The limit between high and low explosives?

[Iñaki]

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]

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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[Iñaki]

I think you´re 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 (I´m 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 ´cause power makes people ambitious, and the ambition is what´ll make that stable explosive to blow up at an unthinkable moment...!" - me

[Mr Cool]

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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[Iñaki]

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, it´s a unique molecule (assuming that in the compound there´s 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 ´cause power makes people ambitious, and the ambition is what´ll make that stable explosive to blow up at an unthinkable moment...!" - me

[BoB-]

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]

Isnt propagation of a explosve faster than 1000 m/s considered detonation?

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[CodeMason]

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]

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]

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]

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]

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]

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]

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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Go here (http://briefcase.yahoo.com/nbk2ooo) to download the NBK2000 files and videos.

[Microtek]

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]

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]

ANFO a low explosive?!? Uhm, I don't think so.

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[Microtek]

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]

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]

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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[CodeMason]

<font face="Verdana, Arial" size="2">I tend to think of high explosives as explosives that can't undergo their intended steps in their chemichal decomposition without exploding.</font>Who's intended steps? The government's? This is not true, as many high explosives can quietly burn (TNT, nitro to lesser extent) and decompose fully, and others will decompose when say, dissolved in a solution of KOH and boiled.
<font face="Verdana, Arial" size="2">Could it be something to do with the total ammount of energy</font>Thermite puts out more energy than black powder, in the form of heat, but thermite doesn't explode.

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[EventHorizon]

Someone please correct me. I was unaware that black powder actually detonated. I thought it only deflagrated and that self confinement was around 550 pounds.

I beleive I've read a publication that had the correct definitions of high and low explosives. I'll search through what I have and see if I can find it.

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[CodeMason]

Black powder certainly doesn't detonate.

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[PYRO500]

I know that many high explosives can burn, I ment by intended steps by what hapens when they are initiated, such as BP gets burned, the BP had chemicals that react with each other that the chemichal reaction is the same when you initiate it correctly, something like TNT I don't think follows the same chain of chemichal reactions when burned as when it detonates, I could be wrong, but that's my idea.

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[MacCleod]

It seems we may be comparing apples and oranges here,folks.I'm sure there's a scientific definition to differentiate between low and high explosives.But there's also the 'what it's used for' factor,which nbk pointed out.For making anti-personnel grenades low explosives work fine (bp,flash,etc.),but if your intent is to topple an electrical tower,7000+ mps is a must.I always classified HE's as one's that could shear metal/rock,and LE's as anything less powerful than that.Pretty generic distinction,I know,but in the proper context I think it makes sense.Let the vod fit the crime!.

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[cutefix]

Remember also that certain high explosives can exhibit both low and high detonation characterisitics.A particular example is Astrolite G.If you initiate it with a weak blasting cap(#4-#6) it will undergo only low VOD(around 2000m/s) but if boosted(with #8 or higher,) it will exhibit high VOD(above 8000 m/s).

[Microtek]

The technical definition of high explosive behaviour is detonation; if it detonates then it's a high explosive.
One of the big guns at alt.engr.explosives said in one of their many discussions that just about any energetic material can be detonated if it is initiated with sufficient power. In the case of black powder, the detonation probably wouldn't be self-sustaining, but it was simply an example to illustrate a point.

[Mr Cool]

People keep saying "If it detonates then it's a high explosive." Well that hardly helps, does it? Not unless you go on to define detonation, which is really what this argument is about or at least it appears that way to me.
I'll clarify my definition a bit: the fuel and oxygen must come from the same molecule in an HE. Basically what someone else was saying...
I have no idea what I'd call chlorate/vaseline, chlorate/MNN etc!! I'd have to call them low explosives, in which the decomposition is propagated via shock rather than heat. But apart from things like that, my definition normally seems to work, from a theoretcal/scientific point of view.
Someone here suggested petrol was an LE; this is wrong, petrol is simply flammable since it needs an external source of oxygen. Petrol vapour in air could be a low explosive IMHO, since the air/vapour mixture doesn't need oxygen from the air... it gets complicated, I'm confusing myself with my own definitions now so I can't really be helping you much!

If I had my way I'd introduce a new class - Medium Explosives.
LE's would be mixtures of compounds that burn, and must build up pressure to explode, e.g. BP, Benzoex. They can be set off by shock, but the decomposition wave is not self sustaining.
ME's would be mixtures of compounds that can be set off, without confinement, by a blasting cap and/or fuse and have a self-sustaining decomposition wave travelling faster than the speed of sound, producing a report, e.g. Chlorates/MNN, KClO4/P.
HE's would be pure compounds that can be set off with a blasting cap or fuse and have a decomposition wave travelling faster than the speed of sound, e.g. TNT, RDX. HE's could be mixed with other compounds to improve performance or reduce cost, such as Torpex or Ammonal.

I think we can conclude from this that the definition of an LE or HE is up to you, since everyone seems to have a different idea!

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[CodeMason]

Then Mr Cool, what kind of explosive is nitrocellulose? If it clearly deflagrates and behaves as a LE when ignited by fuse, but has the fuel and oxidizer radicals on the same molecule? This is another exception to your rule, not to mention Astrolites, etc.

A high explosive detonates. Detonation is defined as the propagation of deflagration faster than the speed of sound.

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[Iñaki]

Then, codemason, do u think black powder really detonates? if confined, bp can reach 340 mps easily and more, but i don´t think it really detonates. Taking it from the encyclopaedia definition, "detonation is an extremely fast decomposition of an explosive within a shock wave, with speed from 1 to 9 kms" and "deflagration is a fast combustion, propagated thermically, and can change with confinement from milimeters/second to several decameters/second"

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

[Iñaki]

this is why i agree with madscientist´s definition of detonation and deflagration (shockwave one and thermal the other one) although high speed deflagrations may reach speed of sound and even "catch" low detonations, for the "explosive" molecules the reaction is completely different from the "deflagration" ones, and i think it can be seen in many characteristics like VoD, the energy released by weight, temperature of gases in explosion, the volume of these gases and pressure that can reach. although this is only my point of view

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

[Microtek]

I think the problem here is simply that our area of interest is simply too varied for us to be able to be exact with a blanket statement. I doubt there are many here that would be in doubt whether an explosion was high or low if given a specific example; it's the generalized definition that is the problem.

[Mr Cool]

I would say that NC was a highly flammable high explosive, which exothermically decomposes when heated in confinement into water, CO2 etc etc, like many HE's would.
Astrolites would be high explosives in my definition, I don't see why you think they're unusual. They're basically just hydrazinium nitrate.

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[CodeMason]

Ok, I retract my "speed of sound" definition, I was getting feet mixed up with meters! :P

Mr Cool:
<font face="Verdana, Arial" size="2">I would say that NC was a highly flammable high explosive</font>Highly flammable? But above you said, something is merely flammable if it burns but cannot supply its own oxygen (or other oxidizing molecule, if you want to get technical).
<font face="Verdana, Arial" size="2">which exothermically decomposes when heated in confinement into water, CO2 etc etc, like many HE's would.</font>Many HE's and LE's both fit this definition. You said if it had the oxidizing radicals on the same molecule it was a HE, even though nitrocellulose clearly exhibits more of LE properties.
<font face="Verdana, Arial" size="2">Astrolites would be high explosives in my definition, I don't see why you think they're unusual. They're basically just hydrazinium nitrate.</font>They're a mixture of primarily hydrazinium nitrate and ammonia dissolved in hydrazine. The NH₃ (to a lesser extent) and NH₂NH₂ are the fuels. Hydrazinium nitrate possesses very few of Astrolite's explosive properties when on its own. It doesn't have fuel/oxidizer radicals on the same molecule, and yet it is a clear HE with performance close to RDX.

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[EventHorizon]

As stated in my 28.11.01 post, I've found the book I thought it was in.

From the Blasting and Explosives Safety Training Manual:A guide for the Industrial Blaster, published by Eastside Service Company, low explosives are classified as having rates of detonation below 3,280 fps (1,093.33 m/s) and high explosives having a VoD of 3,280 fps or greater.



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[Mr Cool]

"quote:
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which exothermically decomposes when heated in confinement into water, CO2 etc etc, like many HE's would.
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Many HE's and LE's both fit this definition. You said if it had the oxidizing radicals on the same molecule it was a HE, even though nitrocellulose clearly exhibits more of LE properties."

So what if HE's and LE's both decompose when heated? That statement I made was not in my definition, so your first sentence is irrelevant. I didn't say that having oxidising and fuel radicals on the same molecule automatically made it an HE, I just said that all HE's did.

"They're a mixture of primarily hydrazinium nitrate and ammonia dissolved in hydrazine. The NH3 (to a lesser extent) and NH2NH2 are the fuels. Hydrazinium nitrate possesses very few of Astrolite's explosive properties when on its own. It doesn't have fuel/oxidizer radicals on the same molecule, and yet it is a clear HE with performance close to RDX."

In my definition of an HE, I did say that the HE could be mixed with other substances to improve detonation characteristics, such as OB, VoD etc. And since Astrolites are mainly hydrazinium nitrate, which detonates alone, I class them as HE's. Most methods I've seen for making astrolite say to let it stand for a while. Therefore, most of the ammonia produced will come out, and most of the hydrazine will be used to make hydrazinium nitrate, so neither the free ammonia or free hydrazine help much anyway.
Hydrazinium nitrate does have many characteristics of Astrolite, such as a very high VoD. And the fuel and oxygen in HN are contained in the same "molecule" (it's ionic, thereofre that word is incorrect but you know what I mean). So it fits into my HE definition very nicely.
Or, if the HN was being used as an oxidiser for the NH3/N2H4, then it would fit into my medium explosives class, since my definitions did not depend upon VoD or power, merely the type. The names could perhaps be misleading in some cases.

And anyway, if you don't like my definitions then fine, don't use them! I didn't expect anyone to, I was just saying what I thought.

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