the pressure and heat liberated is mostly concentrated internally, making the blast when the confinement is overcome more violent. This is demonstrated with black match. In the open, this fuse will burn relatively slowly, as the heat is diffused mostly into the surroundings (re: second law of thermodynamics). In quick match, several strands of black match are confined within a straw or thick paper. The heat cannot diffuse fast enough into the surroundings for it to burn slowly, it concentrates all forwardly, which further ignites the blackmatch, thus it burns almost instantaneously. This is even more spectacular when a piece of blackmatch is tied into a simple slip knot, BANG!

madscientist, that last definition was good. Deflagration is propagated by reaction front, detonation is propagated by shockwave.

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nbk2000
November 26th, 2001, 05:38 AM
DBSP will detonate if initated with a detonator. Otherwise it just burns (deflagerates) real fast.

Anyways, even though "technically" things like chlorate/vaseline are high explosives because they detonate, rather than deflagerate, you'll never get me to call it a high explosive.

I'll stick to my "military utility" definition of low/high, thank you very much.

And ANFO is a low explosive, but it's at the higher end of the low scale.

Also, remember, that the high end of explosive energy is constantly going up. That means the gap between such low explosives as BP and ANFO, as compared to the high end explosives like CL-20 and ESN, is constantly getting bigger.

100 years from now, explosives like ANNM will be considered low explosives, just as BP is today.

Oh yeah, DBSP is a HIGH explosive (6,700M/s)when initated with a detonator.

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"I have begun evil, I shall end evil. That is the end that awaits me."

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Microtek
November 26th, 2001, 07:19 AM
I think it would be more appropriate to consider the actual decomposition as high- or low-order. As someone mentioned, many energetic compounds can undergo detonation under the right circumstances, and in these cases you would have to term it a high-order decomposition, but that doesn't mean you would call it a high explosive. Similarly, RDX and other definite HEs are used in propellant where they certainly don't detonate.
The defining characteristic of high explosive decomposition, is detonation according to most texts I have seen.
Detonation is characterized by the reaction products travelling in the same direction as the reaction zone whereas in deflagration they move in the opposite direction.
As a rule of thumb, high explosive decomposition can occur when wet, but deflagration cannot.

SawedOff8gaugeman
November 26th, 2001, 11:19 AM
I think low/high explosives definition has nothing to do with deflagration/detonation, but VoD. That's because most explosives, BOTH low and high, can be detonated OR burnt. For example, black powder has a quite high VoD, even though it lacks power.

CodeMason
November 26th, 2001, 03:11 PM
ANFO a low explosive?!? Uhm, I don't think so.

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Microtek
November 27th, 2001, 03:43 AM
When you term an explosive as low or high, you are referring to the behaviour when it is applied in the usual manner. For instance you could pack some black powder in a pipe under strong pressure and confinement and initiate it with a heavy-duty booster and it would probably detonate, but you still term BP a low explosive because that is how it is usually used. RDX is called a high explosive rather than a rocket propellant because it was more often used as a HE.
The reason I prefer to label the decomposition of any given explosion as high- or low-order is that labeling the material is often not accurate.

PYRO500
November 27th, 2001, 05:56 PM
I tend to think of high explosives as explosives that can't undergo their intended steps in their chemichal decomposition without exploding.

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mongo blongo
November 27th, 2001, 06:13 PM
Could it be something to do with the total ammount of energy (in joules,locked up in the substance) produced in the formation of the products when decomposing? or the total energy output if you will.

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