Interview with an expert in improvised explosive devices

At Scientific American, Larry Greenemeier has a piece about the science behind the three (possibly four) improvised explosive devices that killed at least three people yesterday in Boston. It might be easy to build bombs like these, but their DIY construction techniques also leave clues that help investigators find the people responsible.


  1. I find it interesting that, even though reports that the cell network was taken down seem most likely false, the network did indeed go down because of the heavy volume of calls (I was in Cambridge).

    It seems that if the IEDs were set to be triggered by cell phones, the very nature of the panic calling might itself have prevented the remaining devices from being triggered. Almost like a self-protective mechanism.

    1. That’s a very interesting aspect of this. It seems like the number of deaths (not necessarily injuries, severity or number) and the raw amount of panic were mitigated or minimized by the sheer volume of first responders and first aid/medical infrastructure on site. Like wise the huge police presence and sheer volume of press, spectators, and cameras in and around the marathon might make locating the culprit at least somewhat easier. And, it seems, had an effect on locating and disabling additional devices. Its almost like attacks on events of this sort are self limiting in some ways.

  2. Some thoughts on design:
    Why ball bearings for shrapnel?
    I suppose they could have been BBs which is likely more readily available than actual ball bearings.
     But why not just nails, screws, etc. I would think that those would cause much more damage than something smooth and round. Perhaps you can pack more pieces in?
    If I remember anything from the Anarchist Cookbook I read forever ago (or maybe it was a Tom Clancy book :) it described a bomb specifically using ball bearings. Just saying it’s a very interesting choice.
    Another is how well directed the blast was, low to the ground and I didn’t see practically any blast upwards. Definitely a more sophisticated design than crudely throwing it together. I remember how the Oklahoma City bomb was very carefully designed to focus the blast toward the building.  Similar thought would have had to be put in here.
    Third was the white smoke and lack of smell. Rules out a lot of gunpowder based bombs, likely dynamite. The actual blast itself was ‘slow’ at least compared to C4 (thanks Mythbusters) or some military or demolition explosive. Also AmFo, fertilizer based explosive, would need a huge amount of it to make a big enough explosion, like a garbage can full of the stuff.
    Here’s a thought about cell phone detonation, wouldn’t you want to test the firing mechanism before you hooked it up? Once the feds get the cell records, can’t they trace the # to that test call and find out exactly where it was built?

    1. Also AmFo, fertilizer based explosive, would need a huge amount of it to make a big enough explosion, like a garbage can full of the stuff.

      Not to mention those require a starter explosive.

      I’m curious about that pressure cooker….was it simply an off the self part?  I mean those would hold together somewhat well, but frankly some black iron pipe from the hardware store would probably withstand a higher initial pressure build up.  Now something more industrial, like a pressure vessel/reactor…then yeah those could withstand a great deal of stress before coming apart.

      1. Online articles are now saying that pressure cookers are a thing in IED manufacturing circles so this bomb builder seems to have been using a design from somewhere.

        Maybe the FBI is getting a list of pressure cooker purchases in the last couple of months (who needs two of them?) and paying the new owners a visit to check out their kitchens.

        edit: I guess pressure cooker purchases by men will be another thing they will look for.

    2. Ball bearings are actually a really common choice for shrapnel, both in improvised devices and manufactured ones. That’s because its quite effective,and easy to come by. I don’t think BB’s would do much damage , but larger balls would be pretty devastating. Think of the difference between bird shot (often BBs) and buck shot in a shotgun cartridge. Modern hand grenades and the famous claymore mine both use larger sizes of ball bearing for anti-personnel purposes. They’ve got more weight and better ballistics than screws/nails and scrap. But I’ve also seen reference to the general junk and ball bearings being used together in these devices. 

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