Perry Metzger wrote a fascinating post on Interesting-People about the difficulty of using liquid explosives — and pointing out that you’d also have to forbid many other substances to get that job done.
So, lets say you have your oxidizer mixture and now you are going to mix it with acetone. In a proper lab environment, that’s not going to be *too* awful — your risk of dying horribly is significant but you could probably keep the whole thing reasonably under control — you can use dry ice to cool a bath to -78C, say, and do the reaction really slowly by adding the last reactant dropwise with an addition funnel. If you’re mixing the stuff up in someone’s bathtub, like the guys who bombed the London subways a year ago did, you can take some reasonable precautions to make sure that your reaction doesn’t go wildly out of control, like using a lot of normal ice and being very, very, very careful and slow.
On an airplane? On an airplane, the whole thing is ridiculous. You have nothing to cool the mixture with. You have nothing to control your mixing with. You can’t take a day doing the work, either. You are probably locked in the tiny, shaking bathroom with very limited ventilation, and that isn’t going to bode well for you living long enough to get your explosives manufactured.
We’re stopping people from bringing on board wet things. What about dry things? Is baby powder safe? Well, perhaps it is if you check carefully that it is, in fact, baby powder. What if, though, it is mostly a container of potassium cyanide and a molar equivalent of a dry carboxylic acid? Just add water in the first class bathroom, and LOTS of hydrogen cyanide gas will evolve. If you’re particularly crazy, you could do things like impregnating material in your luggage with the needed components. Clearly, we can’t let anyone carry on containers of talc, and we have to keep them away from all aqueous liquids.
My understanding, which is as sketchy as Metzger’s but without the science background, is that the would-be London terrorists had rigged shampoo bottles and the like to have multiple compartments inside. Chemicals which are not dangerous on their own would be stored in the compartments and then mixed all at once by collapsing the compartments. What he’s written here doesn’t seem to invalidate that theory, although I certainly can’t claim to verify it with my limited knowledge. I should also point out that you don’t need a major explosion to bring down a plane – simply starting a hard-to-control fire seems like it might be enough.
As for the rest of the post, he unfortunately reverts back to the trifecta of twisted logic that has clouded this debate since 9/11/01:
1) It’s so easy to get a bomb on a plane that we shouldn’t bother checking.
2) Bombs on planes are so rare (rarer than death by heart disease, traffic accidents, you name it), that we shouldn’t bother checking.
3) Our methods of checking are so ineffective that we shouldn’t bother checking.
First of all, #1 and #2 both sound true, but are diametric logical opposites, proving that one can make any statement sound true if he/she really wants to. Second, there’s the implicit (and false) assumption that we shouldn’t protect ourselves from things that happen infrequently. If that were true, there wouldn’t be traffic lights at rural intersections, homes wouldn’t have burglar alarms, and restaurants wouldn’t have first aid kits. I mean seriously – you’re more likely to die in your bathtub, right?
As for #3, most airport security measures are not implemented to stop every bomb or catch every terrorist. They’re implemented as a show of force – an attempt to tip the risk/reward calculation in the terrorists’ minds away from attacking airports, and a way to make the passengers feel safer before getting on the plane. And if you think passenger comfort isn’t part of what the airlines are selling…
What bugs me about the latest round of restrictions is the explicit list of exceptions we published along with the rules. If you’re going to announce that all liquids are banned except if they’re in a baby bottle or a prescription bottle, then you’re actually lowering the risk for a terrorist. All one has to do is put their little concoction in one of those two containers, and they’re almost guaranteed access to the plane.