Blowing a vault.

     Ann Charles sent me a great one this morning. A writer she knows was complaining in her blog that she couldn’t find information about what explosives to use to blast open a bank vault. She sent me the link and asked me if  could have helped. This is what I said:

     “Yep.

     First you have to start with the basic principle of how explosives work (super fast fire) and then decide that kidnapping the bank manager is a much better way of going. No super hot jets of molten steel and explosives roasting the inside of the vault.

      Just kidding. Basically, you’d use shaped charges (the explosion is directed in a specific direction) over the lock and where you figured the locking cylinders were located. That is how I would have described it, blocks of something taped over the lock and spaced evenly around the door with wires going to a timer. So, sort of how she did, but what she described was more of what you would use for anti-personnel, the pipe gets shredded by the explosion and it and anything in it are used to do damage to soft targets. Really, what she needed wasn’t the type of explosives used (C-4, Octol, Semtex) but the correct method of how the force was applied.”

     Granted that’s an overly simplistic explanation but Ann did ask before I’d had breakfast or more than a few sips of my mocha.

     The writer in question was looking at it from the angle of what type of explosives to use, not how the explosion is used to do work. Everyone has seen a bank vault door, if not in person, in a movie or on tv. They are big, heavy and thick. I used to be a bank manager and I can tell you blasting a vault door without leveling the bank at the same time would be something best left to an expert.

     In the case of a vault door, the explosive force is used to cut metal, and in a fairly precise manner so that the amount of explosives can be kept to a minimum. From the bank robber’s point of view, not being heard is a good thing, not blowing all the windows out of the front of the bank is an even better thing. The character in the story in question was not an expert on explosives so the description doesn’t have to be accurate on a scientific level, only a general level. The reader needs to believe the description the character is giving too, even if they are an expert. That’s the tricky (and fun) bit.

     In my description of what I would from above, based on my first hand knowledge of vault doors, this is roughly how I would sketch out the details:

• spaced around the perimeter of the door where it meets the frame, a series of  lumpy, blocky looking masses about the size of a large bar of soap held in place be lots of strips of duct tape (no need for something fancy here, duct tape is cheap and readily available).
• A few more (3 or 4 maybe) around the dial mechanism and handle
• wires running from all of these to a timer/detonator of some kind. It could be a digital timer or a dial type kitchen timer or wires to the speaker of a cell ph0ne so it blows when the phone rings (you’d probably want to keep that number private…)

     That level of detail covers all the elements you’d need for blasting without too many details that might not be right, which is what tends to annoy experts (and knowledgable amateurs). In my opinion this is the part of story telling that is best left to the reader’s imagination. An expert in explosives & blasting is going to say, “hey, they must have x grams for each charge…” and the reader that knows nothing about the topic is going to be wondering what is next: will the vault door get blown open or will it be defused in time.