## Detonator / booster size vs main charge

Grantr - 30-11-2015 at 06:21

How do you determine how strong of a detonator/ booster you need for a given sized main charge? Is this more or less found by trial and error?

If a 1 gram ETN detonator sets off a 1/4 pound charge of say TNT, should I expect a 1 gram ETN detonator to set off a 5 pound charge of TNT?

No I do not have TNT this is just in theory and since TNT is somewhat hard to set off. I am trying to understand the dynamic behind how it works.

[Edited on 30-11-2015 by Grantr]

szuko03 - 30-11-2015 at 08:53

I am pretty sure that as long as the force is high enough to start the "shock wave" through the compound that wave will propagate through the entire mass regardless of the size as it is continued by the substance itself. I am not exactly sure but that's how i always viewed it.

The only issue may be if the substance itself blows apart by the shock wave and fragments before it can be propagated though.

careysub - 30-11-2015 at 14:24

 Quote: Originally posted by Grantr How do you determine how strong of a detonator/ booster you need for a given sized main charge? Is this more or less found by trial and error? If a 1 gram ETN detonator sets off a 1/4 pound charge of say TNT, should I expect a 1 gram ETN detonator to set off a 5 pound charge of TNT? No I do not have TNT this is just in theory and since TNT is somewhat hard to set off. I am trying to understand the dynamic behind how it works. [Edited on 30-11-2015 by Grantr]

If a 1 gram ETN detonator can set off a 1/4 pound charge it can set off a one million pound charge. Once the detonation wave is established in a self-sustaining way in the main charge it will propagate forever.

OneEyedPyro - 30-11-2015 at 21:05

Many HEs can go low order without adequate initiation, with smaller charges ANFO can go high order from a weak initiatior but with a large charge you'll get a partial/low order det.

It really all depends on the explosive in question, some will accelerate to full detonation velocity with insufficient initiation while others will undergo a partial det.

[Edited on 1-12-2015 by OneEyedPyro]

Grantr - 1-12-2015 at 05:25

Thanks guys.

Interesting you say any HEs can go low order without adequate initiation. I knew that Nitroglycerin would do that.

I have noticed Ammonal mixed at a 97% AN to 3% AL ratio has a much louder detotation and stronger shockwave when set off with .5 grams of ETN vs being shot with a rifle. Also a rifle will not set it off with a 90/10 ratio while ETN will and being mixed at that ratio is quite a bit stronger with more aluminum.

Why does ANFO behave differently in larger quantities? I did try a 40 gram ANFO charge in a ziplock bag. .5 grams ETN only partially set it off. Nothing remotly close to 40 gram ammonal.

careysub - 1-12-2015 at 07:09

For nearly all explosives capable of undergoing detonation ("high explosives") there is a critical size of the explosive mass required to create a self-sustaining detonation wave.

This is usually measured by the critical diameter of an unconfined column of explosive that will maintain a constant velocity detonation wave. If the diameter is less than the critical size even establishing a detonation with a strong initiation will not create a self-sustaining wave , it will slow down, weaken, and die out. The energy lost from the sides of the column is too great.

ANFO has a very large critical diameter, so small quantities will not sustain a detonation well. Large driving charges relative to the main explosive are required to achieve nearly complete detonation. Not a problem in the blasting applications in which it is employed, though the loading bore holes do need to have adequate diameter.

Confinement of course helps.

Some explosives can detonate in extremely small quantities. The well known primary explosives are examples of these, which is largely what makes them useful in that role.

A technical discussion is found here:

http://www.dtic.mil/dtic/tr/fulltext/u2/a106485.pdf

[Edited on 1-12-2015 by careysub]