Preasure Cooker Bomb? WTF?
When I heard that the bombs used in the attack in Boston were “pressure cooker bombs”, I knew right away what that meant and didn’t think twice about it, at least until I talked to my sister. She had no idea what it was, specifically what good the pressure cooker did. I did something we all do from time to time, I assumed, since it was pretty basic knowledge to me, that everyone else knew, it’s an experts folly.
I don’t claim to be an expert on explosives or bomb making, but I know plenty enough to be dangerous and I’ve made explosives before, I’m going to do so tomorrow in fact but more on that in a moment. I just thought it might be useful to explain how these bombs work and the basic physics and characteristics of some common explosives. Again, I am not an expert by any means, but I can share some knowledge. Obviously I’m not going to get into the details of how one might make a bomb, there is already plenty enough of that floating around the internet.
The Boston bombs were essentially pipe bombs, just without the pipe. They used gunpowder of some kind, from fireworks if the news can be trusted. Gunpowder is a fairly simple concoction of three things: a fuel (charcoal normally, but sugar will also serve), an oxidizer (saltpeter, probably a few others would work) and a stabilizer to help make a smooth and reliable ignition. Gunpowder is a very low velocity explosive, it burns slowly, and this is where the pressure cooker comes into play.
In a gun, generally the longer the barrel the faster the bullet will go, so gunpowder is perfect, it doesn’t go up all at once, but comparatively slowly, providing constant energy to the projectile until it leaves the end of the barrel. Higher velocity explosives would drive pressures too high, so the slow burning is a great feature. Now if you simply light a pile of gun powder it goes poof, a million videos of which you can find on youtube if you are interested. The pressure cooker allows pressure to build much much higher, eventually (a fraction of a second) the cooker fails, expelling unburned powder, a shockwave, and anything else the bombmaker might have packed in there with it, ball bearings, nails, things like that, plus the cooker itself.
A pipe bomb works on the same principle.
Now there are plenty of more energetic explosives out there, so why use gunpowder? Well the explosive I’ll be making tomorrow is called “tannerite” and it is a bitch to set off. It’s perfectly legal to own and use and my use will be as a target for shooting. To make it detonate you have to use a rifle one with some “punch”, because nothing less will touch it off. ANFO is another similar explosive that has the same issue, it is very stable, and requires some kind of a booster to make it detonate.
In contrast, gunpowder will touch off with little trouble, making it a “good” choice for an application like bombing a marathon, as long as the bomb is designed to build some pressure up, a Tupperware container won’t do it.
I’ll say once again that my purpose here isn’t to give instructions for building a bomb or making explosives, just to give a little background so that you understand what exactly they are talking about on the news and what they will be talking about in what I am certain will be a trial indistinguishable from a circus.
You might wonder why explosives like gun powder and tannerite, and their constituent parts aren’t more controlled. It’s a simple answer, you just can’t. Tannerite is a mixture of ammonium nitrate and aluminum powder, and I’ve already said what gunpowder is made of, ANFO is the same as tannerite, just with fuel oil instead of metal powder. Fertilizer and heating oil, powdered metal, sugar/charcoal, potassium nitrite and sulfer, all impossible to regulate or restrict. Unlike with guns, there is such a small amount of difficulty involved that there is simply no way to control any of it, except perhaps limiting single purchase quantities.
Hopefully that all will teach you something and fill in what has been a sort of missing puzzle piece for those unfamiliar with IED’s and explosives.