Perry Metzger is a chemistry student at college. Last week he wrote a rather insightful message to a friend of his regarding the “liquid terrorist” threat, and it’s been spread around the internet. It’s rather long, so I’ll quote parts of it here.

Based on the claims in the media, it sounds like the idea was to mix H2O2 (hydrogen peroxide, but not the low test kind you get at the pharmacy), H2SO4 (sulfuric acid, of necessity very concentrated for it to work at all), and acetone (known to people worldwide as nail polish remover), to make acetone peroxides. You first have to mix the H2O2 and H2SO4 to get a powerful oxidizer, and then you use it on acetone to get the peroxides, which are indeed explosive.

A mix of H2O2 and H2SO4, commonly called “piranha bath”, is used in orgo labs around the world for cleaning the last traces out of organic material out of glassware when you need it really clean– thus, many people who work around organic labs are familiar with it. When you mix it, it heats like mad, which is a common thing when you mix concentrated sulfuric acid with anything. It is very easy to end up with a spattering mess. You don’t want to be around the stuff in general.

Now you may protest “but terrorists who are willing to commit suicide aren’t going to be deterred by being injured while mixing their precursor chemicals!”– but of course, determination isn’t the issue here; getting the thing done well enough to make the plane go boom is the issue. There is also the small matter of explaining to the guy next to you what you’re doing, or doing it in a tiny airplane bathroom while the plane jitters about.

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. In short, it sounds, well, not like a very good idea.

The news this morning was full of stuff about “ordinary looking devices being used as detonators”. Well, if you’re using nasty unstable peroxides as your explosive material, you don’t really need any– the stuff goes off if you give it a dirty look. I suspect a good hard rap with a hard heavy object would be more than sufficient. No need to worry about those cell phones secretly being high tech “detonators” if you’re going this route.

There are other open questions I have here as well. Assuming this is really what was planned, why are the airport security making people throw away their shampoo? If you open a shampoo bottle and give it a sniff, I assure you that you’ll notice concentrated sulfuric acid very fast, not that you would want to have your nose near it for long. No high tech means needed for detection there. Acetone is also pretty distinctive– the average airport security person will recognize the smell of nail polish remover if told that is what they’re sniffing for.

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.

See the elderly gentleman with the cane? Perhaps it is not really an ordinary cane. The metal parts could be filled with (possibly sintered) aluminum and iron oxide. Thermite! Worse still, nothing in a detector will notice thermite, and trying to make a detector to find thermite is impractical. Maybe it is in the hollowed portions of your luggage handles! Maybe it is cleverly mixed into the metal in someone’s wheelchair! Who knows?

Also, we can never allow people to bring on laptop computers. It is far too easy to fill the interstices of the things with explosives– there is a lot of space inside them– or to rig the lithium ion batteries to start a very hot fire (that’s pretty trivial).

Then, lets consider books and magazines. Sure, they look innocent, but are they? For 150 years, chemists have known that if you take something with high cellulose content– cotton, or paper, or lots of other things– and you nitrate it (usually with a mixture of nitric and sulfuric acids), you get nitrocellulose, which looks vaguely like the original material you nitrated but which goes BOOM nicely. So, naturally, we have to get rid of books and magazines on board. That’s probably for the best, as people who read are dangerous.

Now, books aren’t the only things you could nitrate. Pants and shirts? Sure. It might take a lot of effort to get things just so or they will look wrong to the eye, but I bet you can do it. Clearly, we can’t allow people on planes wearing clothes. Nudity in the air will doubtless be welcomed by many as an icebreaker, having been deprived of their computers and all reading material for entertainment.

It isn’t entirely clear that even body cavity searches would be enough. If we’re looking for a movie plot, why not just get a sympathetic surgeon to implant explosives into your abdomen! A small device that looks just like a pace maker could be the detonator, and with modern methods, you could do something like setting it off by rapping “shave and a haircut” on your own chest. You could really do this– and I’d like to see them catch that one.

So can someone tell me where the madness is going to end? My back of the envelope says about as many people die in the US every month in highway accidents than have died in all our domestic terrorist incidents in the last fifty years. At some point, we’re going to have to accept that there is a difference between real security and “security theater”, and a difference between realistic threats and uninteresting threats. I’m happy that the police caught these folks even if their plot seems very sketchy, but could we please have some sense of proportion?