Basis for Relative Effectiveness

[mrb314159]

Hi folks,

Does anyone know how the relative effectiveness (RE) factors for explosives are determined? Are they empirical or theoretical? I see tables of RE values constantly being used, but they never seem to be accompanies by a correct explanation of their basis. Occasionally, someone will say that RE is a ratio of the VoD of an explosive to that of TNT, but the values I compute never agree with the values given in the tables.

Thanks.

[Nails]

Does anyone know how the relative effectiveness (RE) factors for explosives are determined?


Do NOT quote entire posts! :mad:


According to wikipedia:

Relative effectiveness factor (R.E. factor) is a measurement of an explosive's power for military demolitions purposes. It measures the detonating velocity relative to that of TNT, which has an R.E. factor of 1.00.

VOD of the same chemical can vary drastically depending on purity, temp, density and a host of other variables.

[JakeGallows]

The article Nails refers to is this one:

http://en.wikipedia.org/wiki/Relative_effectiveness

Though it is a very limited subset of information about explosives. Like Nails said, there are many factors that can change VoD. In addition there are a variety of other measures used to determine the Power or Performance of an explosive. How effective explosives are is relative to what you are trying to accomplish with them. You might try reading:

http://en.wikipedia.org/wiki/Explosive

[mrb314159]

I have tried to create ratios of VoD and cannot duplicate the RE tables. I believe the Wikipedia statement is wrong. In fact, I posed the question in the hope that I could find someone who is familiar with how VoD is determined so that I could update the Wikipedia.

Thanks for the responses.

[megalomania]

How exactly do you compute your results? The determination of the vdet for explosive materials will require you to actually detonate a representative sample and a calibration standard. The standard used is certainly not always TNT! Not always I say, that does not mean it can’t be used. The problem you are encountering is a lack of both testing method and standard used.

The vdet is determined by either cameras, velocity probes, the Dautriche method, or optical fibers. The accuracy of these methods differs. There’s that nasty precision vs accuracy thing that analytical chemists love (they call it anal chem for a reason). One can assume they used TNT as the standard, but you know where that leads you, right?

Take brisance for example, in the lead block test you can use Pentrit or Ammonit as standards. Density differences and a lack of proportionality may necessitate the use of a more appropriate standard.

Due to some shortcomings, such as the influence of the charge volume when charges of constant mass are tested, the quality and the price of the lead block, and the lack of the strict proportionality between the true strength of an explosive and the lead block expansion, Belyaev has proposed the use of the so-called equivalent charge to express the strength of explosives.

In that case, the determination of the strength of an explosive is based on the determination of the mass of the reference explosive charge Ammonit-6, that produces the same expansion value as an explosive tested under the same testing conditions. Since equal lead block expansion values should be the result of equal works done, it can be written:

Ax/AAmmonit-6 = MAmmonit-6/Mx

Enlighten us, what equation are you using to compute your values, and what figures are you plugging in?

[Diabolique]

Try correlating the Pc-j (Chapman-Jouget pressure - the pressure immediately behind the detonation front) of the explosives. Very high correlation. This is related to both the density and detonation velocity of the explosive, among other factors.

This Pc-j correlation is why the explosives labs are getting away from effects relative to TNT. Many tests are also losing favor due to their expending energy in ways that do not contribute to the measurement of explosive power. Even the close-in profiles of the air shock waves from various explosives are quite different, so blast effects are not readily comparable.

Some of the most accurate measurements of detonation velocity, and indirectly, the equation of state parameters such as Pc-j, is x-ray imaging. The Phermex equipment is the current standard, time accuracy on the order of nanoseconds.

You may want to download the "LLNL Explosives Handbook" and "Introduction to the Technology of Explosives" from the ftp site. You may want to look at the Phermex texts as well. The first impression of Phermex is WTF?! until you start to understand what they are doing.

[armchairsapper]

I have a copy of FM 5-25 Explosives and Demolitions. FM 5-25 states: "Explosives vary not only in detonating rate or velocity, but also in other characteristics, such as density and heat production, that determine their effectiveness. They vary so much that the amount of explosives used is computed according to a relative effectiveness factor, based on the effectiveness of all high explosives in relation to that of TNT. For example, TNT, with a detonating velocity of 23,000 feet per second, has a relative effectiveness factor of 1, while tetrytol, with the same velocity has a higher relative effectiveness factor of 1.20."

[Charles Owlen Picket]

The reason this is an old post is that the subject matter (Basis for Relative Effectiveness) is subjective in it's relationship to the evaluation surround. One gentleman proposed utilizing the Chapman-Jouget, another brought up the relational comparison to TNT. While another brought up the whole question of relational comparison on a variety of levels in the determination of VoD as well as the rhetorical question of what foundational equation would be utilized to begin with.

The military basically uses energetic materials to destroy shit and hurt people. The mining industry uses energetics to accomplish work such as moving earth or digging. Other industry uses energetic materials to expand or open sealed or solid objects, etc, etc.

The comparisons therefore become contingent upon the surrounding evaluational dynamics. An aluminized burst charge with high heat and brisance may hurt someone viciously and be optimum for a weapon but it may fall flat when moving earth to accomplish work. The military uses TNT as a base because it exists as a consistent basis for comparison but most importantly they see explosives as weapons. The explosives industry however does not employ a strict Basis for Relative Effectiveness because they see energetics as tools.

[armchairsapper]

I’m probably going to get flamed for this since I’m new and Charles appears to have been here for a while.

The original question was “is RE empirical or theoretical” and is it based on “a ratio of the VoD… to that of TNT”. My post gave an empirical definition from a trusted source, not wikipedia aka: hearsay backed up by more hearsay. Diabolique mentioned PC-j which includes density and VoD, though very informative, did not answer the original question. The definition I found makes mention of VoD, Heat, & density.

Also… the statement “The military basically uses energetic materials to destroy shit and hurt people.” Is pretty naïve. Combat engineers make use of explosives in many of the same way as “the mining industry”. Most of FM 5-25 is formulas for cutting steal, concrete, and earthworks. Not… put some C4 in a pipe and throw it at people.

I find it hard to believe that RE depends on what industry it is being used in. Especially since a wide variety of explosives that would be used in a variety of industries all use the same RE tables. This would suggest one standard not many.

If someone posts another empirical definition of RE from another industry that is different than the one I posted I will gladly concede that I was wrong.

[Charles Owlen Picket]

Why would you get flamed? I think you just have a bit of a misunderstanding about my post is all. I was not actually addressing your statement specifically.

However if you think that statement is pretty naive, I disagree. Yes, the military DOES use explosives to build roads and dig into earth, move rocks and things similar to industry. However, compare the quantity of production and use-based implementation of the explosives that the military maintains and sets aside. Compare the very basis of the use of explosives in the military. NOT the role of the combat engineer. But the militarily use of explosives and I think you would agree that the level of explosive manufacture is to destroy shit and hurt people.

We have an enormous amount of conventional explosives as air-dropped munitions. We have quite a bit of stuff used by engineering units. Compare the amounts and field use orientation for production. ...no, not the same as Industry. Industry does not use [the same] as weapons but for specifically applied mechanical work.

NOW then addressing what your query was toward the end, re:"that RE depends on what industry it is being used in", remember that it is private sector industry (specifically, chemical engineering, explosives industry, mining) that does the research. If ICI decides that water-gels are the new TNT, that's what is used for comparative basis elements. Fair or not, logical or not, that's who makes the sales pitch (& thus the rules for evaluation). The military MAY have criteria.....But it's the private sector that closes the deal. I hope I was clear in that concept. I am not debating the merits of this issue: but the history of how it comes about. The military has never really called the shots in the US: that's why we use the term "Military Industrial Complex".

[armchairsapper]

Ok. I jumped the gun a bit. I did missunderstand some of Charles' post and I took the comment about the military personally. If you consider the amount of explosives used then yes, the majority of explosives used by the military are in the form of air dropped munitions. I thought Charles was discounting the combat engineering uses of explosives entirely.

I don't know who coined the term "relative effectiveness", the military or private sector. Charles is right that the private sector does the lions share of research. Though I still find it hard to beleive that there are multiple definitions for RE. That RE is used to describe so many different types of explosives suggests that there is one deffinition, However, I have very litle experience with explosives in the private sector so I really don't know.

[Charles Owlen Picket]

To the best of my knowledge RE is a term that is used a great deal by the military but seeps over to private sector (common enough...) and visa versa. In the explosives industry this is common and confusing. That whole realm used to be called the "powder industry" back in the time when "powder companies" had sales reps that went about, touting their wares and using sales pitches. One of which was the (famous or infamous) "pushing or heaving power" of low explosives.

There was really nothing that could not be accomplished with low explosives that could not be accomplished with HE but the powder companies had tons and tons of BP to sell. Then tragedy struck when ammonium nitrate became available. The companies saw themselves loosing a fortune and they went to work selling the idea that certain jobs needed a certain "type" of push or heave. Clay or shale need a different level of heave then coal as coal would break into too small of pieces to be of use, etc.

NOTE: this is all tongue-in-cheek BS: I don't personally believe a word that the companies say. I am still on a variety of lists to receive various trade magazines as they come out and they still have this tripe.

They had to make a play to sell off their BP. They had to start a myth that certain types of explosives had intrinsic properties that could never be supplanted by differing placement, etc. Ammonium nitrate had a very detrimental effect on their bottom line. Inventor's scrambled to develop water gels. This would take ammonium nitrate and raise the cost....it was the answer to a prayer.

Therefore they use the term (RE) and take a wee bit of fact and mix in some rumor....and the public buys it. "The last shot knocked the coal too fine. They wanted it at 2lb. blocks and it's as fine as gravel...we're in trouble". "It must have been that explosive. I couldn't have misplaced my bore holes." "NO....you're blameless...Buy this crap and you'll be fine."

The term "RE" could be a by product of the advertising blitz to make various low explosives and unwanted goods sell more effectively. I don't really know. Their slick page magazines describe relational effectiveness to sell products that don't need to be sold. The magazine Explosives Engineering is filled with advertisements for water gels. This is to make the consumer believe that there is really a difference between one "high-priced spread" and another. They are all margarine - not butter. Water Gels are a way to make ammonium nitrate sell at a profit level. When various inventors made really effective blasting products they were quickly bought out and or crushed by the giants.
To loose the market would mean that companies like DuPont would show losses. We can't have that. So anything to make a sales pitch was distorted. One of them was the concept of RE. Compare explosives to soap and you will quickly understand what I mean. If a dish washing detergent gets you dishes clean and another soap is designed for your hands, another for your floor, etc...Does that mean you HAVE to use all the various types of soap? No, it's convenient perhaps but one could wash their hands with dish soap and their hands would be clean. but if you are a soap mfg you want people to think they cannot possibly wash their hands with dish soap...it's too strong. Or their cloths; they must have a super powdered detergent with elephant snot to really clean them bla, bla.

[Zait]

The Military uses RE factors as a convienent way to replace one explosive for another in calculations.

For instance. The demolition of a bridge span requires the placement of 100 lbs of TNT at 3 locations. Unfortunately since TNT is in short supply all they have available is C-4. The theory is that by applying the RE factor for C-4 as the replacement for TNT you can calculate how much C-4 you need.

TNT required = 100
C-4 RE = 1.34

100 / 1.34 = 74.63 lbs of C-4

Again, it's theory. In reality you would do the base calculations for C-4 since you know you already have that.

It's called 'relative' effectiveness for a reason. It's not precise and outside of the military and a few civilian breaching schools it's not taught or used any more. In reality comparing explosives properties using RE factors is like comparing apples and oranges. The are both round and a fruit but making a Waldorf salad with oranges doesn't mean you will get the same result as you did if you used apples like the recipe calls for.