When defusing a bomb, why can’t you just cut all wires at once?
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In theory, it’s possible that an attacker could have foreseen such an attempt, as design a weapon that responded to the loss of conductivity/power on a circuit as a trigger for detonation.
That’s essentially what bomb disposal robots do. They put a small explosive up against the bomb and detonate it to physically move all the bomb parts away from each other, breaking all the wires at once.
But, if you’re a clever evildoer, bombs can be made with mechanical protection for their detonators – like putting them inside the pipe with the explosive. The wires charge up a capacitor and when the electrical input goes away the bomb detonates. If you cut wires in such a bomb, you set it off while you’re right next to it, not good.
Because “cut the blue wire” is a movie/TV trope and not based on reality. There are many, many way to build a bomb’s detonation device. “Cut the wire” was just something that would build tension on screen
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Most bombs are simple and cutting the power or detonator wires would disarm it. But it’s trivial to design bombs with failsafes so that if it were tampered with, it would explode. Of course, there is no standardization of such design, and certainly no standard colors (i.e. “cut the green wire” is ridiculous)
There have been bombs specifically designed to fool the disposal people with the actual trigger mechanism obscured. Cutting the “obvious” wire being what causes the detonation.
Sometimes X-ray machines are used to examine the bomb, but in reality, if it’s not clear how to defuse it, they will just evacuate and blow the bomb up “in place”.
If you’re 5:
Because then the bad guys would reverse the bomb’s computers to blow up the bomb not when current is flowing through them, but when the current flow ends. Go ask your teacher (Google) about “Normally closed” and “Normally Open” button logic.
If you’re older:
Because not many bombs necessarily actually have wires to cut. C4 blasting caps do certainly. TNT technically only needs a source of flame, so there could be a sparker attached directly to the exposed dynamite. Same with gasoline or ampho. A bunch of grenades don’t need wires, and can be mechanically booby trapped inside a box or room. And of course, in computer time, it’s impossible to cut all wires at once. The bomb could detect you cutting the power supply first and be programmed to instantly trigger the bomb as it’s losing power, or in the event of control loss, a “Normally closed” relay could trigger the bomb via a backup power source that it switches to when power is lost.
It’s safer to cut the correct wire first, as in, cut the wire to the blasting cap, or cut the wick, or whatever the trigger mechanism is.
Or even better is to just verify the type of explosive and then get a bomb disposal robot to dump a bucket of water on it. Or just evacuate and let the bomb blow up anyway. Depends on the type of explosive and the situation.
Follow up question; when a bomb has a primer (like a blasting cap or something) in the main explosives, why not just remove the primer instead of cutting wires? (Like when there’s blocks of c4 with that primer thing in there…)
Assuming there was a bomb which actually worked that way, what tool would you use to ensure that multiple wires were completely cut simultaneously, stopping the flow of electricity in all wires at the same instant? Keep in mind that electricity can travel 3 cm in 1 billionth of a second, and it does not even need to be flowing directly through a wire, thanks to induction. There’s no mechanical way to do it with the level of precision needed.
Because the bomber can have it wired so that current flowing through some of the wires is *preventing* it from exploding, and cutting any of those wires would set it off.
We have an emergency button at work. If it’s pressed it calls the police and sends out a silent lockdown alert to everyone’s E-mail.
You can’t cut the wire to the button without setting off the alert. It has a small current going through it and a resistance that is measured. If the resistance goes up or down the alert is sent out and the police are called.
We discovered this when we moved the desk that the button is attached to and unplugged it. Oops.
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