Sciencemadness Discussion Board - Detonator protected from ESD

Detonator protected from ESD

Spartan - 26-3-2015 at 06:24

Hey guys, i know that primary explosives are sensitive to human static. Is it possible a primary explosive go off from human body discharge when it is inside an aluminum tube? If so, why commercial caps are made from metal and not from plastic? (as electricity can not pass plastic).
Also is it a good idea to cover aluminum tube with electrical tape?

Thanks guys and sorry for my bad english.

Metacelsus - 26-3-2015 at 07:15

Metal tubes will cause electricity to flow through the metal and not the primary. Another reason for using metal is mechanical strength.

PHILOU Zrealone - 26-3-2015 at 10:05

Static electricity will develop charges on the outer surface of the metal, because of charge repulsion --> never inside!
You should not expect thunder bolt inside a metalic box from external static electricity... a bit the same as Faraday's cage effect.

[Edited on 26-3-2015 by PHILOU Zrealone]

magneet - 26-3-2015 at 14:57

Lets turn it upside down, would static build up from some type's of plastic detonator casing affect certain primairy's?

[Edited on 26-3-2015 by magneet]

[Edited on 26-3-2015 by magneet]

Spartan - 26-3-2015 at 18:01

Hey magneet, i'm not sure about this. Maybe yes if there is a very sensitive explosive to ESD like lead styphnate inside?

PHILOU Zrealone - 27-3-2015 at 08:38

Quote: Originally posted by magneet

Lets turn it upside down, would static build up from some type's of plastic detonator casing affect certain primairy's?

[Edited on 26-3-2015 by magneet]

[Edited on 26-3-2015 by magneet]

If the primary is loose powder inside a plastic detonator that is prone to easily make static electricity build up...then yes shaking the detonator vigorously will build up static energy potential and may result in initiation...just as much as the friction and shock of the primary crystals against each other...so you may not be sure initiation comes from the static electricity!

If the detonator is done with due caution (against static when filling), well packed, with a plastic prone to static build up; then external friction of the detonator will not propagate the static charges to the interior of the detonator... Static electricity remains on the external insulated surface and this can remain very local area. You of course know the glass rod and paper experiment...when the glass rod is frictionated with wool at the end...static remains on that end and doesn't propagate to the rest of the rod...
--> So there is no risk of initiation of the primer by external static.
If the plastic is not prone to static build up... there is even less chance for this to happen.

[Edited on 27-3-2015 by PHILOU Zrealone]

magneet - 27-3-2015 at 13:10

Quote:

Maybe yes if there is a very sensitive explosive to ESD like lead styphnate inside?

I think it could be dangerous yes, when filling it with the wrong kind of dowel, (plastic prone to static) rubbing the inside when pressing

Spartan - 27-3-2015 at 14:21

A guy in an other topic named 'mabuse' put silver acetylide double salt in alluminum foil and then he shock it with the spark from a piezo electric lighter and it fired as he said. Why can not happen the same with a spark from the human body?

http://www.sciencemadness.org/talk/viewthread.php?tid=17122&...

aga - 27-3-2015 at 14:27

Cardboard is amazingly good.

It is at the same time an insulator, and a weak conductor.

Morgan - 27-3-2015 at 15:01

"Any insulating material is likely to be static-generating. One problem with cardboard and paper is that they are very variable materials and their electrical properties vary with air humidity by several orders of magnitude. Under humid air conditions they could be dissipative but under dry air conditions they could be insulating and cause a problem. So, unless you have specific ESD grades, it is better to keep them out of the ESD Protected Area."
http://electrostaticsolutions.blogspot.com/2007_10_01_archiv...

aga - 27-3-2015 at 15:59

More accurately, better to use materials best suited to your local environment, and not to forget where you are.

In many places cardboard is OK. Other places not.

Morgan - 27-3-2015 at 16:28

I vaguely remember reading something about static from two large sheets of paper. It was in some book, an old account from the 1800's or so. It was in a book like "Homemade Lightning" or something like that dealing with static electricity and electrical phenomena before electricity was mainstream. The very large sheets of paper were held next to a fireplace to get all the moisture out but I can't remember the details of the spark generation, if the sheets were separated or what.

magneet - 28-3-2015 at 03:51

Quote:

A guy in an other topic named 'mabuse' put silver acetylide double salt in alluminum foil and then he shock it with the spark from a piezo electric lighter and it fired as he said. Why can not happen the same with a spark from the human body?

Maybey the Al foil is so thin that the entry point of the spark into it locally heats up enough to initiate it?

Spartan - 28-3-2015 at 04:38

Quote: Originally posted by magneet

Quote:

Maybey the Al foil is so thin that the entry point of the spark into it locally heats up enough to initiate it?

Yes, it may be the heat from the spark that initiates it, as the alluminum foil is so thin. As he said it was not a very scientific setup...

[Edited on 28-3-2015 by Spartan]

[Edited on 28-3-2015 by Spartan]

[Edited on 28-3-2015 by Spartan]

Spartan - 29-3-2015 at 04:55

Hey guy after much thought i thought that if you have two detonators one with thin metal and one with thick metal, with the same primary explosive inside and the same external electric spark, the primary in the thick metal tube is more difficult to detonate from external spark because a big part of the electric energy absorbed through the thick metal, the thinner the metal the easier to detonate.
It's the same like you have a battery and a bulb, if you connect them with thin wires the bulb turns on, but if you use very thick or very long wires the bulb doesn't turn on because a big part of the energy absorbed through the wires.

So i think that a primary is possible to detonate inside a metal tube from human static but it depends from the thickness of the metal, the type of the metal and of course the type of primary explosive.

Here is a pdf with the sensitivity of the most common primary explosives to ESD,heat,shock and friction.
file:///C:/Users/dimitris/Downloads/9783642284359-c1%20(4).pdf

Oxydro - 29-3-2015 at 05:10

First of all you are completely wrong about the wires scenario. Thicker wires will always help transfer the electricity more easily. The only way in your scenario that the bulb will not light is if you use very long and thin wires, with so much resistance in the wires that not enough current flows to light the bulb.

The difference between thick and thin metal in this case is not really the electrical properties, but thermal. A very thin tube could potentially spot heat to a high enough temperature to ignite what's inside, with a sufficiently strong spark, whereas a thicker tube will distribute the energy through a larger mass, preventing the temperature from rising enough.

And by the way, you have included a local link to a file on your computer, not the file itself. Only someone on your computer could use that link to open the file.

Spartan - 29-3-2015 at 06:21

Quote: Originally posted by Oxydro

First of all you are completely wrong about the wires scenario. Thicker wires will always help transfer the electricity more easily. The only way in your scenario that the bulb will not light is if you use very long and thin wires, with so much resistance in the wires that not enough current flows to light the bulb.

The difference between thick and thin metal in this case is not really the electrical properties, but thermal. A very thin tube could potentially spot heat to a high enough temperature to ignite what's inside, with a sufficiently strong spark, whereas a thicker tube will distribute the energy through a larger mass, preventing the temperature from rising enough.

And by the way, you have included a local link to a file on your computer, not the file itself. Only someone on your computer could use that link to open the file.

I am sorry the link is this:
https://www.google.gr/url?sa=t&rct=j&q=&esrc=s&a...

Yes you are right you can light a bulb with thick wires. Anyhow we agree that the thinner the metal the easier to initiate the primary with external electric spark.

[Edited on 29-3-2015 by Spartan]

[Edited on 29-3-2015 by Spartan]

[Edited on 29-3-2015 by Spartan]

Static

MineMan - 29-3-2015 at 10:32

I am very interested to anything else someone might like to add, as this is much harder to prevent and conceptualize than mechanical stimuli. I have heard that if there is an air gap (even a micron) in the aluminum shell ( whether this be from foil, or fuse and aluminum contact) that static could still find it's way in. Can anyone confirm this? Are there any inert materials that can be mixed with the primary to reduce the risk?

Spartan - 30-3-2015 at 09:34

Quote: Originally posted by MineMan

I am very interested to anything else someone might like to add, as this is much harder to prevent and conceptualize than mechanical stimuli. I have heard that if there is an air gap (even a micron) in the aluminum shell ( whether this be from foil, or fuse and aluminum contact) that static could still find it's way in. Can anyone confirm this? Are there any inert materials that can be mixed with the primary to reduce the risk?

Even metals can hold some static electricity, but not so much as plastic.I don't know if this static is enough to initiate a primary explosive.

I haven't heard that even one micron gap can cause static but it may be possible. Even if it is like that i think that this static is not enough to initiate the explosive. I'm also interested if anyone knows something about this.

Laboratory of Liptakov - 3-4-2015 at 09:05

Mineman, Spartan, Magneet. This is true, what he writes Philou Z and aga. My opinion is that you deal with nonsense. The big danger (always) is pressing the detonator. A particular thorn removal. 10,000 times. Filled (closed) metal detonator explodes not. Certainly not from the human body tension. Maybe, if you use the Van der Graaf generator. I have not heard explosions from hand contact after closed detonator. But from filling yes. And not one more... :cool:

...LL

gregxy - 3-4-2015 at 10:46

I would think the greatest danger form esd would be if you are carrying the detonator by its wires or fuse, you body is charged, and the detonator case touches something that is grounded. The charge on your body will travel through the wires/fuse into the primary, through the case to ground setting off the primary. I don't know if normal fuse is conductive enough for this to happen. Connecting one of the two wires to the case would prevent it.

markx - 3-4-2015 at 13:54

Quote: Originally posted by Laboratory of Liptakov

Mineman, Spartan, Magneet. This is true, what he writes Philou Z and aga. My opinion is that you deal with nonsense. The big danger (always) is pressing the detonator. A particular thorn removal. 10,000 times. Filled (closed) metal detonator explodes not. Certainly not from the human body tension. Maybe, if you use the Van der Graaf generator. I have not heard explosions from hand contact after closed detonator. But from filling yes. And not one more... :cool:

...LL

I agree on the part of pressing...the forces at play in this step are immense compared to anything the initiator may see in the following course of its life. Any mishandling is a featherlight touch compared to the assembly pressing step. Hence I never press primaries on top of secondary, only separate carriers that are joined with secondary afterwards without any strong forces being applied.
On the part of static being nonsense I strongly disagree...static is a devil in disguise and there is not really any reasonable means to cancel it out completely. A lot depends on the particular primary used....silver compounds (azide, SADS) tend to be more suceptible to static. Grounding yourself properly, wearing cotton clothes and avoiding work in low humidity conditions are your best allies against the danger of static, but still, accidents can happen, so be prepared.