Detonation

[TranslucentDragon]

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.

[Mumbles]

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.

[BurritoBandito]

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.

[Peret]

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.

[schroedinger]

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.

[Mumbles]

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.

[BurritoBandito]

@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.

[HissingRDX]

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.

[Arthur]

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

[MrB]

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.

B!

[hindsight]

"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.

[HissingRDX]

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.

[FlareLauncher]

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

[pyrocoyote]

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.

[MrB]

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.

B!

Edited January 23, 2015 by MrB

[patsroom]

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

[MrB]

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!

[pyrocoyote]

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

[DrJones]

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?

[ronmoper76]

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/get-tr-doc/pdf?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 March 16, 2021 by ronmoper76

[ronmoper76]

i also have a book that talks ALOTt about detonating flash,with and without blasting caps...IM HUMBLY ASKING THE SAME THING?

[ronmoper76]

The Significant factor here is that 23% of the incidents RESULTED IN SOME

FORM OF AN EXPLOSION, since pyrotechnic compositions are not normally

considered to be explosive in nature." [Emphasis added.] Of interest were the

TNT equivalence (Hi Explosive equivalence) tests. Of the six compositions used

for producing sound two were tested for TNT Equivalence with the following

results: Air Blast Simulator Mixture, as used in the M74A1 and M74 Simulator.

[Aluminum flake 9%, Black Powder 91%] TNT Equivalence was found to be

45%. Detonation Simulator Mixture, use: the infamous M80. [************] TNT

equivalence 80%. It should be noted that; "The M80 fire cracker mixture is no

longer manufactured but is reported along with the test data BECAUSE OF

SEVERAL CATASTROPHIC ACCIDENTS THAT HAVE OCCURRED." [Emphasis

added.]

"Critical Height" and "Critical Diameter" were also measured. "In the critical

height test the "Critical height to explosion data are reported as the greatest

material height in a given container diameter which did not result in transition

from burning to an" explosion.

Critical diameter tests the sample material using C4 as an explosive donor, to

determine the minimum diameter required to induce a explosive reaction.

The critical Diameter for the M80 composition was found to be 0.01 meters [4

inches!!!]. and the Critical Height was measured as being 3.96cm. [1.5 inches!!!]

[Fools rush in where angles fear to tread.]Of the photoflash mixtures tested, TNT

Equivalence of: 30-36-50% were measured. And even closer to homer a Yellow

Star Mixture [Magnesium 18%, Barium Nitrate 17%, Strontium Nitrate 16%,

Potassium Perchlorate 17%, Sodium Oxalate 17%, and HCB 12%] when tested:

"indicated that this mix would detonate and an explosive equivalence (as

compared to TNT) was greater then 50% in a contained vessel ***" This mixture

was also found to be sensitive to friction and impact.

Propagation Rates In Thermally Ignited Pyrotechnic Compositions. Richard W.

Collett, Tech Report ARLCD-TR-77049, August 1978, NTIS ADA060809.

"Work was performed to determine the propagation rates in loose, granular

confined pyrotechnic compositions when initiated thermally. Representative

materials included flash, igniter and flare compositions."All compositions were

tested confined in steel pipe 48" long by 2"id. both ends of which were sealed

with heavy end caps. An igniter pack placed in the bottom of the column was

used for thermal ignition.Conclusions: "All of the compositions tested developed

fast reactions which could cause explosions and be extremely hazardous ***.

The reactions are therefore all classed as detonative." [Emphasis added.]

Of the four basic compositions tested, PFP-555 [Aluminum 15u 40.0%, Barium

nitrate 140u 30.0%, and Potassium perchlorate 20u 30.0%] "can develop either

a low-velocity or high-velocity detonation when thermally ignited. Test 1- 920

meters/sec. Test 2-546 meters/sec."

Explosive Power of Pyrotechnic Compositions. 1.M. Jenkins, Et. All, 19th

Explosives Safety Seminar, Calif. 1980 Page 77 &ff.

"Various pyrotechnic compositions were assessed in three experiments:

1-To measure and assess the explosive power from various initiating stimuli.

2-To measure the explosive power expressed in terms of the equivalent mass of

TNT per unit mass.

3-The likelihood and effect of sympathetic initiation in a practical storage

situation."

Three initiating stimuli were used: 1/fuzehead 2/electric detonator, and 3/a

detonator boosted with a tetryl pellet. The composition being placed in a paper

mache pot, with the initiator being placed at the geometric center of the charge

mass.

Composition #11: Photoflash [40/60 Aluminum/Potassium Percolate] when

ignited by source number three, resulted in an "equivalent mass approximation

kg. TNT per unit mass" of 0.42. More rigorous testing using piezo-electric

pressure transducers to measure air blast and other experiments using foil

gauges raised the TNT equivalence to 50%.

TNT Equivalencies of Black Powder. Volume 1: Management Summary and

Technical Discussion, H.S. Napadensk and J.J. Swatosh Jr., lTIRJ6265-3,

Sept. 1972, NTIS ADA-044444. 69 pages + vii.

"Black powder charges ranging in weight from 8 to 150 pounds were evaluated

under different levels of confinement. The TNT equivalence for the final product

were found to range between zero to 43% for impulse and zero to 24% for

pressure, depending upon the level of confinement, the weight of explosive and

booster, and the distance form the explosion."

The generally quoted figure for the detonation velocity of BP is 400 meters/sec.

However A.F. Belyaev and RKh. Kurbangalina; Russ. J. Phys.Chem. 38:309-

310,1964, as quoted in the LLNL Explosives Handbook, URCL-52997, provide

the following figures Density g/cm3 appx. 0.7, det velocity appx. 1.3 km/cm3,

1.35 km/sec.

Hazards Testing of Ammonium Perchlorate. F.L. McIntyre, et al, 58 pages. NTIS

ADA-114966

A series of hazard classification tests were conducted on ammonium

[tenneyguy]

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.

 

I believe your last sentence is right on the money. For example, detonable smokeless powder is "burned" in small arms ammunition, among others, WITHOUT detonation, which CAN occur, and does cause devastating results. Typical burn rate vs pressure curves for smokeless show a peak pressure following which pressure begins to drop. This illustrates it's use as a propellant for projectiles (bullets). Such curves are based on increasing volume behind the projectile and increasing velocity of it, thus halting burn rate increase,in order to illustrate the PEAK pressure reached as it applies to the particular application.

 

In the event the burning commences in a rigidly confined volume, the burning rate will increase exponentially very quickly, possibly until "something gives". Thus the use of smokeless powder as propellant depends on the burning rate never reaching that "point of no return" pressure. If it does, ruptured barrels, damaged gun mechanisms, and possible injury result.

 

It may be said then that smokeless powder MAY detonate under certain conditions whereas black powder will not.

Edited June 15, 2021 by tenneyguy

[tenneyguy]

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.

 

TNT detonation rate = 23,000 feet per second, very fast. 10 times the speed of a common rifle bullet.

[FlaMtnBkr]

On the topic of smokeless powder, double base smokeless is not only NC but nitroglycerin as well. I believe Bullseye has the most NG @ 40% if I remember correctly, which isn't a negligible amount. And obviously burns instead of detonates based on the very few shattered barrels and/or receivers. And of those few I think most are linked to material imperfections, excessive age and/or use, or an obstructed barrel and not because of an 'earth shattering boom' aka detonation.

 

I'm far from an expert but it's been my understanding that a detonation happens when a shockwave travels thru the material at sufficient speed/energy that molecular bonds are broken releasing a tremendous amount of energy almost simultaneously. And no heat, flame, or oxygen is required as with burning, and many times there are no visible flames. This is why Tannerite detonates because the bullet is traveling fast enough to impart enough energy to start the bond breaking. When it burns there is heat/flame and oxygen and the material/fuel heats and destructively oxidizes like a normal fire which lacks the necessary energy to break the molecular bonds that releases the explosive energy.

 

In something like flash powder the particles are very small with lots of surface area so burns fast like a small piece of tissue paper vs a log. And it also has its own oxygen supply and isn't slowed down by having to use what's in the air which is consumed and takes time for more to move in and replace the supply. Without the limits a very fast burn results, releasing lots of energy in a small instant. Metals also burn hot and higher temperatures result in higher pressure which increases how fast it burns which is also why containment can be important to allow greater pressure. And in some cases the chemicals involved can burn fast and hot enough to release enough energy to start breaking those energetic molecular bonds which adds more energy and it turns into a detonation thru the rest of the material, which is the deflagration detonation transition (DDT - where deflagration means burns really really fast).

 

At least this is my layman understanding of it all...