But they do refuse to observe Daylight Saving Time in the summer, because the Israeli government approved it.
On at least one occasion, that resulted in a bomb blowing up prematurely, killing the bombers who were on the way to hide it in a public place – miscommunication about which clock the timer in the bomb had been set to.
They got a Darwin Award for that, didn’t they?
One of the items on the Evil Overlord list is “I will never employ any device with a digital countdown. If I find that such a device is absolutely unavoidable, I will set it to activate when the counter reaches 117 and the hero is just putting his plan into operation.”
SIDEKICK: Are we too late?
HERO: No, don’t worry, there’s five minutes le-
boom
But the OP assumes cutting the right wire will stop the bomb. If this is the situation, and the bomb is not rigged with an ampere meter set to react to any sudden change, then why would it matter which wire was cut?
Anyone interested in this genre should check out Danger UXB. It was a British series about a WWII bomb disposal unit defusing German bombs.
Same question as before : how can you be absolutely, perfectly sure it’s not rigged to an ampere meter, or similar “don’t mess with me bomb” device ? I mean, obviously if there are no anti-tampering measures, then yes, the probable outcome of cutting a wrong wire (one that isn’t critical to the whole system) is that the bomb will, well, still be on.
However, there could be another possibility : that the wire being cut is one linking the main circuit (from power source to explosive) to whatever delaying mechanism was put in place. The rest of the circuit, cut off from it, then acts as if the delay was over, and immediately switches on.
The standard procedure for the bomb technician would then be to jump up 40 feet and scatter himself over a large area, I believe 
A basic bomb has a number of elements - a timer, a battery, a detonator, and some explosives. The simplest disarming maneuver is to disconnect the detonator from the battery/timer circuit - with no power, the detonator will not go off, even if the timer completes the count-down. The second best option is to disconnect the battery - again, the battery is needed in circuit to initiate the detonator. The final option is to stop the timer.
In the real world, there are other factors - the bomber must construct, transport and arm the bomb with regard to his own safety. This may involve an external switch or wire link that is removed to arm the bomb, and to enable the anti-tamper devices after a suitable delay. Once the bomb is armed, it must resist efforts at disarming. This is where fake detonators,microswitches, motion and light sensors are often used to prevent the bomb being moved or examined once armed. The movie trope of the bomb case being removed to expose the bomb (and the wires) is not generally credible - a real bomb would detonate at that point to prevent examination. For this reason, a controlled detonation is the preferred method - a shaped charge that disrupts the bomb and prevents detonation of the main explosive is messy but reduces the risk of injury to the bomb squad.
In the case of military bombs, unexploded ordinance denies access to an area far longer than an exploded bomb, ties up the services of highly skilled explosive disposal teams, and places them in considerable danger. While the bomb details may be known (military weapons are constructed to a known pattern by type), but the specific reason for the UXB makes the bomb exceptionally dangerous, as a small change may finally trigger the bomb. Recovering and analysing a new bomb type was a vital and risky job carried out by the UXB teams during WW2 to determine defusing methods and failure modes. This is also carried out by bomb disposal teams in Iraq/Afghanistan to counter the increasingly sophisticated IED bomb threat.
Yeah, but the detonator should have gone off with a pretty substantial pop and oozing explosive if that was the case. It happened to the July 21/7 bombers in London, and the onlookers certainly knew when the detonators went off.
Si
I am majoring in electrical engineering, and although I have no real knowledge of bomb defusing I am pretty good with electronics.
A very common timing chip is called the 555 timer. The number on it will be something like LM555 or NE555 or maybe even 556. The 555’s will have 8 pins, the 556 will have 14. Each of these could be rigged as a 1-shot with a manual override (it’s built into the chip to have a reset) and it’s by far the most common timer. Look at it with the notch facing up.
555 chips: The positive supply is top right, the ground is top left. The output of the timer is 2nd from the bottom on the left half. If the circuit is bare bones (just the timer with 2-3 capacitors/resistors) you can cut the output of the timer. Be wary of capacitors connected to power supplies or outputs to transistors (3 pin components) because these could be triggering circuits.
556: just go away because this chip contains 2 timers and they could be rigged in a very sophisticated way. If you have to, find the supply voltage on the 556 timer (top right if the notch is facing up) and, after removing any capacitors attached to it (these act like short term batteries) cut this wire. If there are extra transistors I would avoid tampering.
There could also be a resistor/capacitor circuit with a very long time constant designed to eventually turn on/off a transistor. Cut the wire closest to the bomb.
Also people usually focus on removing the supply voltage and will set up sophisticated plans around this. If there are 10 wires giving supply and only 1 wire as ground, then cutting the ground wire might be much easier.
My father was a naval bomb disposal officer in WWII. He was issued a camera and given instructions to photograph any device before he started working on it, then walk back and leave the camera on the front seat of the jeep. That way if he and his assistant were blown to smithereens there would be some record of what had killed them. :eek:
BTW, I suspect the “cut the blue wire” trope is a holdover from bomb disposal scenes in war movies. With unexploded military ordnance there typically would be a specific pattern to the color coding of the wires.
Or you could also put it in a hurt locker.
Hell, I don’t, and I’m only wiring up audio stuff. I have red wire. Everything is red. The two things that would work are covered by current remotes:
Drown it. As Smoky the Bear would say, stir the ashes and drown it again.
Blow the shit out of it with a 12ga and bird shot.
Ah, the good ol’ days of Casual Explosives. Can you imagine kiddie shows these days being interrupted with PSAs telling kids, “If it looks like this, don’t pick it up?”
ETA: The 50s and 60s were a simpler, louder, time.
I also wonder -
How likely is a bomb, say, on a bus to have tamperproofing that causes it to blow when it is disturbed? Obviously someone who has never driven on the sort of streets busses use.
Generally, uness it’s really sophisticated, won’t a bomb just be blasting caps stuck in the less explosive mix? pull them out of the gel or the fertiler and deisel mix, and the blast may take of a few finger while you cut wires, but it won’t set off the main explosive. Simple booby traps like a pressure switch under the cap that goes off if you pull on the cap? I’d really want to be sure those are pushed down before I turn the power on on the timer, if I’ve been walking or driving all over the place with that bomb.
Finally - caps need a current to go off. The simplest trick would be to short out the wires so it doesn’t.
Yeah, caps are nasty. The demo we got, they put one in a pop can, blew it up in a thick metal pipe, then fished out the fragments of aluminum. That would take out most of the fingers and possibly the palm, I’m sure.
From the wikipedia URL - “A common hazardous practice is crimping caps with one’s teeth; an accidental detonation can cause serious wounds to the mouth. Proper recommended procedure is to position the crimping tool and tighten it up, then hold it behind oneself slightly below waist level while actually crimping. While embarrassing, injuries are not serious.” :eek::eek::eek:
Serious wounds to the mouth? I’d say so. When I was getting my blaster’s ticket they showed a picture of a guy who tried to strip the wires on a detonator by biting and pulling. The front of his head really did look like it had been folded inside out. I used to arm perforating guns when I worked on the oil fields and we were provided with a thick-walled steel tube about eight inches long that received the detonator as it was wired to the firing system. If it didn’t go off when you wired it up, you could take it out of the steel tube and connect it to the detonating cord inside the perforating gun. Hold it behind my back? No thanks.
People used to ask me, “You work with explosives? Do you ever play with any of that stuff?” Well, the shock wave off a shaped charge can be two million PSI, and detonator cord ignites at six miles per second. So, “No.”
:eek: Never heard that before. Can you explain or give me a cite?
From here: (warning - pdf)
http://www.nps.gov/history/history/online_books/npsg/explosives/Chapter6.pdf
Not necessarily. If the timer circuit is homebrewed, cutting the wire from the clock pulse to the counter would indeed stop the numbers, without blanking them - in fact, there are other things you could do that would result in such a circuit speeding up in its countdown (which is another popular movie trope).
However, there’s little reason for the signal from the timer component to the counter to be going through a discrete, insulated wire that can be snipped - it would probably be a track on a PCB, or in the case of a non-homebrewed timer device, all part of the same integrated circuit
I forget where I heard this - possibly the article by Cecil that I was too lazy to look up several months ago on page one of this zombie - but I heard that this idea originated back in WWII. Germany was bombing the crap out of England with mass-produced bombs, and unexploded bombs were a real problem. Because they were mass-produced, the wire colors actually were consistent, so the idea made sense back then.
Many of the unexploded bombs, especially later on, were deliberate – the Germans had learned that an unexploded bomb was actually more disruptive than one that exploded. (Rather like an injured soldier is more costly to the enemy than a dead one, because he costs 1 or 2 other soldiers, who have to care for him.)
So they built bombs designed to not explode immediately, but with triggers to explode when moved, or with booby traps (anti-removal devices) so they would explode, killing the bomb squad when they tried to remove the trigger.
[Based on a BBC series about WWII unexploded bomb squads, and the book about it, which has pictures & diagrams of German bombs. But I don’t recall their being wires (of any color) in them – they were mostly parts like springs, triggers, blasting caps, etc.]
Looks like I have to be careful with my “humour”. I was actually trying to be facetious about what might get wounded if it blew while you were “holding it behind oneself slightly below waist level while actually crimping”. Oh well.