If there is more than one blasting cap, the device might be booby trapped to detect the broken circuit in either one and trigger the other when this happens - in which case none of the wires would be safe to cut.
Do you know of way to do that without greatly increasing the chances of the bomb builder blowing himself up? Please don’t explain how, yes or no will do.
longhair75 said:
So how much “bang” does a blasting cap have?
Mangetout said:
You’re supposing a case where the detonator is rigged or inaccessible but the plastique is exposed? Juggling the plastic may set off the detonator (you don’t know), so burn it away instead? Interesting. Works until the heat sets off the blasting caps.
silenus said:
Hollywood does this all the time. “Okay, I cut the wire. OH NO, I sped up the timer!” What would it take to make a circuit do that? How do clock circuits work?
Merijeek said:
Tell me about it! 
(So where did I spend those 4 points?)
I have had a few cases in practice where dark green looks black to me, and confusion arisen because of it. Nothing life threatening, merely annoying. One was the color of a T-shirt, another is the color of lines on a gym floor at an athletic center. Referring to “that black line over there” and getting puzzled looks doesn’t inspire confidence in your abilities as an instructor.
I believe the bridge wire doesn’t merely become hot, but explodes from the high current it experiences. More advanced detonators use an exploding piece of foil if memory serves.
As you probably know, there are also non-electrical caps but I can’t tell if they use a fuse or det-cord. BTW, how quickly will det-cord burn if you light one end with a flame?
Also, how powerful is a #8 detonator compared to, say, an ordinary firecracker?
Thanks,
Rob
I do. (Assuming I’m building the electronics from scratch, not from a watch.)
If I were designing a bomb with a visible counter, I wouldn’t make it go off when the counter gets to zero. Maybe 42. Or 13. Or 666. (Hey, if you’re going to be evil…) 
[QUOTE=Irishman;12501842
What would it take to make a circuit do that? How do clock circuits work?
[/QUOTE]
If you used the most common simple timing circuit, you would only need an extra piece of wire and maybe an additional resistor, depending on other components already needed for a simple configuration. It might take an additional $2.00 worth of parts if your circuit is more complex, bringing the total to maybe $2.10. But thats if you only want the timer to speed up. If this is the actual power source to your detontator that has been cut, then you need some other way to detontate the bomb. I am assuming you don’t mean speeding up the timer so it immediatly goes to 0 and the bomb detonatates simutaneously. What is the point of speeding up the timer anyway? Psycopathy? If I ever had to make a bomb, and I hope I never do, I would use the simplest reliable detonation circuit possible. And all of you should be following my father’s advice as well.
This is true, but it requires a much more complicated circuit than the one that blew up Sayid and the submarine appeared to be.
I can, easily, and without any extra parts, again assuming I get to build it from scratch, not from a watch.
I’m not sure why people seem to think the only kinds of electronics that can count down or display time are existing watches and clocks. Microcontrollers these days are cheap (cheaper than the circuit board they’re mounted on) and very easy to use.
Why spend all that money on a micro-controller? It’s just a timer to set off a bomb. Or maybe not, he wasn’t clear if he wanted the bomb to go off or not. He only mentions speeding up the timer. And if you are a psychopath, you’re cutting short your fun by actually detonating the bomb. If the bomb never goes off, the guy will remember that moment for the rest of his life. My father would have told you he already thought of that.
So can I. It’s not that hard. But the Bad Guy in the scenario used a common digital watch as a timer, and he was pressed for time. I wish I could find a good screen capture of the bomb in question. It didn’t look all that complicated.
49 cents is “all that money”?
The entire circuit may cost you more. But at $0.49, that would be quibbling. Ok, you would probably have to spend an additional 1/2 hour on programming. Hmm, ok, I’m convinced. But I’ve got the other thing on the bench, so it would cost me nothing! Hah!
Did I sound humbled? I am. I assumed the controller would cost you at least $1.00 after you added in shipping. Wait, did you count shipping? I’m hanging by a thread here. If you still come in under a buck, or just for nothing like me, I take my hat off to you. Good plan. Many more options, if you don’t kill yourself actually trying to do this.
Maybe there should be a thread about the best micro-controllers to be used for non-violent purposes. Honestly everybody, if you think you are going to build a bomb, you are a major league idiot.
Oh nuts, another insult. Was that indirect enough? I said if. I didn’t name anyone.
I am EOD. In the situation you describe (with minimal details in the OP), I would cut or scrape away the explosives from the detonator. Not leisurely, mind you, but I wouldn’t MacGruber around 'neither.
You want 49 cents? I give you my two.
Tripler
Very little drama ensues.
Maybe I should do an “ask the embedded systems engineer”. Not tonight though.
Well that’s good data!
The really old blasting caps used a relatively large quantity of mercury fulminate to substitute for the sensitive primary explosive and the base charge, and they were quite shock sensitive. They could fire if you simply dropped them.
Some modern detonator designs don’t contain a primary (shock sensitive) explosive at all. Instead they use a very hot pyrotechnic and burst disc to trip a secondary (shock insensitive) explosive into detonation. You could hit them with a hammer or worse quite safely, and John McClane would have been out of luck.
Exploding wire and exploding foil detonators are for specific applications where timing is critical. (Like imploding a fission bomb pit, which is the reason why exploding foil caps were developed IIRC) A normal bridge wire doesn’t have to explode, which is why a 9V battery is enough to fire a detonator.
A fuse. They are more or less the same as the electric caps but with the bridge wire taken out. You poke the fuse into the open end with the ignition compound, and crimp it on.
Det-cord is actually explosive and will initiate the charge directly. You poke the end of it into the C4 or whatever and attach a cap to your end to fire it. One advantage of this is safety - the cap isn’t placed until you’re ready to fire, and if you get a hangfire, it’s easy to see what went wrong and fairly safe to approach the unfired cap and poke it with a stick.
No idea. Not sure if it even will burn - there’s a thin thread of explosive in there (PETN or RDX) which should burn okay, but the containing tube may be enough to quench it.
Now that’s a tricky question! The effectiveness of a detonator in doing its job is a matter of how powerful a shockwave it can inject into the main charge. This isn’t just a matter of energy release but also how fast the energy is released. That “shocking power” is called brisance. A modern no. 8 with a built-in base charge releases less energy than an old fulminate no. 8 but is just as good, because PETN is much more brisant than mercury fulminate. (Historical factoid - the old “standard” detonator was the weaker “no. 6”, because the older dynamite explosives were nitroglycerine-based and easier to detonate. And an old fulminate no. 6 is STILL more "powerful’ in terms of energy release than a modern no. 8, but won’t reliably fire a brick of C4 because it doesn’t have the brisance.)
A big firecracker will probably release a LOT more energy that a no. 8 detonator. But it’s absolutely useless for detonating C4, TNT or practically any other secondary explosive, because it’s brisance is pitiful.
EXCEPT, there had to be something sneaking in there. After all, Sawyer pulled the leads and the bomb still went off.
I’m still liking the clay disassembly.
-Joe
Info worth more than that. I assume a design characteristic of C4 was lack of ‘volatility’, not sure what the proper term is there. Please tell me C4 is not that easy to get hold of.
And if I got overly vigorous, and I managed to short my knife across the two leads from the detonator…no explodey, right?
-Joe
Is the bomb on a metal surface? Any other way to close a circuit to the presumed detonation source? Then you should be ok, unless these is another level of booby trap. But if an EOD says carving away C4 is safe, do that. Also keep your knife away from where the ‘probes’ are. I assume they are actually caps, or else the caps are internally hidden in the block, maybe with something else. So avoid touching anything that isn’t C4.
“Sensitivity” is the term you’re looking for and you’re right - C4 isn’t very sensitive at all, either to shock or flame. Anecdotes from Vietnam describe people cooking over burning blocks of it like hexy fuel tabs.
C4 is ~90% RDX by weight, in a plasticising medium. You can think of it as RDX powder made into a dough by mixing with oil, although it’s a bit more complicated than that (How Stuff Works has a good article IIRC.) Its main design characteristics are plasticity and water resistance. It’s not any kind of super-powerful explosive and it may well be available for civilian demolition operations, or else a cheaper PETN-based equivalent. If you need to cut I-beams or similar explosively, it’s hard to beat the intimate contact that a plastic explosive can provide.