Bomb Disposal (need answer fast!! j/k)

[BeepKillBeep]

I’m wondering about the reality of a couple common tropes in TV/movies.

1 - How accurate is it to have a bomb where cutting one wire defuses the bomb but cutting any other wire (or at least the wrong wire) will blow it up?

2 - How accurate is it to have a bomb where cutting a wire causes the timer to speed up?

3 - How accurate is it to have a bomb where cutting a wire stop the timer?

Thanks in advance and umm… no pressure but I could kind of use an answer in the next 5 minutes and 3 sec … 2… 1… umm… yeah soon. (again just kidding)

[engineer_comp_geek]

1 - How accurate is it to have a bomb where cutting one wire defuses the bomb but cutting any other wire (or at least the wrong wire) will blow it up?

Most bombs are very simple and don’t include booby traps like that.

There have been some exceptions over the years, but they are rare. In WWII for example, the Germans started adding booby traps to some of their bombs so that if the bomb didn’t explode for some reason, attempting to diffuse it would set it off and kill anyone in the vicinity. This led to a bit of an arms race of sorts between the German bomb engineers and the British UXB (unexploded bomb) units. In this case the German engineers were specifically making the bombs difficult to diffuse just to add to the terror factor of the weapons.

By comparison, this is an FBI reconstruction of one of Ted Kaczynski’s (the Unibomber) bombs.

Note how simple the construction is. If you can get the bomb open to where you can look at it, figuring out which wire to cut is easy.

2 - How accurate is it to have a bomb where cutting a wire causes the timer to speed up?

Practically impossible. Timers generally have some sort of time base built into them. They are almost never regulated by external wiring.

3 - How accurate is it to have a bomb where cutting a wire stop the timer?

Why on earth would you try to stop the timer? Cut the wire leading to the detonator. Then it doesn’t matter what the timer does. If the detonator is disconnected, the bomb ain’t goin’ kablooey. Period.

Real world bombs also rarely include custom-made 7-segment display timers.

Fancy timers and cutting the red or blue wire are all plot devices designed to heighten drama. Real world bombs aren’t made that way.

Cutting wires would also be a last resort for a modern bomb disposal unit. They can have a robot pick up the bomb and put it into a bomb-proof container, then take the bomb somewhere safe and blast it to bits. Problem solved, no one has to risk their life cutting wires. If that’s not practical, they have things like high powered water jets that they can use to blast the bomb harmlessly apart where it sits.

[BeepKillBeep]

Thanks for the reply. That’s pretty much what I thought.

Of course, I found this out the hard way by cutting random wires. You’ll be pleased to know I’m ok. One second left on the timer and everything.

[Duckster]

And then there was this bomb in 1980. It wasn’t a Hollywood bomb. It was real, and it was impossible to disarm.

[Joey_P]

While I bomb could be, by the technology of EE, designed to do just about anything (including speeding up if the ‘wrong’ wire is cut), as BeepKillBeep said, the Red Wire or the Blue Wire is essentially nonsense. Think about it, if you’re designeing a bomb, meant to kill people and there’s a wire that will disarm it (be it one to detonator or timer or battery or cell phone connection etc), are you really going to check the Anarchist’s Cookbook or the NEC to see what color that wire is ‘supposed’ to be? Nope at best you’ll use whatever wire you have handy, at worst, you’ll make it as confusing as possible. Again, as was said above, likely, the bomb would be purposely detonated on or near the site or taken away and detonated offsite to render it safe (so to speak). If they really wanted, for whatever reason, to make sure it didn’t explode, they go all Hurt Locker on it or sent in a robot to get a closer look at the wiring and decide which wire(s) to cut.

But to reiterate, if I were to make a bomb, I’d use whatever wires I had on hand (hell, they might even all be the same color) and I certainly wouldn’t follow some guide, at least not down to ‘the red wire goes from the timer to the detonator, the blue wires goes from the timer to the battery, the coiled up yellow wire makes the timer go double time if it’s cut’. I mean, even if you did follow that, you’d be silly not to switch up the color scheme.

Oh, and one last thing, if using a specific color of wire were protocol for disarming a bomb, bomb techs would know that and bomb diffusing scenes wouldn’t be 10 miutes long with dramatic music playing in background.

[RivkahChaya]

BTW, there’s a fantastic book called*Danger, UXB* about the bomb disposal squads in the UK in WWII. It was also a BBC miniseries that played on Masterpiece Theatre in the US around 1980.

I highly recommend both the book and the show, especially if you want real suspense around bomb disposal, that’s not “cut the red wire” Hollywood crap.

[si_blakely]

@Joey_P

While I bomb could be, by the technology of EE, designed to do just about anything (including speeding up if the ‘wrong’ wire is cut), as BeepKillBeep said, the Red Wire or the Blue Wire is essentially nonsense. Think about it, if you’re designeing a bomb, meant to kill people and there’s a wire that will disarm it (be it one to detonator or timer or battery or cell phone connection etc), are you really going to check the Anarchist’s Cookbook or the NEC to see what color that wire is ‘supposed’ to be? Nope at best you’ll use whatever wire you have handy, at worst, you’ll make it as confusing as possible.
…
But to reiterate, if I were to make a bomb, I’d use whatever wires I had on hand (hell, they might even all be the same color) and I certainly wouldn’t follow some guide, at least not down to ‘the red wire goes from the timer to the detonator, the blue wires goes from the timer to the battery, the coiled up yellow wire makes the timer go double time if it’s cut’. I mean, even if you did follow that, you’d be silly not to switch up the color scheme.

From the point of view of the person assembling the bomb, they want to know exactly which wire goes where, for the avoidance of mistakes when completing and arming the explosives. This is very difficult if all the wires are the same colour.

I have seen some diagrammed images of of an IRA briefcase bomb (in a newspaper, but google is failing me). This had an external arming mechanism (a magnet and reed switch, as I recall), a microswitch on the lid and a mercury tilt switch to prevent tampering. The point was that several mechanisms could allow the bomb to trigger prematurely during assembly, and getting things wrong would be lethal to the bomb-maker. So the wires were coloured. But the colours only had meaning to the specific bomb-maker.

[Bullitt]

Fallon is the champion!

Fallon is the champion

[Musicat]

@engineer_comp_geek

Cutting wires would also be a last resort for a modern bomb disposal unit.

Tell that to these guys. (NJ bomb disposal unit that triggered an explosion when they cut the wrong wire)

[watchwolf49]

@Bullitt

Fallon is the champion!

https://m.youtube.com/watch?v=4vCvm3gEEzE

What’s up with the oscilloscope there … we could adjust the trace so we could see the actual waveform … duh … and since when do luxury cruise ships pack them along … maybe I’m missing something here … I’m trying to read here in my cookbook but my Arabic is a little weak this morning.

[bob_2]

I always wonder why they don’t either cut the wire of pull the detonator out. Why mess about with the timing and trigger mechanisms when you could neutralise it, or reduce a big bang to a small one.

[si_blakely]

@bob_2

I always wonder why they don’t either cut the wire of pull the detonator out. Why mess about with the timing and trigger mechanisms when you could neutralise it, or reduce a big bang to a small one.

Because you can’t see if there is a microswitch below the detonator with another battery embedded into the explosives, or a failsafe wire hidden in the lead to the detonator that will trigger detonation.

These things are not likely, but are possible. In most situations, EOD prefer to explosively disassemble the device to prevent a much bigger detonation, and collect the pieces afterwards.

[Joey_P]

@si_blakely

From the point of view of the person assembling the bomb, they want to know exactly which wire goes where, for the avoidance of mistakes when completing and arming the explosives. This is very difficult if all the wires are the same colour.

I have seen some diagrammed images of of an IRA briefcase bomb (in a newspaper, but google is failing me). This had an external arming mechanism (a magnet and reed switch, as I recall), a microswitch on the lid and a mercury tilt switch to prevent tampering. The point was that several mechanisms could allow the bomb to trigger prematurely during assembly, and getting things wrong would be lethal to the bomb-maker. So the wires were coloured. But the colours only had meaning to the specific bomb-maker.

Seems like an occupational hazard to me.

But still, I don’t think terrorists are going to use similar color coding (like we would with regular US electrical wiring) just to make sure they don’t blow themselves up. But, as you said, it really only needs to matter to the bomb maker. One could look up how to make up a bomb on the internet and change Red to Blue and Green to Yellow and so on until they’re done. They could even make the bomb ‘properly’, then go and swap out all the wires 1:1 with random colors, even swap them out all with one color and leave the ‘make it live’ one disconnected and connect it when they’re ready.

[Joey_P]

@Musicat

Tell that to these guys. (NJ bomb disposal unit that triggered an explosion when they cut the wrong wire)

That’s an interesting idea. As long as the SOP is to blow it up anyway (but maybe not in downtown NJ), let a robot go in and hack away it wires. If it gets lucky, they can have it attempt to remove the charge. I know some information get be gotten from what’s left of the exploded bomb (as well as the shape of the fireball, sound of the explosion, color of the smoke etc), but I have to imagine so much more is there before it’s blown up.

I’m kind of curious as to why they chose to do it there instead of transporting it to a remote location. Also, they must have been really confident, those cruisers look really close. Like if this was a ‘it’s gonna blow for sure’ situation, they would have had them back off at least another 100-200 feet.

[Spiderman]

@Joey_P

That’s an interesting idea. As long as the SOP is to blow it up anyway (but maybe not in downtown NJ), let a robot go in and hack away it wires. If it gets lucky, they can have it attempt to remove the charge. I know some information get be gotten from what’s left of the exploded bomb (as well as the shape of the fireball, sound of the explosion, color of the smoke etc), but I have to imagine so much more is there before it’s blown up.

I’m kind of curious as to why they chose to do it there instead of transporting it to a remote location. Also, they must have been really confident, those cruisers look really close. Like if this was a ‘it’s gonna blow for sure’ situation, they would have had them back off at least another 100-200 feet.

I’m sure the EOD guys a) have a good idea of the size of the boom from the size of the device & b) know the formula for lethality (eg. for every add’l 10’ it’s 20% less lethal.) Also remember that fenders are a lot stronger than skin; what might injure a person might only cause a chipped paint in the cruiser.

[Joey_P]

@Spiderman

I’m sure the EOD guys a) have a good idea of the size of the boom from the size of the device & b) know the formula for lethality (eg. for every add’l 10’ it’s 20% less lethal.) Also remember that fenders are a lot stronger than skin; what might injure a person might only cause a chipped paint in the cruiser.

I agree, but, OTOH, shrapnel can fly a long way, is sharp and can be unpredictable. Sure, they know that a bomb made out of X explosives and (appearing to be) Y pounds will explode with Z force, but I doubt even the experts can predict with enough accuracy to say how far the shrapnel will fly.

Besides, it didn’t go off randomly, they were up there messing with it so they knew if and when something might happen, all they had to do was ask a few cops to move their cars further back.

[aldiboronti]

Nitpick: you don’t, as in several of the posts above, diffuse a bomb, you defuse it.

[Ludovic]

If you explode it, you do both.

[Spiderman]

@Joey_P

I agree, but, OTOH, shrapnel can fly a long way, is sharp and can be unpredictable. Sure, they know that a bomb made out of X explosives and (appearing to be) Y pounds will explode with Z force, but I doubt even the experts can predict with enough accuracy to say how far the shrapnel will fly.

Besides, it didn’t go off randomly, they were up there messing with it so they knew if and when something might happen, all they had to do was ask a few cops to move their cars further back.

I’m saying the cars may be there deliberately; far enough away to not be badly damaged but close enough to block some shrapnel.

[carnivorousplant]

@Spiderman

I’m sure the EOD guys a) have a good idea of the size of the boom from the size of the device & b) know the formula for lethality (eg. for every add’l 10’ it’s 20% less lethal.) Also remember that fenders are a lot stronger than skin; what might injure a person might only cause a chipped paint in the cruiser.

Perhaps the police car shields people from the possible explosion.